Chapter 15 - Low-Acid and Acidified Low-Acid Foods in Hermetically Sealed Containers (Canned Foods)

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Table of Contents

Introduction

This chapter is intended as a reference source for operators and inspectors concerned with heat processing low-acid and acidified low-acid foods packed in hermetically sealed containers. It is not intended to stand alone, but rather to be used in conjunction with relevant legislation, textbooks and other appropriate source materials to provide an extensive information base to assist operators and inspection personnel in the performance of their duties. It is the responsibility of the operator to be familiar with all pertinent regulations, and to understand how they apply to their products, processing operations and equipment.

15.1 Scope

This chapter is concerned with the critical control points and hygienic factors involved in the thermal processing and packaging of low-acid and acidified low-acid foods in hermetically sealed containers.

15.2 Definitions

For the purpose of this code:

15.2.1 Acidified low-acid food

means a low-acid food which has been treated in a manner so that all components have attained an equilibrium pH of 4.6 or below by the time thermal processing and cooling is completed.

15.2.2 Aseptic processing and packaging

means the filling of a commercially sterile product into commercially sterile containers followed by hermetic sealing in a commercially sterile atmosphere.

15.2.3 Bleeder

means a small orifice through which steam and other gases are permitted to escape from a retort throughout the entire thermal process and may also serve as a means of removing condensate.

15.2.4 Canned food

means commercially sterile low-acid or acidified low-acid food packed in hermetically sealed containers.

15.2.5 Cleaning

means the removal of food residues, dirt, grease or other objectionable material.

15.2.6 Code lot

means all products have an identical code. Code lots should be restricted to the same product type (formulation), container type and size and processed in the same establishment during a period not to exceed 24 hours.

15.2.7 Come-up-time

means the time, including venting time, which elapses between the introduction of the heating medium into the closed retort and the time when the temperature in the retort reaches the required sterilization temperature.

15.2.8 Commercially sterile

15.2.8.1 Food means the condition obtained in a food which has been processed by the application of heat, alone or in combination with other treatments, to render the food free from viable forms of microorganisms, including spores, capable of growing in the food at temperatures at which the food is designed normally to be held during distribution and storage.

15.2.8.2 Equipment and containers used in aseptic processing means the condition obtained by the application of heat or other appropriate treatments which render the product contact surfaces of such equipment and containers free from viable forms of microorganisms capable of growing in a food, at temperatures at which the food is designed normally to be held during distribution and storage.

15.2.8.3 Atmosphere means the condition obtained by the application of heat, or other appropriate treatments, which render the atmosphere free from viable forms of microorganisms capable of growing in a low-acid food packed in hermetically sealed containers at temperatures at which the food is designed normally to be held during distribution and storage.

15.2.9 Critical factor

means any characteristic, property, condition, aspect or other parameter, variation of which may affect the attainment of commercial sterility.

15.2.10 Disinfection

means the reduction, of the number of microorganisms (to a level that will not lead to harmful contamination of food) by means of chemical agents and/or physical methods without adversely affecting the food.

15.2.11 Equilibrium pH

means the condition attained in an acidified low-acid food product in which there is no further change in the pH of any of the components.

15.2.12 Flame sterilizer

means an apparatus in which food in hermetically sealed containers is agitated at atmospheric pressure, by either continuous, discontinuous or reciprocating movement over gas flames to achieve commercial sterility of the food. (A holding period may follow the initial heating period.)

15.2.13 Heating curve

means a graphical representation of the temperature change in the food with time throughout the thermal process. (This is usually plotted on semi-log graph paper so that the temperature on an inverted log scale is plotted against time on a linear scale.)

15.2.13.1 Broken heating curve means a heating curve which shows a distinct change in the rate of heat transfer such that the curve may be represented by two or more distinct straight lines after the retort has attained the sterilization temperature when plotted on semi-log paper.

15.2.13.2 Simple heating curve means a heating curve which approximates a straight line after the retort has attained the sterilization temperature when plotted on semi-log paper.

15.2.14 Head space

means the volume in a container not occupied by the food.

15.2.14.1 Gross head space is the vertical distance between the level of the product (generally the liquid surface) in an upright and rigid container and the top edge of the container (the top of the double seam of a can or the top edge of a glass jar).

15.2.14.2 Net head space of a container is the vertical distance between the level of the product (generally the liquid surface) in an upright rigid container and the inside surface of the lid.

15.2.15 Hermetically sealed container

means a container, designed and intended to be secure against the entry of microorganisms including spores.

15.2.15.1 Rigid container means that the shape or contours of a filled and sealed container are neither affected by the enclosed product nor deformed by an external mechanical pressure of up to 70 kPa (10 psi, i.e., normal firm finger pressure.)

15.2.15.2 Semi-rigid container means that the shape or contours of a filled, sealed container is not affected by the enclosed product under normal atmospheric temperature and pressure but can be deformed by an external mechanical pressure of less than 70 kPa (10 psi, i.e., normal firm finger pressure.)

15.2.15.3 Flexible container means that the shape or contours of a filled, sealed container are affected by the enclosed product.

15.2.16 Holding time:

see sterilization time.

15.2.17 Incubation tests

means tests in which thermally processed product is kept at a specific temperature for a specified period of time in order to determine if outgrowth of microorganisms or other problems occur under these conditions.

15.2.18 Initial temperature

means the product temperature of the coldest container to be processed at the time the sterilization cycle begins.

15.2.19 Low-acid food

means a food, other than an alcoholic beverage, where any component of that food has a pH greater than 4.6 and a water activity (aw) above 0.85.

15.2.20 Potable water

means water fit for human consumption.

15.2.21 Retort

means a pressure vessel designed for thermal processing of food, packed in hermetically sealed containers, by an appropriate heating medium and where necessary with super-imposed pressure.

15.2.22 Scheduled process

means the thermal process alone or in combination with critical factors chosen by the processor for a given product formulation, container type and size and thermal processing system to achieve at least commercial sterility of the product.

15.2.23 Seals

means those parts of a container or container material that are joined or fused to form a hermetic closure.

15.2.24 Sterilization temperature

means the temperature maintained throughout the thermal process which is at least equal to that specified in the scheduled process.

15.2.25 Sterilization time

means the time between the moment sterilization temperature is achieved and the moment cooling is started.

15.2.26 Thermal process

means the thermal treatment required to achieve commercial sterility and is quantified in terms of time and temperature.

15.2.27 Vents

means openings in the retort shell controlled by a gate, plug cock, or other adequate valves and are used for the elimination of air from the retort during the venting period.

15.2.28 Venting

means the thorough removal of air from steam retorts through the vents by introduction of steam or other appropriate methods prior to attainment of the sterilization temperature.

15.2.29 Water activity (aw)

means the ratio of the water vapour pressure of a food to the vapour pressure of pure water at the same temperature and pressure.

15.3 Background

In order to understand why certain procedures have been developed for the canning of foodstuffs, it is necessary to have some knowledge of the spoilage organisms themselves, in particular bacteria, yeasts and moulds. These organisms, by nature of their small size, are referred to as microorganisms.

Microorganisms are ubiquitous, occurring wherever conditions are favourable to them. It must not be assumed that all microorganisms are harmful. In fact the vast majority do not fall into this category and most are essential or actively beneficial to life in general. Those microorganisms which are capable of causing disease are referred to as pathogens.

15.3.1 Important General Characteristics of Microorganisms

Many microorganisms are capable of extremely rapid multiplication under favourable conditions. For example, some species of bacteria can pass through a generation within 20 minutes under optimal conditions. Since each generation potentially doubles the number of bacteria, it can be seen that enormous numbers of bacteria can be attained within a period of a few hours.

When conditions for growth or survival become unfavourable, many microorganisms have the ability to develop resistant structures known as spores, which can, if necessary, remain dormant for prolonged periods of time (several years in some instances) until conditions become favourable to support the growth of the species. At this time, the spore reverts to the growth or vegetative form.

Certain microorganisms in the vegetative form have the ability to produce toxins and these toxins may be extremely harmful to man. If such microorganisms are present in large numbers in foodstuffs, not only the microorganisms themselves, but also the toxins produced by them, make the foodstuffs unsafe for human consumption.

15.3.2 Environmental Characteristics Affecting Growth

15.3.2.1 Nutritional Requirements

Unless the microorganisms possess chlorophyll and can therefore synthesize their food requirements from water and carbon dioxide, they are dependent on an external source of food such as carbohydrates, fats and oils. In addition, they have specific requirements for minerals and vitamins. Because of the wide range of requirements by different microorganisms, any foodstuff is capable of supporting growth of one kind or another.

15.3.2.2 Moisture Requirements

Microorganisms, particularly bacteria, require water for growth. The water which is present in cells of plants or animals and hence, in a foodstuff, is largely bound within the cells and as such, is not available to microorganisms. However, free or available water is in and around tissues in a foodstuff, and it is this water on which the growth of microorganisms depends. The amount of free or available water in a foodstuff is often expressed in terms of the water activity (aw) value. If methods are employed to reduce the aw of a foodstuff, it will render it less suitable for bacterial growth. It should be noted that freezing is an effective method for preserving foodstuffs, because the tissue water is converted into ice and as such, is no longer available to microorganisms.

15.3.2.3 Environmental pH

Most foods are acidic, but to different degrees. The pH value is used to represent the degree of acidity or alkalinity of a substance. The pH scale runs from 0 to 14, with 7 being the neutral point, and any value below 7 is acid.

In general, bacteria are less tolerant than yeasts or moulds, and not only is their growth affected by the pH, but also their rates of survival during storage, heating, drying and other forms of processing.

15.3.2.4 Temperature Requirements

Each microorganism has an optimum temperature range for growth and on the basis of the temperature requirements, are classified into four groups:

Psychrophilic 14-20°C
Mesophyllic 30-37°C
Facultative thermophilic 38-46°C
Obligatory thermophilic 50-66°C

15.3.2.5 Oxygen Requirements

All microorganisms require oxygen to carry on their metabolic process. Free oxygen exists in the air, and those microorganisms which can grow in the presence of this free oxygen are described as aerobes.

However, some microorganisms exist in the absence of atmospheric oxygen and are described as anaerobes.

Most bacteria fall into a category known as facultative anaerobes, which can tolerate to some degree either the presence or absence of atmospheric oxygen. In sealed containers, anaerobic conditions exist and bacterial decomposition of the foodstuff tends to be of a putrefactive nature, sometimes leading to the formation of foul gases.

15.3.3 Clostridium botulinum

Of all the microorganisms concerned with the spoilage of food, there is one species of bacteria with which we are concerned above all others. This is Clostridium botulinum, an anaerobe, spore former and toxin producer. This bacterium produces a toxin which is the strongest biological toxin affecting man and animals. It has been calculated that 1 gram of toxin, properly diluted, could kill more than 500 million people. The food poisoning syndrome associated with the bacterium is known as botulism.

15.3.4 Low Acid Foods

Low acid foods are defined as those having a pH of 4.6 or more. Included in this category are meat products and vegetable products. The reason for selecting this value is that Clostridium botulinum will not grow at a pH of 4.8 or less. (A safety factor of 0.2 is allowed). This bacterium also requires an aw of 0.93 or greater for growth. In this instance a safety factor of 0.08 is allowed, giving a critical aw of 0.85. The definition of a low acid food is often modified to include this factor and reads "a food, other than alcoholic beverage, where any component of that food has a pH value greater than 4.6 and a water activity (aw) greater than 0.85".

A low acid food, when canned, must be subject to a thermal process incorporating a sufficiently high temperature maintained for a long enough time to ensure the destruction of Clostridium botulinum and its toxins.

15.4 Establishment: Hygienic Processing Requirements

15.4.1 Raw Material Requirements

One of the factors which influences the effectiveness of a thermal process in destroying microorganisms is the number of bacteria present in the product before heat treatment commences. It is therefore extremely important that good sanitary practices prevail during product preparation to minimize bacterial loads. The attitude that contamination, poor sanitation, etc., do not matter, as the product is going to be heat treated eventually, must be strongly resisted.

Incoming raw materials, ingredients, and packaging materials should be inspected upon receipt to ensure that they are suitable for processing. Materials must be received in an area separate from the processing areas. Prior to being placed in inventory, ingredients susceptible to microbiological contamination either should be examined for microbiological quality or should be received under a supplier's guarantee that they are of a microbiological quality suitable for use in processing low acid foods. Products must be held prior to processing in such a manner as to prevent significant growth of microorganisms.

Blanching by heat, when required in the preparation of food for canning, should be effected by heating the food to the required temperature, holding it at this temperature for the required time, and then either rapidly cooling the food or passing it to subsequent processing without delay. Thermophilic growth and contamination in blanchers should be minimized by good equipment design, the use of adequate operating temperatures and routine cleaning and disinfection. Where the blanched food product is washed prior to filling, potable water shall be used.

All steps in the production process, which includes acidification when required or used, filling, closing, thermal processing and cooling, should be performed as rapidly and as soon as possible and under conditions which will prevent contamination and growth of microorganisms of public health significance in the food.

15.4.2 Prevention of Cross-Contamination

Effective measures should be taken to prevent contamination of food material by direct or indirect contact with material at an earlier stage of the process.

Persons handling raw materials or semi-processed products capable of contaminating the end product should not come into direct contact with any end product unless and until they discard all protective clothing worn by them during the handling of raw materials or semi-processed products and they have changed into clean protective clothing.

If there is a likelihood of contamination, hands should be washed thoroughly between handling products at different stages of processing.

All equipment which has been in contact with raw material or contaminated material should be thoroughly cleaned and disinfected prior to being used for contact with end products.

15.4.3 Filling and Sealing Operations

15.4.3.1 Empty Product Containers

The material should be appropriate for the product to be packed and for the expected conditions of storage and should not transmit to the product objectionable substances beyond the limits contained in the Food and Drugs Act and Regulations. The packaging material should be sound and should provide appropriate protection from contamination. The product containers should be sufficiently durable to withstand the mechanical, chemical and thermal stresses encountered during thermal processing and normal distribution. (An overwrap may be necessary for flexible and semi-rigid containers). With laminates particular attention should be paid to ensure that the combination of processing requirements and product characteristics does not cause delamination as this may result in loss of integrity. The sealant material chosen must be compatible with the product as well as the container and closure systems. The closures for glass containers are particularly susceptible to mechanical damage which may result in a temporary or permanent loss of hermetic seal. The closures of sealed jars should be contained within the diameter of the glass body to avoid closure to closure contact of the sealed jars.

All packaging material should be stored in a clean and sanitary manner.

15.4.3.2 Examination of Empty Product Containers

When containers are received from the manufacturer or the container manufacturing section of the company, they should have already received extensive checks. However, it is important that they be reinspected by plant quality control personnel before use, for signs of damage incurred during transportation and storage and for compliance with the manufacturer's specifications. Empty containers are particularly subject to damage by faulty operation of depalletizers and by badly designed or poorly controlled conveyors to filling and seaming machines.

Immediately prior to filling, rigid containers should be cleaned in an inverted position by suitable air or water jet appliances.

Glass containers may also be cleaned by suction (vacuum). Containers intended for use on aseptic filling lines should not be cleaned with water unless they are thoroughly dried prior to sterilization. Examination is particularly important in the case of glass containers which may contain fragments of glass or glass defects which are difficult to see.

Dirty containers shall not be filled. Faulty rigid containers, e.g., those that have been dented or pierced, having defective seams, with deformed flanges, with abnormal levels of scratches or flaws in the plating or enamel (lacquer) and covers with defective sealing compound or gaskets, etc. shall not be used. Care should be taken to avoid damage to empty containers, closures and container materials which can result from faulty handling prior to closure.

The processor should ensure that the container and closure specifications are such that the container is capable of withstanding the processing and subsequent handling strains to which the containers are normally subjected. Since such specifications may vary depending upon the canning operation and subsequent handling, they should be established in consultation with the container or closure manufacturer.

15.4.3.3 Proper Use of Product Containers

Product containers must never be used within the cannery for any purpose other than packing food. They must never be used as ash trays, waste containers, receptacles for small machine parts or any other similar purposes. Such practices must be avoided because there is a considerable risk that such containers may accidentally find their way back onto the production line and result in the packing of food in the same container with very objectionable or possible dangerous material.

15.4.3.4 Protection of Empty Product Containers During Plant Cleaning

Empty containers should be removed from the packing room and from the conveyors which lead to the filling machines before production lines are washed down. If this is not practicable, they must be shielded or located so that they will not become contaminated or obstruct the clean-up operations.

15.4.3.5 Filling of Product Containers

The filling of containers is of prime importance. Overfilling or careless filling procedures may result in product being forced out of the container during closure and becoming trapped in the seams or seals, possibly leading to leakers, or in product contaminating the seal area of flexible pouches, thus endangering the closure.

The filling of containers also has a direct bearing on the resulting head space. Insufficient head space will not allow for sufficient expansion during the thermal process and in the case of glass containers, this may lead to deformation of the closure. In the case of double seamed containers, excessive pressure may result in distortion of the ends of the container.

Controlled filling, whether by mechanical or manual means, is also important in respect to heat penetration. In agitating retorts, it is the movement of the head space bubble through the product which ensures the mixing of the contents and even heat distribution throughout the product. In the case of flexible pouches, variations in filling may lead to variations in the filled pouch thickness which will affect heat penetration rates. In systems employing conduction heating, too large a head space (the air acting as an insulator) retards the rate of heat transfer.

15.4.3.6 Vacuum Production

  1. Thermal exhaust or hot fillings

    This entails heating the contents of the container at least 71-82°C prior to sealing. The contraction of the contents after closing produces the vacuum.

  2. Mechanical vacuum

    In this case the seaming chucks operate in a vacuumized environment, thereby creating the same vacuum in the sealed container. It should be noted that the temperature and the head space volume have little effect on the vacuum produced by this method.

  3. Steam displacement

    This is a process in which steam is injected into the head space, displacing the air, followed by immediate closure. The vacuum is caused by steam condensing.

    The exhausting of containers for the removal of air shall be controlled as to meet the conditions for which the process was designed.

    An increase in the amount of oxygen in the head space can accelerate the corrosion of the container, leading to detinning or even pinholing of the container. Insufficient vacuum may also lead to discoloration of the contents from oxidation.

    Too high a vacuum may lead to panelling (distortion inwards) of the container, whereas too low a vacuum can cause bulging of the containers (distortion outwards) if the outside atmospheric pressure is lowered, as is the case at higher altitudes.

    An adequate vacuum combined with a head space provides a reservoir for any hydrogen gas which might be produced during a reaction between the contents and the container. In large flat containers the vacuum serves to hold the product against the sides of the container, promoting heat transfer.

15.4.3.7 Closing Operations

Particular attention should be given to the operation, maintenance, routine checking and adjustment of closing equipment. Sealing and closing machines shall be fitted and adjusted for each type of container and cover used. Seams and other closures shall be tight and secure and meet all application. The equipment manufacturer's or supplier's instructions and specification should be followed meticulously.

Critical factors such as sealing vacuum, head space, etc., should be measured and recorded at intervals of sufficient frequency to ensure compliance with that specified in the scheduled process.

15.4.3.8 Inspection of Closures

The hermetic sealing of cans depends on the formation of what is termed a double seam, formed by the mechanically interlocking and ironing the curl of the can end and the flange of the can body. To form a hermetic seal, any voids that exist in the mechanical seal must be filled with some form of gasket material. A double seam is formed in two operations, details of which may be found by consulting Chapters 2, 3 and 4 of the Metal Can Defects Identification and Classification Manual of the Canadian Food Inspection Agency.

15.4.3.8.1 Non-Destructive (Visual) Inspection for External Defects

The closing machine operator, (includes seaming and sealing), closure supervisor or other competent person shall visually examine at least one container from each seaming, sealing, turret feed or closure head after closure has been completed at intervals not to exceed 30 minutes during operation of the closure machines. Each container shall be examined for the presence of externally visible defects, particularly at the seams, seals or closures. All observations shall be recorded.

When defects which may affect the integrity of the container or measurements outside of those specified for the closure are observed, immediate corrective action should be taken and recorded. All products from the time of the last inspection should be subjected to an evaluation to ensure that the integrity of the containers has not been compromised. Suspect containers should be set aside for further evaluation.

Additional visual examinations and non-destructive measurements shall be made and recorded following a jam, an adjustment to or start up following a prolonged shut-down of a closure operation.

Visual examination should be carried out using the hand as well as the eye. Sometimes it is easier to feel a defect rather than see it. By running the fingers around the seam both on the inside and the outside, it is possible to detect any roughness, unevenness or sharpness. A description of visual inspection of the can and the commonly observed defects in metal containers as well as the most probable causes can be found in Chapters 4 to 7 inclusive of the Metal Can Defects Identification and Classification Manual published by the Canadian Food Inspection Agency, and in various manuals published by the can manufacturers, closure machine manufacturers and manufacturers of sealing compounds. Processors are advised to consult these manuals and become familiar with their contents.

15.4.3.8.2 Destructive Examination of Closures

In addition to regular observations for container external defects by visual examinations, tear-down or destructive examinations and evaluations of the closures from at least one container from each seaming, sealing, turret feed or closure head shall be performed and recorded by a competent individual at the start-up of the closure operation and at intervals of sufficient frequency not to exceed four hours to ensure that the closure specifications are attained and maintained. Additional destructive examinations of closures shall be made immediately following a jam in a closure machine, after adjustment or after shut-down due to faulty seams or mechanical problems. Generally the closure performed by the canner is subject to the closest examination at this stage, however it is advisable to similarly examine and evaluate any closures made by the container manufacturer of at least one of the containers taken at any examination period.

Corrective action shall be taken when the inspection and evaluation reveals closures are not in compliance with the required specifications. All corrective actions shall be recorded.

More frequent visual examination and destructive evaluations of the closures should be carried out and recorded after corrective actions have been taken to ensure that the abnormalities or irregularities observed have been corrected.

The measurements and evaluations as well as their trends are important in the assessment of the closure integrity for control purposes. The recording of measurements and observations should permit the evaluation of trends, i.e., quality control charts.

15.4.3.8.2.1 Tear-Down Evaluation of Rigid Metal Can Double Seams

15.4.3.8.2.1.1 Round Cans

If the overlap is to be calculated using one of the formulas given below (i or ii), the double seam length (height or width) (w) should be measured prior to commencing the tear-down procedures. This should be measured at three points approximately 120° apart around the double seam, excluding the point of juncture with the side seam.

Other double seam measurements which can be made at the same time are used in the assessment of the seam quality:

a) countersink depth (A)
b) double seam thickness (S)

These should be made at the same points used for the double seam length.

All measurements should be recorded.

In the tear-down inspection of a double seam the following measurements should be made:

c) overlap
d) tightness rating
e) juncture rating for soldered side seam cans

Visual observation of the pressure ridge, where applicable, is useful in evaluation of double seam tightness.

In addition to these, especially when the overlap is to be calculated using one of the formulas, the following measurements should be made:

g) body hook length (BH)
h) cover hook length (CH)
i) end plate thickness (Te)
j) body plate thickness (Tb)
k) seam length (W)

In some instances the body hook and cover hook lengths are useful measurements in control of double seam quality and should be measured at least three separate points about the torn-down seam as described for the double seam length above.

Overlap

The overlap can be determined directly from a suitable cross-section cut of the double seam or by calculation.

The following formulas are used to calculate the overlap.

  1. Overlap = O = (CH + BH + Te) - W
  2. Percent Overlap = %O = [(BH + CH + Te - W) x 100] ÷ [W - (2Te + Tb)]

The overlap, body hook and cover hook lengths can be measured directly from a magnified cross-section image of a double seam with a seam scope and appropriate callipers or micrometers. The cross-section segments to be examined should be taken at least two or more places equally spaced around the double seam, excluding the juncture with the side seam.

In routine tear-down examination of a double seam both methods may be used, in that, a single cross-section is taken and the appropriate measurements made optically with the remainder of the double seam being torn down for further measurements and evaluations.

Juncture and tightness ratings

For the evaluation of both tightness and juncture ratings it is preferable that either a ten point or percentage rating system be used. All measurements and evaluations should be recorded.

The instructions and specifications of both the container and the sealing machine manufacturers should be accurately and continuously followed in the assessment of the measurements, their trends and evaluations as well as those of the appropriate agency having jurisdiction.

Guidance in the tear-down of a double seam is given in Chapter 4 of the Metal Can Defects Identification and Classification Manual published by the Canadian Food Inspection Agency.

15.4.3.8.2.1.2 Non-Round Cans

Such cans require special consideration. Container manufacturer's specifications should be consulted and followed to ensure that the appropriate measurements and evaluations are made at the critical locations.

15.4.3.8.2.2 Two-Piece Cans

The development of the two-piece can offers a number of advantages over the standard three-piece can. By eliminating the side seam and bottom double seam the possibility of leakers is diminished considerably. Another advantage of this two-piece can is the elimination of lead solder. The shallow drawn can is made by a single draw action and used for canned meats, and other products.

The taller drawn two-piece (DRD) can development is more recent than the shallow drawn. This can is made by multiple draw-redraw press actions and allows for the manufacture of standard sized food cans. There is no doubt that this container will make it easier for the food canner to achieve the hermetic seal; however can seam inspection and tear-down are still required on the packers end. Therefore, those defects attributed to the double seams in three-piece cans will be the same for two-piece cans.

15.4.3.8.2.3 Identification of Can Defects

See Chapter 7 of the Metal Can Defects Identification and Classification Manual published by the Canadian Food Inspection Agency.

15.4.3.8.2.4 Classification of Can Defects

See Chapter 5 of the Metal Can Defects Identification and Classification Manual published by the Canadian Food Inspection Agency.

15.4.3.8.3 Glass Containers

There are innumerable glass containers used in the food industry, however relatively few of these containers are used for products which require sterilization. There are three types that are suitable for the high temperature sterilization: lug, side seal and push on, twist off (PT). Glass containers, in addition to being subject to breakage due to impact or other mechanical reasons, are also subject to thermal shock.

15.4.3.8.3.1 Thermal Shock

Thermal shock is caused by temperature differences between the inside and outside of the wall of the jar, which results in different expansion rates of the glass in the wall, causing an internal stress. This stress can open up minute or even microscopic cracks or checks resulting in larger cracks and container failure. It is ironic that while thick-walled glass containers, such as milk and pop bottles, are more resistant to impact breakage, they are less resistant to thermal shock. Due to the extra thickness of the glass in the walls, there is more temperature differential between the inside and outside of the wall, causing greater internal stress. For this reason, glass containers to be used for heat processing should have relatively thin walls, and the walls and bottom of the container should be as close as possible to a uniform thickness.

Certain shapes of glass containers are more resistant to thermal shock than others. Generally, sharp contours and flat surfaces should be avoided in glass containers to be subjected to heat, since more failure occurs in these areas. There are also glass surface treatments such as stippling and knurling, which can, if incorporated into the design, help reduce failure due to thermal shock.

Chemical surface coatings which are often applied to glass containers to make them more resistant to brushing, also help resist thermal shock, since scratches and bruises on a glass container reduce its resistance to thermal shock.

15.4.3.8.3.2 Classification of Glass Container Defects
  1. Serious defects
    1. Any glass protrusions on either the inside or outside of the container. These could cause physical harm to people, but fortunately they occur very rarely in wide-mouthed food containers.
    2. Fire checks, including finish splits (an imperfection; crack or check going from surface to surface of glass container) and checks (an imperfection; a surface crack) in other parts of the container which will result in container failure during processing or loss of vacuum after processing.
    3. Out of round finish (an imperfection of non-roundness in glass containers), especially on side seal (pry-off) closures.
    4. Finish defects, including uneven or tilted finish, crizzles (an imperfection in the form of a multitude of fine surface fractures), chipped or damaged finish.
    5. Blowouts or thin area of side panel due to uneven distribution of glass in side walls.
    6. Variations in height or shape which are outside of specifications and which will cause failure of the closure.
  2. Minor defects
    1. Variations in height or shape which will not necessarily cause failure of closure.
    2. Swab marks (black smears) in glass (carry over from mold lubrication) - particularly noticeable in clear (flint or colourless) glass.
    3. Air bubbles, rattails or foreign material (such as unmelted silica) in glass.
    4. Slight variations in wall thickness.
    5. Deep baffle marks (mark or seam on the container resulting from a mold joint between blank mold and baffle plate) on the bottom of jars.
    6. Line overs on the finish which could result in a slow loss of vacuum.
    7. Scratched, bruised or scuffed containers.
    8. Dust or other foreign material which can be cleaned out by a jet of dry air (otherwise is a serious defect).
15.4.3.8.3.3 Identifying Problems in Glass Containers

On the bottom of each glass container there is a code put there by the glass manufacturer. This code is helpful in identifying problems. For example, defects such as "checks" in glass may occur only in one mold and vice versa, glass container failure occurring predominantly on one mold number indicates a manufacturing defect, whereas, if failure is distributed over all mold numbers, the problem is most likely due to handling or thermal shock.

Glass breakage due to impact or rough handling can usually be identified from that caused by thermal shock by the nature of the cracks. Impact will exhibit a cone-shaped break at point of impact with cracks radiating outwards. Thermal shock breakage usually results in a long curving crack with a mirror-like surface under reflected light. A small roundish hole near the bottom of the container holding viscous liquids is likely due to a "water hammer" action of the liquid on the container when it received a sharp knock. This occurs after processing, often during palletizing, or shipping, and can be corrected by gentler handling, better packaging, or by packing containers neck down.

15.4.3.8.3.4 Types of Closures for Glass Containers
  1. Twist off

    This is probably the most commonly used closure for glass food containers. The hermetic seal is formed between the top of the container finish and the ring of compound around the inside circumference of the cap. The cap is held in place by the internal vacuum in the container, and by metal lugs on the cap and corresponding thread on the container.

    There are several variations in shape of "Twist-off" caps, each designed for a specific need. However, the basic principles of each remain the same. The number of lugs varies to some extent depending on the size of the container "mouth". In most caps for sterilizing, there are four lugs, but on some larger containers there may be six lugs.

  2. Side seal or pry off closures

    Once widely used, this style of cap is now seen less and less. The hermetic seal is made by a gasket between the skirt of the cap and the side surface of the container finish. The cap is applied by pressure and held in place by internal vacuum.

  3. PT (push on, twist off) caps

    PT caps are so called because they are applied by downward pressure, yet are removed by twisting off. The hermetic seal in these caps is between the top and side surface of the container finish, and the gasket in the cap which is both in a ring around the inside circumference of the cap, and down the inside of the skirts of the cap.

    There are fine threads in the glass on the finish which embed in the compound of the skirt, together with internal vacuum hold the cover in place. Often PT caps are designed with a "pop up" centre which indicates that the jar has a proper vacuum by popping when opened.

15.4.3.8.3.5 Examination of Closures

Appropriate detailed examinations and tests shall be conducted by qualified personnel at intervals of sufficient frequency to ensure proper closing machine performance and consistently reliable hermetic seal production. In addition to routine inspection, a mechanical or electronic "dud detector" may be installed in the line, either before or after processing and cooling (preferable in both places). These machines work by removing any containers which have off-level caps, and those caps which do not have the proper concave inflection indicating the proper vacuum level in the container.

  1. Frequency of examination
    1. External examination at Capper: Straight Line Machines - six samples at random each 30 minutes. Rotary capper - one sample from each head each 30 minutes.
    2. Cap removal examination at capper: Straight Line Machines - three samples taken consecutively every four hours. Rotary capper - one sample per head every four hours.
    3. External examination after processing and cooling: six samples taken at random each 30 minutes.
    4. Cap removal examination after processing and cooling: six samples taken at random every four hours.
  2. External inspection

    Check external appearance of the cap for scratches, discoloration, and similar defects, and to be sure the cap is level, not cocked or tilted. There should be sufficient vacuum in the container to give the cap a concave appearance (more pronounced on processed, cooled containers). For "twist-off" caps, check for crushed lugs. A crushed lug occurs when the lug of the cap has been forced over the thread, and while the cap often appears to be sealed normally, looking under the skirt will reveal the actual position of the lugs.

    A measurement which can be made at this point, without destroying the seal is called the pull-up. This is defined as the distance between the leading edge of the cap lug, and the parting line (where finish moulds separate) in the jar finish, measured in 1/16 inch (1.6 mm). If the leading edge of the lug has not reached the parting line, the measurement is recorded in +1/16" (1.6 mm) while, if it has passed the parting line, it is recorded as - 1/16" (-1.6 mm). The pull-up value for each container and cover must be determined as different finishes, and different design of caps will give different desired values. Once the pull-up value desired is determined, a tolerance must be allowed to account for variation in caps and container finish.

    For PT caps check to make sure that the buttons of the "pop-up" feature are down indicating good vacuum.

  3. Cap removal inspection

    The checks done are as follows:

    1. Visual inspection same as for external inspection
    2. Cap security on twist-off caps
    3. Removal torque on twist-off and PT caps, using torque meter (this test is optional).
    4. Determination of vacuum and head space.
    5. Inspection of impression in gasket.
  4. Cap security - twist-off caps
    1. With a felt marking pen, make a vertical line along the parting line of the finish and into the cap.
    2. Take vacuum - using a vacuum gauge, or simply loosen cap by hand until vacuum is broken.
    3. Re-seal the closure until cap is finger tight - do not tighten with any force. Mark a line on container corresponding to line on cap.

    Cap security is the distance between the line indicating original position and the one showing new position recorded in 1/16" (1.6 mm). Record measurement as "+" if new line does not come up to original, and "-" if it passes original line. Proper security should be between +2/16" and +5/16" (3.2 mm and 8 mm).

  5. Removal torque

    This is defined as the foot-pounds (Joules) of torque required to remove either a Twist-off or PT cap and its use as a quality control procedure is optional. If used, there are torque-meters available especially designed for this purpose, and the acceptable torque range will be determined by each company, after consultation with the cap and glass suppliers.

    Removal torque can be affected by the presence of product in the hermetic seal (between the finish and the gasket of the cap) which can effectively cement the cap on. Too low a torque reading could be a result of poor security, loss of vacuum or where excessive tightening of cap has resulted in stripped lugs.

  6. Vacuum and head space

    The low acid foods packed in glass containers, are sealed with vacuum type closures. The resultant vacuum within the container plays a most important role in forming and maintaining the hermetic seal. Since head space is closely related to vacuum formation, its measurement is also taken during examination. There are three general methods of obtaining vacuum in glass containers:

    1. hot fill;
    2. mechanical means; and
    3. steam displacement.

    (See section 15.4.3.6 on methods of providing a vacuum in food container)

    It should be noted that mechanical vacuum cappers are used primarily on dry products. With cappers using steam displacement (steam flow type), the container is subjected to superheated steam which displaces the head space gases by a flushing action and becomes entrapped under the cap. Either straight line or rotary cappers are used with steam injection. Once the steam condenses, a partial vacuum begins to develop immediately after capping. The steam also softens the plastisol gasket within the closure which aids in good seal formation. In this respect, the formation of the hermetic seal on a glass container is perhaps less complicated than double seaming. Factors affecting vacuum formation will be noted in the following.

  7. Capper efficiency

    The most convenient, routine check on the vacuum efficiency of a steam flow capper is called the cold water vacuum check. The advantages of this simple test is, no special equipment is required, can be run prior to actual filling operations and also serves as a check on proper setting of the capper. To perform the cold water vacuum check, a jar to each rotary capper head or six jars from a straight line capper are filled with cold tap water to approximate head space which will be used with the product to be run. The capper is then allowed to warm up for approximately 5 to 10 minutes to the operating temperature and the normal steam setting followed by sealing of the jars. The jars are then opened and re-run through the capper and then checked for vacuum. The function of the initial run through the capper is to deaerate the water thereby providing a truer vacuum reading. The measured vacuum in most cases should be 22" Hg (-67.8 kPa) or more as recommended by the closure supplier. This cold water vacuum check shall be performed at the start up of a line, after a prolonged shutdown, at change-over from one container size to another, after a major jam and whenever significant vacuum fluctuations occur.

  8. Inspection of impression in gasket of cap

    Probably more than any other single examination the impression of the container finish into the gasket of the cap tells us the quality of the closure. The impression should be moderately deep, and uniform in both depth and width. Variations in depth can indicate a tilted or off-level finish, or dips in the finish of the container. Variations in width of the impression besides the above can indicate that the cover has been subjected to impact while the compound was soft. One should also check for cut-through of the gasket which could be a result of excessive tightening or pressure when applying the cover, or impact to the container or cap. Some gasket materials discolour during processing and discoloration may be more intense around a problem area such as a line or split in the finish, often helping locate potential container failure problems.

  9. Auxiliary equipment

    The function of auxiliary equipment, such as the head spacers, cocked-cap detectors and ejectors, and dud detectors, which may directly or indirectly affect the sealing of the container should be considered and reviewed by those individuals responsible for closure inspection.

15.4.3.8.3.6 Classification of Glass Closure Defects
  1. Serious defects
    1. Enamel failure on inside of cap, including no enamel, pinholes in enamel, scratches or poor adherence of enamel to cap.
    2. Gasket failure - poor distribution, overlapping, pinholes, no gasket or wrong gasket material.
    3. Lacquer failure on outside of caps when subjected to heat treatment as used in process.
    4. In coloured caps, failure of the colour to withstand the heat process, including blushing, fading, etc.
    5. Improper formation or depth of lugs on push on caps.
  2. Minor defects
    1. Scratched or scuffed outside surface.
    2. Minor changes in lacquer or colour during processing.
    3. Colour variation in coloured caps.
    4. Discolouration of gasket during processing.
    5. Error in printing if lithographed.
    6. Smears, dirt or foreign material on caps which can be cleaned in normal processing operation (otherwise is a serious defect).
15.4.3.8.4 Flexible Packages

Flexible packages for low acid foods provide a viable alternative to metal and glass containers. Commercial sterility is obtained by retorting using:

  1. water and superimposed air pressure processes;
  2. steam-air processes; or
  3. a continuous non-agitating process.

This section gives some general information on pouches and testing procedures. More specific information is given in the National Standard of Canada - Use of Flexible Laminated Pouches for Thermally Processed Foods prepared by the Canadian General Standards Board (Nov. 87). - CAN/C6SB-32.302-M87.

The basic construction of the retortable flexible package (pouch) consists of a three ply lamination.

  1. Inner layer

    A modified polyolefin (medium to high density polyethylene modified with polyisobutylene) or polypropylene (or ethylene-propylene blends) of 3 mil (76 micron) thickness is the inner heat sealant ply. Functions of this ply include heat sealability, compatibility (non reactive) with foods packed therein and strength.

  2. Middle layer

    Aluminum foil with a thickness of 1/3 mil (8.5 micron) is used as the primary barrier material. This ply possesses excellent vapour, gas and light barrier properties as well as superb heat transfer characteristics. The shape of the retortable pouch, i.e. high surface area to volume ratio and the aluminum foil are the two main reasons for reduced thermal processes when compared to those of foods packed in cans and glass containers.

  3. Outer layer

    The 1/2 mil (13 micron) of polyester (mylar) as the outer ply provides strength, printability and scuff resistance.

15.4.3.8.4.1 Package Integrity

Since the successful achievement of commercial sterility of foods, packed in flexible packages, is a function of heat application and prevention of re-infection by microorganisms in the package, its integrity must be carefully monitored. Leakers may result through inadequate seals or defective pouch body material. If flexible packages are to be accepted they must give the same degree of protection as metal and glass containers. Therefore, the failure or defect rate of not more than 0.01% should be applied to this type of package. To date, experience has indicated that this relatively low defect rate can be achieved if package, product and production is closely monitored.

15.4.3.8.4.2 Flexible Package Inspection
  1. Fusion

    The highest seal quality will always be obtained if the sealing surfaces are flat, clean and without creases or overlap of material. The package presently in use is a pouch with seals on all four sides, three of which are produced by the pouch manufacturer before the food product comes in contact with it. When filling the pouch, care must be exercised to avoid contaminating that area of the pouch which will subsequently form the closing seal. The sealing of the open side, after filling, is accomplished by a double-impulse sealing technique. To determine if the heat seal is satisfactory, the weld character is assessed using various tensile tests. Pouches destined for conventional handling should feature seals with 7 psi (48.3 kPa) or higher tensile strength values.

  2. Internal burst test

    This test for seal integrity has been generally accepted as a good overall measure of the ability of a package to withstand handling. The internal burst test has the advantage of detecting the weakest point of seal within the unsealed or cut and emptied pouch.

    An accepted or commercial internal burst criterion is 20 psi (138 kPa) for 30 seconds; however, variations of the burst test exist which are also utilized.

  3. Visual examinations

    The visual examination of pouches provides valuable information with regard to the package integrity. Not only is this test non-destructive but expensive equipment is not necessary. Defects, which can be identified with this examination include, heat creep, significant wrinkles, surface irregularities and entrapped matter in the seal area.

  4. Wrinkles

    Wrinkles may result in package leakers or allow the entry of spoilage organisms and thereby adversely affect package performance. Generally, true wrinkles are defined as a material fold on one seal surface, entrapped matter within the seal or an embossed surface. True wrinkles are not to be tolerated and are unacceptable. Minor wrinkles are acceptable, but if they are large enough to suspect contamination rejection is the alternative.

  5. Frequency of inspection

    Detailed inspections and tests shall be conducted by qualified persons at intervals of sufficient frequency to ensure proper closing machine performance and to assess the hermetic seal as per the following plan.

    Sampling SiteTestNo. of Samples per LotReject Criteria
    In-Process - After Pouch Formation Air Burst Bottom & Side Seal 6 consecutive per 30 minutes 1
    In-Process - After Closure Seal Air Burst Top Seal 6 consecutive per 30 minutes 1
    In-Process - After Closure Seal Visual for Defects 100% All Defective pkgs. removed
    Final Package - After Retorting Air Burst 13 random (6 bottom & Side) (7 - Top Seal) 1
    Final Package - After Retorting Visual for Defects 100% All Defective pkgs. removed
15.4.3.8.4.3 Action Required When Serious Defects are Found

Defects observed in incoming containers should result in a more widespread inspection of the received material before making a decision on acceptance or rejection of the lot.

If serious defects are found at any time after processing, the lots involved are to be placed under detention and the Area office informed by telephone. The Area office shall initiate a detailed investigation in consultation with headquarters, when required.

15.4.3.8.5 Product Retention for Closure Defects

If a seam or closure defect which may result in a loss of hermetic integrity is found upon routine examination (15.4.3.8), all containers sealed or closed between the discovery of the fault and the last satisfactory check should be identified and assessed.

15.4.3.9 Handling of Containers After Closure

At all times containers should be handled in a manner that protects the container and its closure from damage which may cause defects and subsequent microbial contamination. Design, operation and maintenance of container handling methods should be appropriate for the types of containers and materials used. Poorly designed or incorrectly operated container conveying and loading systems are known to cause damage. For example, cans which are scramble packed may suffer damage, even when water cushioned, when the level of the cans in a crate or the crateless retort reduces the efficiency of the cushion. Additionally, damage which may adversely affect integrity may be caused by poor alignment of the can feed mechanism or by the presence of floaters.

Care should also be taken with semi and fully automatic crate loading systems as well as in-feed conveyor systems to continuous sterilizers. The accumulation of stationary containers on moving conveyors should be avoided or kept to a minimum number as this can result in damage to the containers.

Semi-rigid and flexible containers may be prone to certain types of damage, e.g., snagging, tearing, cutting and flex-cracking. Containers having sharp edges should be avoided as they may cause damage to neighbouring containers. Semi-rigid and flexible containers should be handled with special care (see section 15.5).

15.4.3.10 Coding

Each container shall be labelled in a legible and permanent manner to identify the registered establishment, the meat product and the date on which the meat product is thermally processed or be marked with an identifying alphanumeric code which is permanent, legible and does not adversely affect the container integrity. (The code should be embossed or marked with indelible ink.)

The code mark shall identify the establishment in which the product was thermally processed, the product, the year and the day of the year when thermally processed. A key to the code marks employed must be made available to the inspector upon request. Further, when the establishment is not identified with its registration number, the operator must forward to the Meat Programs Division Registrar, through the inspector in charge the information that is used in the code mark to identify the establishment.

The code mark permits the identification and isolation of code lots during production, distribution and sale. Processors may find it useful to have a coding system which identifies production periods of less than 24 hours, say 8 hours or less and the particular line and/or sealing machine. The coding of containers in the manner described, supported by adequate processor records, can be very helpful in any investigation and may minimize the quantity of product subject to recall.

The outside of each shipping carton should indicate the code or codes of the canned food contained therein.

15.4.3.11 Washing

Where necessary, filled and sealed containers should be thoroughly washed before sterilization to remove grease, dirt and product from the outside of the container.

Not only is it more difficult to wash containers after sterilization, but it can also increase the risk of post-processing contamination.

15.4.4 Thermal Processing

15.4.4.1 General Considerations

15.4.4.1.1 Low-Acid Foods

Scheduled processes for low-acid foods must be established by competent persons having an expert knowledge of thermal processing and having adequate facilities for making such determinations. It is absolutely necessary to establish the required thermal process with accepted scientific methods. The type, range, and combination of variations encountered in commercial production shall be adequately provided for in establishing the scheduled process.

15.4.4.1.2 Acidified Low-Acid Foods

Scheduled processes for acidified low-acid foods must be established by competent persons having expert knowledge of acidification and thermal processing and having adequate facilities for making such determinations. It is absolutely necessary to establish the required acidification and thermal process with accepted scientific methods. The type, range, and combination of variations encountered in commercial production shall be adequately provided for in establishing the scheduled process.

The microbiological safety of acidified low-acid canned foods depends primarily upon the care and accuracy with which the entire process is carried out. Low-acid foods acidified to an equilibrium pH of greater than 4.6 must be processed to commercial sterility.

It must be realized that the thermal processing of low-acid canned foods as well as the acidification and thermal processing of acidified low-acid canned foods are very critical operations involving public health risks and appreciable losses of finished product if inadequately processed.

Instances have been known where improperly processed or sealed acidified low-acid canned foods have supported mould or other microbial growth which raised the product pH to above 4.6 and allowed the growth of Clostridium botulinum.

15.4.4.2 Establishing Scheduled Processes

15.4.4.2.1 Low-Acid Foods

The thermal process is established on that which is required to achieve at least a commercially sterile food product.

Due to the nature of the packaging materials used, flexible, and to some extent semi-rigid containers will change dimensions when exposed to applied physical stress. It is extremely important that the package dimensions, particularly the depth or thickness, be determined and controlled within specified limits. The dimensions and variations must be taken into account when determining the thermal process.

The thermal process shall be determined by carrying out heat penetration tests or other equivalent procedures. Acceptable scientific methods of establishing thermal processes shall include, where necessary, but not be limited to, microbial thermal death time (TDT) data, process calculations based on product heat penetration data, inoculated packs and incubation tests. The tests must be carried out under the most adverse conditions which are likely to be met under production conditions. For accurate determination of the heat penetration it is essential that the temperature at the slowest heating point in the container contents be monitored during the test. A sufficient number of trials must be carried out to ensure that all possible variations have been taken into account in establishing the required thermal process.

Because of the nature of the packaging materials used in flexible and semi-rigid containers, the container alone cannot generally be used to fix the heat sensing element at the desired point in the container contents. Therefore, other means may be required to ensure that the temperature sensing device is maintained at the desired point in the container contents during the entire test and without altering the heat penetration characteristics. During such testing the container dimensions, especially the thickness, must be controlled and known.

Because there may be unexpected deviations in heat transfer and product cooling characteristics, only persons having expert knowledge and experience in thermal processing should use laboratory simulators to develop scheduled processes. Results should, wherever possible, be verified in a production retort under normal conditions.

If accurate heat penetration data cannot be obtained, alternate methods (based on accepted scientific methods), may be used.

While compensations for moderate changes in container size for products showing simple heating curves can be derived by calculation (see 15.2.13.2), the effect of such changes, especially for products having broken heating curves (see 15.2.13.1)should be verified by heat penetration test or other equivalent methods.

The results of all tests and calculations used to determine the thermal process as well as those to establish the critical factors and their variation shall be incorporated into the scheduled process. For conventionally sterilized canned low-acid foods such a scheduled process shall include as a minimum the following data:

  • levels and types of preservatives, where applicable;
  • product and filling specifications, including any restrictions on ingredient changes or formulation including dimensional tolerances of solid ingredients;
  • container size (dimensions) and type;
  • container orientation and spacing in retort where appropriate;
  • ingoing weight of products including liquid where appropriate;
  • residual air content in the sealed container (flexible and semi-rigid containers);
  • pH of the product, where applicable;
  • minimum initial temperature;
  • water activity of the product, where applicable;
  • venting procedures, where applicable (these should be determined on fully loaded retorts only);
  • type and characteristics of the thermal processing system(s);
  • sterilization temperature;
  • sterilization time;
  • overpressure, where applicable;
  • cooling method, where applicable; and
  • date determined and source or processing authority.

Any changes in the product specifications, for example storage temperature of the finished product, must be evaluated as to their effect on the adequacy of the process. If the thermal process is found to be inadequate it must be re-established.

The residual air content of filled and sealed flexible and semi-rigid containers shall be kept to within specified limits to prevent excessive stressing of the seals during thermal processing and altering the container dimensions which can adversely affect the heat penetration.

Complete records concerning all aspects of the establishment of the scheduled process, including any associated incubation tests, shall be returned and readily available upon formal request by the inspector.

15.4.4.2.2 Acidified Low-Acid Foods

In addition to those factors specified in 15.4.4.2.1, the acidification and thermal processes required to achieve commercial sterility shall include the type of acidification process and equipment available as well as the time and conditions required to attain the desired equilibrium pH of all components of the product.

The process used to acidify the product must be determined by accurate pH measurements of all components to ensure that the desired equilibrium pH is achieved, if not prior to, at least at the end of the thermal treatment including cooling. Tests of the acidification procedure must be carried out under the most adverse conditions which are likely to be met in production. It is essential to carry out a sufficient number of tests to determine the effect of all possible variations.

Although the thermal treatment necessary to achieve commercial sterility of low-acid foods acidified to an equilibrium pH of 4.6 or less is considerably less severe than that for low-acid foods, the same principles as described for low-acid foods for determining an adequate thermal process shall be applied. Generally, bacterial spores will not outgrow in foods having an equilibrium pH below 4.6, hence the thermal treatment may only be required to kill mould, yeasts, vegetative bacterial cells and inactivate enzymes.

The results of the acidification and thermal process determinations together with established critical factors shall be incorporated into the scheduled process. In addition to those factors given in 15.4.4.2.1, pertinent details of the acidification process should be included.

A similar list of critical factors shall also be made for aseptically processed and packaged products. Such a list shall include the equipment and container sterilization requirements.

Product and filling specifications shall contain at least the following, where applicable: full recipe and preparation procedures; filling weights, head space, drained weight, temperature of product components at filling and consistency. Small deviations from the product and filling specifications which may seem negligible can cause serious deviations in the heat penetration characteristics of the product. For rotational sterilization, viscosity rather than the consistency can be an important factor and shall not only be specified but also controlled at the specified level.

The product code shall correspond clearly to a complete and accurate product specification containing, where applicable, at least the following:

  • full recipe and preparation procedures;
  • equilibrium pH of final product;
  • ingoing weight of product(s), including liquid where appropriate;
  • head space;
  • drained weight;
  • maximum dimensions of product components;
  • temperature of products at filling;
  • initial temperature;
  • consistency or viscosity; and
  • thermal process parameters.

Complete records concerning all aspects of the establishment of the scheduled process, including any associated incubation tests, shall be retained and readily available upon formal request by the inspector.

15.4.4.3 Acidification and Thermal Processing Conditions

Only properly determined scheduled processes must be used.

Scheduled processes including venting and acidification procedures, where appropriate, to be used for all products and container sizes being packed shall be posted in a conspicuous place near the processing equipment, so that it is readily available to the retort or processing system operator and to the inspector.

Acidification, thermal processing and associated processing operations shall be performed and supervised only by properly trained personnel. It is extremely important that both the acidification and thermal processing operations be carried out by operators under the supervision of personnel who understand the principles of acidification and thermal processing and who realize the need to follow instructions closely. Such personnel are required to have obtained a certificate of competency, having completed a thermal processing course approved by the Minister.

It is essential that all heat processing equipment shall be properly designed, correctly installed and carefully maintained.

15.4.4.3.1 Acidification

Acidified, fermented and pickled foods shall be so manufactured, processed and packaged that an equilibrium pH of 4.6 or lower is achieved within the time designated in the scheduled process and maintained.

Pertinent tests to monitor the acidification process at critical control points shall be carried out with sufficient frequency to ensure that the process is under control, i.e., as specified in the scheduled process.

Acidified low-acid foods which do not attain an equilibrium pH of 4.6 or lower shall be given a thermal process equivalent to that for low-acid foods.

15.4.4.3.2 Thermal Processing

Commercial sterility must be accomplished using such equipment and instruments as are needed to ensure that the scheduled process is achieved and to provide proper records.

Thermal processing shall be commenced as soon as possible after closing to avoid microbial growth or changes in heat transfer characteristics of the products. (As a general rule, the time between sealing the filled container and thermal processing should not exceed 60 minutes.) During breakdowns or when production is low, product may have to be processed in partially loaded retorts or pasteurizers in order to comply with the time limitation. In such instances, changes to the thermal processing parameters including venting procedures, where applicable, may be required.

The initial temperature of the contents of the coldest containers to be processed shall be determined and recorded with sufficient frequency to ensure that the temperature of the product is no lower than the minimum initial temperature specified in the scheduled process. In the case of hot fill operations, this would be one of the first containers to go into the retort, in the case of cold fill operations, one of the last to go into the retort. An appropriate sample container is selected, the contents are stirred and the temperature recorded using a thermometer. This is done at the time the retort is being closed for batch systems.

The thermal status of all containers shall be so indicated to avoid filled sealed containers bypassing the thermal process. This is particularly important in batch operations in which there is an ever present risk of large quantities of containers, i.e., in baskets, trucks, cars, crates, etc., bypassing the retorts or pasteurizers. Therefore, all retort baskets, etc., containing product for thermal processing or at least one of the containers on the top shall be plainly and conspicuously marked with a heat sensitive indicator, or by other effective means to provide visual evidence whether or not each unit has been thermally processed. When such heat indicators are attached to baskets, crates, etc., previously exposed indicators must be removed before refilling with unprocessed product.

The thermal process must be continuously monitored using the instruments as described in 15.4.5.2. Accurate records shall be made and maintained.

An accurate, clearly visible clock or other suitable timing device shall be installed in the thermal processing room and times should be read from this instrument and not from wristwatches, etc. Where two or more clocks or other timing devices are used in a thermal processing room they shall be synchronized. Temperature/time recording devices are not satisfactory for measuring the sterilization or thermal process times.

Commercial sterility of low-acid products acidified to a pH of 4.6 or less when thermally processed at atmospheric pressure, (hot-fill and hold), shall be accomplished using suitable equipment and the necessary instruments (see 15.4.5.2) to ensure that the scheduled process is achieved and to provide the proper records. Both temperature distribution and rates of heat transfer are important. Because of the variety of equipment available, reference should be made to the manufacturer of the equipment for details of installation, operation and control. Where the hot-fill and hold technique is used, it is important that all inner surfaces of the container reach the scheduled container sterilization temperature.

15.4.4.4 Critical Factors and the Application of the Scheduled Process

In addition to the minimum initial temperature of the product, sterilization or thermal process times and temperatures as well as overpressure, where applicable, other critical factors as specified by the process authority in the scheduled process shall be measured, controlled and recorded at intervals of sufficient frequency to ensure that these factors remain within the limits specified. Examples of these additional critical factors is given in 15.4.4.2.1 and 15.4.4.2.2.

Venting for steam retorting is critical, therefore time and temperature for venting operations as detailed in the vent schedule must be meticulously followed.

15.4.5 Equipment and Procedures for Acidification and Thermal Processing

15.4.5.1 Acidification Systems

For products that are to be acidified to an equilibrium pH at or below 4.6, it is essential that the manufacturer shall employ appropriate control procedures to ensure that the finished goods do not present a health hazard. Sufficient control, including frequent testing and records of results, shall be exercised so that the equilibrium pH values for acidified, fermented and pickled foods do not exceed 4.6. Such foods whose equilibrium pH is greater than 4.6 shall be treated as a low-acid food and shall be processed accordingly. Measurements of acidity of foods in-process may be made by potentiometric methods, titratable acidity, or in certain instances colorimetric methods. In-process measurements by titration or colorimetry shall be related to the finished equilibrium pH. If the finished equilibrium pH is 4.0, or below, the acidity of the final product may be determined by any suitable method. If the finished equilibrium pH of the food is above 4.0 the measurement of the finished equilibrium pH shall be by a potentiometric method.

15.4.5.1.1 Direct Acidification

Procedures for acidification to attain acceptable pH levels in the food include, but are not limited to the following:

  1. blanching of the food ingredients in acidified aqueous solutions;
  2. immersion of the blanched food in acid solutions - although immersion of food in an acid solution is a satisfactory method for acidification, care should be taken to assure that the acid concentration is properly maintained;
  3. direct batch acidification which is generally achieved by adding a known amount of an acid solution to a specified amount of food during acidification;
  4. direct addition of a predetermined amount of acid to individual containers during production; for this, liquid acids are generally more effective than solid or pelleted acids - care should be taken to ensure that the proper amount of acid is added to each container and distributed uniformly;
  5. addition of acid foods to low-acid foods in controlled proportions to conform to specific formulations; and
  6. the time for equilibrium and buffering effects should always be taken into account - in all cases, equilibration should be completed by the termination of the thermal processing.
15.4.5.1.2 Acidification by Fermentation and Salt Curing

Temperature, salt concentration and acidity are important factors in controlling the fermentation and salt curing of foods. The progress and control of the fermentation shall be monitored by appropriate tests. The concentration of salt in the brine shall be determined by a chemical or physical test, at sufficient intervals to assure the control of the fermentation. The progress of the fermentation shall be monitored by pH measurements or acid/base titrations or both according to methods acceptable to the process authority, at sufficient intervals to assure the control of the fermentation. The concentration of salt or acid in the brine in bulk tanks containing salt stock may become significantly diluted and therefore should be routinely checked and adjusted as necessary.

15.4.5.2 Instruments and Controls Common to Different Thermal Processing Systems

15.4.5.2.1 Indicating Thermometer

Each retort, product sterilizer or pasteurizer shall be equipped with at least one indicating thermometer. The mercury-in-glass (MIG) thermometer is recognized as the most reliable temperature indicating instrument at the present time. An alternative instrument having equal accuracy, precision and reliability may be used subject to the approval of the Canadian Food Inspection Agency. The MIG thermometer shall have divisions that are easily readable to 0.5°C (1°F) and whose scale does not contain more than 4°C per centimetre (17°F per inch) of graduated scale. Thermometers shall be tested for accuracy against a known accurate standard thermometer. This should be done in steam or water as appropriate and in a similar aspect or position to that in which it is installed in the retort. Such tests shall be performed just prior to installation, and at least once a year thereafter or more frequently as may be necessary to ensure their accuracy. A dated record of such tests should be kept. A thermometer that deviates by more than 0.5°C (1°F) from the standard thermometer reading shall be replaced. A daily inspection of MIG thermometers shall be made to detect and replace thermometers with divided mercury columns or other defects which may impede their accuracy. If alternate devices are used they shall be subject to the same testing and standardization as described for MIG thermometers.

The indicating thermometer shall be located so as to be accurately and easily read, since these are the reference instruments for indicating the processing temperature, not the recording thermometers.

15.4.5.2.2 Temperature/Time Recording Devices

Each retort, product sterilizer or pasteurizer shall be equipped with at least one temperature/time recording device. This may be combined with a steam controller, i.e., a temperature controlling and recording instrument. It is important that the correct chart be used for each device. The chart shall have a working scale of not more than 12°C to the centimetre (55°F to the inch) within the range of 10°C (18°F) of the sterilizing or process temperature, and the chart graduations shall not exceed 1°C within 6°C of the processing temperature. The recorder shall be calibrated so that the temperature indicated is not greater than the temperature of the indicating thermometer. A means of preventing unauthorized changes in the adjustment shall be provided. It is important that the chart be used to provide a permanent record of the thermal processing temperature in relation to time. The timing device shall be accurate, reliable and checked as often as necessary to ensure that its accuracy and reliability is maintained.

15.4.5.2.3 Pressure Gauge

Each pressure vessel or retort shall be equipped with an accurate and reliable pressure gauge. The gauge shall be checked for accuracy at least once a year. The gauge shall be set so as to read zero at the prevailing atmospheric pressure. The scale shall have a range such that the safe working pressure of the retort is approximately two-thirds of the full scale and be graduated into divisions not greater than 14 kPa (2 psi). The gauge dial shall be large enough to be easily and accurately read (diameter not less than 10 cm or 4 in). The instrument may be connected to the retort by means of a gauge cock and siphon.

15.4.5.2.4 Steam Controller

Each retort, product sterilizer or pasteurizer in which steam is the source of heat shall be equipped with a steam controller to maintain the desired temperature. This may be a recording-controlling instrument when combined with a recording thermometer.

15.4.5.2.5 Pressure Safety Valve

Each retort shall be equipped with a pressure safety valve having a capacity sufficient to prevent undesired increases in the retort pressure. Such valves shall be of a type and installed in a manner approved by the agency having jurisdiction. If a retort is used only at atmospheric pressure, a pressure safety valve may not be necessary.

15.4.5.2.6 Timing Devices

These shall be checked to ensure accuracy as often as necessary.

15.4.5.3 Pressure Processing in Steam

15.4.5.3.1 Batch Still Retorts
15.4.5.3.1.1 Common Instruments and Controls

All retorts shall be equipped with the instruments and devices described in 15.4.5.2.1 to 15.4.5.2.5, inclusive.

Bulb sheaths of indicating thermometers and probes of temperature recording devices shall be installed either within the retort shell or in external wells attached to the retort. External wells should be connected to the retort through at least a 19 mm (3/4 in) diameter opening and shall be equipped with an adequate (1.6 mm or 1/16 in, or larger) bleeder opening so located as to provide a constant flow of steam past the length of the thermometer bulb or recorder probe. The bleeder for external wells shall emit steam continuously during the entire thermal processing period. Thermometers shall be installed where they can be accurately and easily read.

15.4.5.3.1.2 Steam Inlet

The steam inlet to each retort shall be large enough to provide sufficient steam for proper operation of the retort, and shall enter at a suitable point (generally opposite) to facilitate air removal during venting.

15.4.5.3.1.3 Crate Supports

A bottom crate support shall be employed in vertical retorts so as not to substantially affect either venting or steam distribution. Baffle plates shall not be used in the bottom of retorts. Centring guides shall be installed in vertical retorts to ensure adequate clearance between the retort crate and the retort wall.

15.4.5.3.1.4 Steam Spreaders

Perforated steam spreaders, if used, shall be checked regularly to ensure they are not blocked or otherwise inoperative. Horizontal still retorts shall be equipped with perforated steam spreaders that extend for the full length of the retort. In vertical still retorts perforated steam spreaders, if used, shall be in the form of a cross or coil. The number of perforations in spreaders for both horizontal and vertical still retorts shall be such that the total cross-sectional area of the perforations is equal to 1.5 to 2 times the cross-sectional area of the smallest part of the steam inlet line.

15.4.5.3.1.5 Bleeders for Condensate Removal

Bleeders shall be of a suitable size, e.g.mm (1/8 in) and location and shall be fully open during the entire thermal process, including the come-up-time. In retorts having top steam inlet and bottom venting, a bleeder or other suitable device shall be installed in the bottom of the retort to continuously remove condensate. All bleeders shall be arranged in such a way that the operator can observe that they are functioning properly. Bleeders are not part of the venting system.

15.4.5.3.1.6 Stacking Equipment

Crates, trays, gondolas, dividers, etc., for holding product containers shall be so constructed that steam can adequately be circulated around the containers during the venting, come-up and sterilization times.

15.4.5.3.1.7 Vents and Venting Systems

To ensure adequate removal of air from the retort and uniform temperature distribution during thermal processing, venting schedules shall be established with correctly applied temperature distribution studies. Such studies shall be carried out by persons competent and experienced in thermal processing. Records of all studies shall be made available to the inspector upon request and maintained. Once established, the venting schedule shall be posted adjacent to the applicable equipment at the processor's location.

  1. Vents shall be installed in such a way that air is removed from the retort before timing of the process is started.
  2. Vents shall be controlled by gate, plug cock or other adequate type valves and must be fully open to permit rapid discharge of air from the retort during the venting period.
  3. Vents shall not be connected directly to a closed drain system. If the overflow line is used as a vent, there shall be an atmospheric break in the line before it connects to a closed drain.
  4. The vent should be located in that portion of the retort opposite the steam inlet; for example steam inlet in bottom portion and vent in top portion.
  5. The total cross-section area of steam vent outlets shall always be greater than the cross-section area of the steam inlet.

When a retort manifold connects several vent pipes from horizontal single retorts, it shall be controlled by a gate, plug cock or other adequate type of valve. The retort manifold shall be of a size such that the cross sectional area of the pipe is larger than the total cross sectional area of all connecting vents.

The discharge shall not be directly connected to a closed drain without an atmospheric break in the line. A manifold header connecting vents or manifolds from several still retorts shall lead to the atmosphere. The manifold header shall not be controlled by a valve and shall be of a size such that the cross-sectional area is at least equal to the total cross-sectional area of all connecting retort manifold pipes from all retorts which could be venting simultaneously.

Timing of the process shall not begin until the retort has been properly vented and the processing temperature has been reached.

15.4.5.3.1.8 Venting Considerations

The suggested venting method described in the following pages implies that the steam valve is also wide open. Using a steam controller to regulate the supply of steam before the vent temperature requirement has been reached invalidates the concept of venting. This is because the control valve will oscillate between fully open and fully closed (unless the retort controller is proportional). This means that the flow of steam will shut off intermittently during the vent. Manual throttling of the bypass reduces the flow of steam but does not shut it off. If such throttling is required temperature distribution studies shall be undertaken to prove the vent effectiveness.

Example: When it is suggested that vent valves be wide open for at least five minutes and to at least 107°C (225°F) it means that timing commences when steam is turned on and if at the end of five minutes, the temperature equals or exceeds 107°C (225°F), then the vent schedule has been satisfied.

The following vents and venting procedures are to provide guidance only and shall always be verified in practice.

If dividers are used in the retort baskets the following venting methods are not valid. Temperature distribution tests are required to determine the proper venting procedures.

15.4.5.3.1.8.1 Venting Horizontal Retorts

  1. Venting through multiple 25 mm (1 in) vents discharging to atmosphere

    Specifications: There should be one 25 mm (1 in) vent equipped with a gate or plug cock valve for discharging to the atmosphere for every 1.5 m (5 ft) of retort length and the end vents should not be over 0.75 m (2.5 ft) from the ends of the retort.

    Venting method: Vent valves should be wide open for at least 5 minutes and to a retort temperature of at least 107°C (225°F) or for at least 7 minutes and a temperature of 104.5°C (220°F).

  2. Venting through multiple 25 mm (1 in) vents discharging through a manifold to atmosphere

    Specifications: There should be one 25 mm (1 in) vent for every 1.5 m (5 ft) of retort length and the end vents should not be over 0.75 m (2.5 ft) from the ends of the retort. For retorts less than 4.5 m (15 ft) in length the inside diameter (ID) of the manifold should be not less than 64 mm (2.5 in) and for retorts whose length is 4.5 m (15 ft) or greater the ID should be at least 75 mm (3 in).

    Venting method: The manifold valve should be wide open for at least 6 minutes and to a retort temperature of 107°C (225°F), or for at least 8 minutes and to a temperature of 104.5°C (220°F).

  3. Venting through water spreaders

    Specifications: The inside diameter (ID) of the water inlet, vent pipe and vent valve for retorts less than 4.5 m (15 ft) in length should be not less than 50 mm (2 in) and for retorts 4.5 m (15 ft) or greater in length they should be not less than 64 mm (2.5 in). The size (ID) of the water spreader for retorts less than 4.5 m (15 ft) in length should be not less than 40 mm (1.5 in) and for retorts 4.5 m (15 ft) or greater in length they should not be less than 50 mm (2 in).

    Venting method: The water spreader vent gate or plug cock valve should be wide open for at least 5 minutes and to a retort temperature of at least 107°C (225°F), or for at least 7 minutes and to at least 104.5°C (220°F).

  4. Venting through a single 64 mm (2.5 in) top vent (for retorts not exceeding 4.5 m (15 ft) in length)

    Specifications: The vent should have an ID of at least 64 mm (2.5 in) and be equipped with at least a 64 mm (2.5 in) gate or plug cock valve and be located within 0.6 m (2 ft) of the centre of the retort.

    Venting method: The vent gate or plug cock valve should be wide open for at least 4 minutes and to a retort temperature of at least 104.5°C (220°F).

15.4.5.3.1.8.2 Venting Vertical Retorts

  1. Venting through a 40 mm (1.5 in) overflow

    Specifications: The overflow pipe should have an ID of at least 40 mm (1.5 in) equipped with at least a 40 mm (1.5 in) gate or plug cock valve and with not more than 1.8 m (6 ft) of 40 mm (1.5 in) pipe beyond the valve before the break to the atmosphere or to a manifold header.

    Venting method: The vent gate or plug cock valve should be wide open for at least 4 minutes and to a retort temperature of 103.5°C (218°F), or for at least 5 minutes and to at least 101.5°C (215°F).

  2. Venting through a single 25 mm (1 in) side or top vent

    Specifications: The vent in the lid or top side should have an ID of at least 25 mm (1 in) and be equipped with a 25 mm (1 in) gate or plug cock valve and discharge directly into the atmosphere or to a manifold header.

    Venting method: The vent gate or plug cock valve should be wide open for at least 5 minutes and to a retort temperature of at least 110°C (230°F) or for at least 7 minutes and to at least 104.5°C (220°F).

Other installations and operating procedures which deviate from the foregoing may be used provided that there is evidence that adequate venting of the air is accomplished. This would be determined by a heat distribution test, and the data obtained should be kept on file by the processor.

15.4.5.3.1.9 Air Inlets

Retorts using air for pressure cooling shall be equipped with an adequate tight closing valve and piping arrangement on air line to prevent leakage of air into the retort during processing.

15.4.5.3.2 Batch Agitating Retorts

All retorts shall be equipped with the instruments and devices described in 15.4.5.2.1 to 15.4.5.2.5, inclusive.

15.4.5.3.2.1 Steam Inlet (see 15.4.5.3.1.2)
15.4.5.3.2.2 Steam Spreaders (see 15.4.5.3.1.4)
15.4.5.3.2.3 Bleeders and Condensate Removal (see 15.4.5.3.1.5)

At the time the steam is turned on, the drain shall be opened for a time sufficient to remove steam condensate from the retort and provision should be made for continuous drainage of condensate during the retort operation. The bleeders in the bottom of the shell serve as an indicator of continuous condensate removal. The retort operator shall observe and periodically record how this bleeder is functioning.

15.4.5.3.2.4 Stacking Equipment (see 15.4.5.3.1.6)
15.4.5.3.2.5 Vents (see 15.4.5.3.1.7)
15.4.5.3.2.6 Air Inlets (see 15.4.5.3.1.9)
15.4.5.3.2.7 Retort or Reel Speed Timing

The rotational speed of the retort or reel is critical and shall be specified in the scheduled process. The speed shall be adjusted and recorded when the retort is started, and at intervals of sufficient frequency to insure that the retort speed is maintained as specified in the scheduled process. If a change of speed inadvertently occurs, this shall be recorded together with corrective action taken. Additionally, a recording tachometer may be used to provide a continuous record of the speed. The speed shall be checked against a stop watch at least once per shift. A means of preventing unauthorized speed changes on retorts shall be provided.

15.4.5.3.3 Continuous Agitating Retorts (e.g. FMC)

All retorts shall be equipped with the instruments and devices described in 15.4.5.2.1 to 15.4.5.2.5, inclusive.

15.4.5.3.3.1 Steam Inlet (see 15.4.5.3.1.2)
15.4.5.3.3.2 Steam Spreaders (see 15.4.5.3.1.4)
15.4.5.3.3.3 Bleeders and Condensate Removal (see 15.4.5.3.2.3)
15.4.5.3.3.4 Vents (see 15.4.5.3.1.7)
15.4.5.3.3.5 Retort and Reel Speed Timing (see 15.4.5.3.2.7)
15.4.5.3.4 Hydrostatic Retorts (e.g. Stork)
15.4.5.3.4.1 Indicating Thermometers (see 15.4.5.2.1)

Thermometers shall be located in the steam dome near the steam/water interface and preferably also at the top of the dome. Where the scheduled process specifies maintenance of particular temperatures of water in the hydrostatic water legs, at least one indicating thermometer shall be located in each hydrostatic water leg so that it can accurately measure water temperature and be easily read.

15.4.5.3.4.2 Temperature/Time Recording Device (see 15.4.5.2.2)

The temperature recorder probe shall be installed either within the steam dome or in a well attached to the dome. Additional temperature recorder probes shall be installed in the hydrostatic water legs if the scheduled process specifies maintenance of particular temperatures in these hydrostatic water legs.

15.4.5.3.4.3 Pressure Gauges (see 15.4.5.2.3)
15.4.5.3.4.4 Steam Controllers (see 15.4.5.2.4)
15.4.5.3.4.5 Steam Inlet (see 15.4.5.3.1.2)
15.4.5.3.4.6 Bleeders

Bleeders shall be of suitable size, e.g., 3 mm (1/8 in) and location and shall be fully open during the entire process, including the come-up-time and shall be suitably located in the steam chamber or chambers to remove air which may enter with the steam.

15.4.5.3.4.7 Venting

Before the start of processing operations, the retort steam chamber or chambers shall be vented to ensure removal of air.

15.4.5.3.4.8 Conveyor Speed

The speed of the container conveyor shall be specified in the scheduled process and shall be determined with an accurate stop watch, and recorded at the start of processing and at intervals of sufficient frequency to insure that the conveyor speed is maintained as specified. An automatic device should be used to stop the conveyor and provide warning when the temperature drops below that specified in the scheduled process. A means of preventing unauthorized speed changes shall be provided. Additionally a recording device may be used to provide a continuous record of the speed.

15.4.5.4 Pressure Processing in Water

15.4.5.4.1 Batch Still Retorts
15.4.5.4.1.1 Indicating Thermometer (see 15.4.5.2.1)

Bulbs of indicating thermometers shall be located in such a position that they are beneath the surface of the water throughout the process. On horizontal retorts this shall be in the side at the centre, and the thermometer bulbs shall be inserted directly into the retort shell. In both vertical and horizontal retorts, the thermometer bulbs shall extend directly into the water for a minimum of at least 5 cm (2 in).

15.4.5.4.1.2 Temperature/Time Recording Device (see 15.4.5.2.2)

When the retort is equipped with a temperature recording device, the recording thermometer bulb shall be at a location adjacent to the indicating thermometer or at a location which adequately represents the lowest temperature in the retort. In any case, care shall be taken that the steam does not strike the controller bulb directly.

15.4.5.4.1.3 Pressure Gauge (see 15.4.5.2.3)
15.4.5.4.1.4 Pressure Safety Valve (see 15.4.5.2.5)
15.4.5.4.1.5 Pressure Control Valve

In addition to the pressure safety valve an adjustable pressure control valve of a capacity sufficient to prevent undesired increases in retort pressure, even when the water valve is wide open, shall be installed in the overflow line. This valve also controls the maximum water level in the retort. The valve shall be suitably screened to prevent blockage by floating containers or debris.

15.4.5.4.1.6 Pressure Recorder

A pressure recorder device is needed and may be combined with a pressure controller.

15.4.5.4.1.7 Steam Controller (see 15.4.5.2.4)
15.4.5.4.1.8 Steam Inlet

The steam inlet shall be large enough to provide sufficient steam for proper operation of the retort.

15.4.5.4.1.9 Steam Distribution (see 15.4.5.3.1.3)

Steam shall be distributed from the bottom of the retort, unless the steam is fed to the water during recirculation outside the retort, in a manner to provide uniform heat distribution throughout the retort.

15.4.5.4.1.10 Crate Supports (see 15.4.5.3.1.3)
15.4.5.4.1.11 Stacking Equipment

Crates, trays, gondolas, divider plates, etc. when used for holding product containers shall be so constructed that the heating water can adequately circulate around the containers during the coming-up and sterilization times. Special equipment will be required to ensure that the thickness of filled flexible containers will not exceed that specified in the scheduled process and that they will not become displaced and overlap one another during the thermal process.

15.4.5.4.1.12 Drain Valve

A screened, non-clogging, water-tight valve should be used.

15.4.5.4.1.13 Water Level

There shall be a means of determining the water level in the retort during operation (e.g. by using a water gauge glass or petcock(s)). Water shall adequately cover the top layer of containers during the entire coming-up, sterilizing and cooling periods. This water level shall be at least 15 cm (6 in) over the top layer of product containers in the retort.

15.4.5.4.1.14 Air Supply and Controls

In both horizontal and vertical still retorts for pressure processing in water, a means shall be provided for introducing compressed air at the proper pressure and rate. The retort pressure shall be controlled by an automatic pressure control unit. A non-return valve shall be provided in the air supply line to prevent water from entering the system. Air or water circulation shall be maintained continuously during the coming-up-time, processing and cooling periods. Air is usually introduced with steam to prevent "steam hammer". If air is used to promote circulation it shall be introduced into the steam line at a point between the retort and the steam control valve at the bottom of the retort.

15.4.5.4.1.15 Cooling Water Entry

In retorts processing glass jars the cooling water should be introduced in a manner which avoids direct impingement on the jars, in order to prevent breakage by thermal shock.

15.4.5.4.1.16 Retort Head Space

The air pressure in the head space of the retort shall be controlled throughout the process.

15.4.5.4.1.17 Water Circulation

All water circulations systems, whether by pumps or air, used for heat distribution shall be installed in such a manner that an even temperature distribution throughout the retort is maintained. Checks for correct operation shall be made during each processing cycle, for example, alarm systems to indicate malfunction of water circulation.

15.4.5.4.2 Batch Agitating Retorts
15.4.5.4.2.1 Indicating Thermometer (see 15.4.5.2.1 and 15.4.5.3.1.1)
15.4.5.4.2.2 Temperature/Time Recording Device (see 15.4.5.2.2)

The recording thermometer probe shall be located adjacent to the bulb of the indicating thermometer.

15.4.5.4.2.3 Pressure Gauges (see 15.4.5.2.3)
15.4.5.4.2.4 Pressure Safety Valve (see 15.4.5.2.5)
15.4.5.4.2.5 Pressure Control Valve (see 15.4.5.4.1.5)
15.4.5.4.2.6 Pressure Recorder (see 15.4.5.4.1.6)
15.4.5.4.2.7 Steam Controller (see 15.4.5.2.4)
15.4.5.4.2.8 Steam Inlet (see 15.4.5.3.1.2)
15.4.5.4.2.9 Steam Spreader (see 15.4.5.3.1.1)
15.4.5.4.2.10 Drain Valve (see 15.4.5.4.1.12)
15.4.5.4.2.11 Water Level Indicator (see 15.4.5.4.1.13)
15.4.5.4.2.12 Air Supply and Controls (see 15.4.5.4.1.14)
15.4.5.4.2.13 Cooling Water Entry (see 15.4.5.4.1.15)
15.4.5.4.2.14 Water Circulation (see 15.4.5.4.1.17)
15.4.5.4.2.15 Retort Speed Timing (see 15.4.5.3.2.7)

15.4.5.5 Pressure Processing in Steam-Air Mixtures (e.g. Lagarde retort)

Both the temperature distribution and the rates of heat transfer are critically important in the operation of steam-air retorts. There shall be a means of circulating the steam-air mixtures to prevent formation of low temperature pockets. The circulating system used shall provide acceptable heat distribution as established by adequate tests. The operation of the processing system shall be the same as that required by the scheduled process. A recording pressure controller shall control the air inlet and the steam-air mixture outlet. Because of the variety of existing designs, reference should be made to the equipment manufacturer and to the agency having jurisdiction for details of installation, operation and control. Some items of equipment may be common to those already in this code and those standards given may be relevant.

15.4.5.6 Aseptic Processing and Packaging Systems

15.4.5.6.1 Product Sterilization Equipment and Operation
15.4.5.6.1.1 Temperature Indicating Device (see 15.4.5.2.1)

The device shall be installed in the product holding section outlet in such a way that it does not interfere with product flow.

15.4.5.6.1.2 Temperature Recording Device (see 15.4.5.2.2)

The temperature sensor shall be located in the sterilized product at the holding section outlet in such a way that it does not interfere with the product flow.

15.4.5.6.1.3 Temperature Recorder-controller

An accurate temperature recorder-controller shall be located in the product sterilizer at the final heater outlet in such a way as not to interfere with product flow. It shall be capable of ensuring that the desired product sterilization temperature is maintained.

15.4.5.6.1.4 Product-to-Product Regenerators

Where a product-to-product regenerator is used to heat the cold unsterilized product entering the sterilizer by means of a heat exchange system, it shall be designed, operated and controlled so that the pressure of the sterilized product in the regenerator is greater than the pressure of any unsterilized product. This ensures that any leakage in the regenerator will be from the sterilized product into the unsterilized product.

15.4.5.6.1.5 Differential Pressure Recorder-controller

Where a product-to-product regenerator is used, there shall be an accurate differential pressure recorder-controller installed on the regenerator. The scale divisions shall be easily readable and shall not exceed 14 kPa (2 psi) on a working scale of not more than 140 kPa (20 psi). The controller shall be tested for accuracy against a known accurate standard pressure indicator, upon installation and at least once every three months of operation thereafter or more frequently as may be necessary to ensure its accuracy. One pressure sensor shall be installed at the sterilized product regenerator outlet, and the other pressure sensor shall be installed at the unsterilized product regenerator inlet.

15.4.5.6.1.6 Metering Pump

A metering pump shall be located upstream from the holding section and shall be operated consistently to maintain the required rate of product flow. A means of preventing unauthorized speed changes shall be provided. The product flow rate, which is the critical factor controlling the sterilization holding time, shall be checked with sufficient frequency to ensure that it is as specified in the scheduled process.

15.4.5.6.1.7 Product-holding Section

The product sterilizer holding section shall be designed to give continuous holding of the product, including particulates, for at least the minimum holding time specified in the scheduled process. It shall be sloped upward at least 2.0 cm/m (0.25 in per foot). The holding section shall be designed so that no portion between the product inlet and the product outlet can be heated.

15.4.5.6.1.8 Start Up

Prior to the start of aseptic processing operations, the product sterilizer shall be brought to a condition of commercial sterility.

15.4.5.6.1.9 Temperature Drop in Product Holding Section

When product temperature in the holding section drops below the temperature specified in the scheduled process, the product in the holding section and any downstream portions affected shall be diverted to recirculation or waste and the system returned to a condition of commercial sterility before flow is resumed to the filler.

15.4.5.6.1.10 Loss of Proper Pressures in the Regenerator

Where a regenerator is used the product may lose sterility whenever the pressure of sterilized product in the regenerator is less than 7 kPa (1 psi) greater than the pressure of unsterilized product. Product flow shall be directed either to waste or recirculated until the cause of the improper pressure relationship has been corrected and the affected system(s) has been returned to a condition of commercial sterility.

15.4.5.6.2 Product Container Sterilization, Filling and Closing Operations
15.4.5.6.2.1 Recording Devices

The systems for container and closure sterilization, as well as filling and closing shall be instrumented to show that the scheduled conditions are achieved and maintained. During pre-sterilization as well as production, automatic recording devices shall be used to record, where applicable, the sterilization media flow rates and/or temperatures. Where a batch system is used for container sterilization, the sterilization conditions shall be recorded.

15.4.5.6.2.2 Timing Method(s)

A method(s) shall be used either to give the retention time of containers, and closure if applicable, as specified in the scheduled process, or to control the sterilization cycle at the rate as specified in the scheduled process. A means of preventing unauthorized speed changes shall be provided.

15.4.5.6.2.3 Start Up

Prior to the start of filling, both the container and closure sterilizing system and the product filling and closing system shall be brought to a condition of commercial sterility.

15.4.5.6.2.4 Loss of Sterility

In the event of loss of sterility, the system(s) shall be returned to a condition of commercial sterility before resuming operations.

15.4.5.7 Flame Sterilizers, Equipment and Procedures

The container conveyor speed shall be specified in the scheduled process. The container conveyor speed shall be measured and recorded at the start of operations and at intervals of sufficient frequency to ensure that the conveyor speed is as specified in the scheduled process. Alternatively, a recording tachometer may be used to provide a continuous record of the speed. Speed shall be checked against a stop watch at least once per shift. A means of preventing unauthorized speed changes on the conveyor shall be provided. The surface temperature of at least one container from each conveyor channel shall be measured and recorded at the end of the pre-heat section and at the end of the holding period at intervals of sufficient frequency to ensure that the temperatures specified in the scheduled process are maintained.

15.4.5.8 Other Systems

Systems for the thermal processing of low-acid foods and acidified low-acid foods in hermetically sealed containers shall conform to the applicable requirements of this chapter and shall ensure that the methods and control used for the manufacture, processing and/or packing of such foods are operated and administered in a manner adequate to achieve commercial sterility.

15.4.6 Evaluation of Deviation in Thermal Processing

Whenever the in-process monitoring records, processor check or other means disclose that a low-acid food or container system has received a thermal or sterilization treatment less than that stipulated in the scheduled process, or when any critical factor does not comply with the requirements for that factor as specified in the scheduled process, it shall be considered a deviation in processing or process deviations. Deviations in processing (or process deviations) shall be handled in accordance with the following paragraphs:

  1. Deviations identified in process:

    If a deviation is noted at anytime before the completion of the intended scheduled process, the processor shall:

    1. immediately reprocess the product using the full scheduled process; or
    2. use an appropriate alternate scheduled process provided such a scheduled process has been established in accordance with section 15.4.4. This alternate process shall be made readily available to the inspector upon his request; or
    3. hold the product involved and have the deviation evaluated by competent processing expert(s) in accordance with procedures recognized as being adequate to detect any hazard to public health.

    Upon completion of the evaluation, a record shall be made of the handling of each deviation. Such records shall include, at a minimum, the appropriate processing and production records, a full description of the corrective actions taken, the evaluation report and the disposition of the affected product. Such records shall be maintained in a separate file or log, and be made available to the inspector upon request.

  2. Deviations identified through record review:

    Whenever a deviation is noted during review of the processing and production records, the processor shall hold the product involved and have the deviation evaluated by competent processing expert(s) in accordance with procedures recognized as being adequate to detect any hazard to public health. Upon completion of the evaluation, a record shall be made of the handling of each deviation. Such records shall include, at a minimum, the appropriate processing and production records, a full description of the evaluation report and the disposition of the affected product. Such records shall be maintained in a separate file or log, and be made available to the inspector upon request.

    In the case of a stoppage of continuous agitating retorts, emergency scheduled processes may be established to permit compensation for temperature deviations, not to exceed 50°C (10°F). Such scheduled processes must be established in accordance with sub-section 15.4.4 of this document.

15.4.7 Cooling

To avoid thermophilic spoilage and/or organoleptic deterioration of the product, the containers shall be cooled as rapidly as possible to an internal temperature of about 40°C (105°F). In practice, water cooling is used for this purpose. Further cooling is done in air to evaporate the adhering water film. This aids in preventing both microbiological contamination and corrosion. If indicated, extra pressure can be applied during cooling to compensate for the internal pressure inside the container at the beginning of cooling, to prevent the deformation or leakage of containers. This can be minimized by equating the over pressure with the internal container pressure. When the integrity of the container is not adversely affected, water or air under atmospheric pressure may be used for cooling. Extra pressure is commonly achieved by introducing water or compressed air into the retort under pressure. The container and closure manufacturers' instructions shall be followed. To reduce thermal shock to glass containers the temperature of the cooling medium in the retort shall be reduced slowly during the initial cooling phase.

Air cooling alone may be used for products in which thermophilic spoilage is not a problem.

15.4.7.1 Cooling Water Quality

Although containers may normally be considered hermetically sealed, a small number of containers may leak during the cooling period mainly due to mechanical stress and pressure differential. Cooling water shall consistently be of low microbial content. (For example, an aerobic mesophyllic total colony count of less than 500 colony forming units (c.f.u.)/ml). Records shall be kept to demonstrate that cooling water is of acceptable microbiological quality (see 3.4.2. for frequency of tests and standards).

Water satisfying standards found in 3.4.2. (Chapter 3) including total count may be used as cooling in retorts with further treatment.

If water to be used for cooling does not meet with this microbiological specification, which is considered to be the case when cans are cooled in a cooling canal or when the cooling water is recirculated, then it must be treated in a manner which will ensure that at the time of use it will meet the specification. While chlorination is generally used as an effective treatment, other treatments such as ozone, iodine compounds, etc. may be used. An inspector that has serious doubts on the microbiological quality of the cooling water can request that samples be taken for microbiological analysis (coliform count, total plate count).

15.4.7.1.1 Chlorination Treatment

The chlorine must be thoroughly mixed with the water to a level sufficient to reduce the contamination to an acceptable limit. (A 20-minute contact time at suitable pH and temperature is normally considered adequate. Shorter contact times may be used under certain circumstances). The effect on the microbiological quality of the cooling water must be determined and found acceptable. All results must be recorded.

The adequacy of a suitable chlorination treatment may be established by:

  1. the presence of a measurable residual free chlorine in the water at the end of the contact time;
  2. detectable amounts of residual free chlorine in the water after it has been used for cooling containers. (Residual free chlorine content of 0.5 to 2 p.p.m. is usually considered adequate. Chlorine levels in excess of this may accelerate corrosion of certain metallic components); and
  3. a low microbial content of the water at the point of use.

Once a suitable system has been established, the adequacy of treatment is indicated by measuring and recording the free residual chlorine according to b) above. In addition, water temperature and pH shall be measured and recorded since marked changes from the reference values previously established may adversely affect the disinfecting action of the added chlorine.

The amount of chlorine required for adequate disinfection will depend upon the chlorine demand of the water, its pH and temperature. Where water with a high level of organic impurity, (e.g., surface water) is used as a source of supply, it will usually be necessary to provide suitable treatment for separation of impurities, prior to disinfection by chlorine thereby reducing excessive chlorine demand. Recirculated cooling water may gradually increase in organic load and it may be necessary to reduce this by separation or other means. If the pH of cooling water is greater than 7.0 or its temperature is above 30°C it may be necessary to increase the minimum contact time or concentration of chlorine to achieve adequate disinfection. Similar actions may be necessary with water disinfected by means other than addition of chlorine.

It is essential that cooling water storage tanks be constructed of impervious materials and protected by close fitting covers thus preventing contamination of the water by seepage, entry of surface water or other sources of contamination. These tanks shall also be fitted with baffles or other means of ensuring thorough mixing of water and chlorine or other disinfectant. They shall be of sufficient capacity to ensure that the minimum residence time is achieved. Particular attention shall be paid to positioning of inlet and outlet pipes to ensure all water follows a pre-determined flow pattern within the tank. Cooling tanks and systems shall be drained, cleaned and refilled periodically to prevent excessive organic and microbial build-up. Records shall be kept of such procedures.

Measurements of microbial content and chlorine or alternative disinfectant levels shall be made with sufficient frequency to enable adequate control of cooling water quality.

15.4.8 Post-process Container Handling

A small proportion of correctly made and closed cans may be subject to temporary leaks (micro leakage) during the later stages of cooling and for as long as the cans and their seams remain externally wet. The risk of micro leakage may be increased if poor seam quality and inadequately designed container conveyor, handling, labelling and packaging equipment result in increased can abuse. When such leakage occurs, water on the can provides a source and a transport medium for microbial contamination from conveyor and equipment surfaces to areas on or near the can seams. To control leaker infection it is necessary to ensure that:

  1. cans are dried as soon as possible after processing;
  2. conveying systems and equipment are designed to minimize abuse; and
  3. conveyor and equipment surfaces are effectively cleaned and disinfected.

Glass jars may be similarly affected.

The post-process area shall be effectively separated from raw food to avoid cross-contamination. Precautions (i.e. notices posted in critical areas) shall also be taken to ensure personnel from the raw food areas do not have uncontrolled access to the post-process area.

Generally, temporary leaks are not a problem with correctly formed heat seals on semi-rigid and flexible containers. However, leakage may occur through defective seals and perforations in the container bodies. Therefore the requirements for drying containers, minimizing abuse and ensuring effective cleaning and disinfection of conveyor systems are equally applicable to these types of containers.

15.4.8.1 Retort Crate Unloading

To minimize leaker infection, processed containers should not be manually handled while still wet.

Before unloading retort crates, water shall be drained from container surfaces. In many instances this can be accomplished by tilting the retort crates as far as possible and allowing sufficient time for the water to drain. The containers shall remain in the crates until dry before unloading by hand. Unloading of wet containers by hand presents a risk of contamination from food poisoning organisms which may be transferred from the hands onto the container.

15.4.8.2 Container Drying

Where used, driers shall be shown not to cause damage to or contaminate containers and shall be readily accessible for routine cleaning and disinfection. Not all driers meet these requirements. The drying unit shall be employed in the line as soon as practicable after cooling.

Labelling and packaging operations are to be considered only after the containers are dry.

Driers do not remove all cooling water residues from container external surfaces but they reduce significantly the time containers are wet. This reduces the length of post-drier conveying equipment that becomes wet during production periods and which requires extra cleaning and disinfection measures.

The drying of batch processed containers may be accelerated by dipping the filled retort crates in a tank of a suitable wetting agent. After immersion (15 seconds) the crates should be tipped and allowed to drain. It is essential that the solution of wetting agent be kept at not less than 80°C to avoid microbial infection and be changed at the end of each shift.

15.4.8.3 Container Abuse

Mechanical shock or abuse is mainly caused by either containers knocking into each other, (for example, on gravity runways), or by pressing against each other, (for example, when the backup of containers on cable runways results in the development of excessive pressure). Abuse may also be caused by containers hitting protruding sections on conveying systems. Such mechanical shocks may cause temporary or permanent leaks and result in infection if the containers are wet.

Careful attention to the design, layout, operations and maintenance of conveying systems is necessary if abuse is to be reduced to a minimum. (One of the commonest design faults is unnecessary changes in the height of different sections of the conveying system. For line speeds above 300 cpm, (containers per minute), multi-lane conveying systems coupled with container accumulation tables are recommended. Sensors should be installed to allow the conveyor to be stopped if excessive build up of containers occur.) Poor seam quality in combination with inadequately designed, adjusted or maintained unscrambling, labelling and packaging equipment increases the risk of micro leakage. Special care shall be taken to prevent abuse to glass containers and their closures, as well as to semi-rigid and flexible containers.

Abuse of semi-rigid and flexible containers may lead to perforation of the container or to flexcracking in the case of pouches. Therefore these types of containers should not be allowed to fall or slide from one section to another of the conveying system.

15.4.8.4 Post-process Cleaning and Disinfection

Any container conveyor or equipment surface that is wet during production periods will permit rapid growth of infecting microorganisms unless it is effectively cleaned at least once every 24 hours and, in addition, regularly disinfected during production periods. The chlorine in the cooling water deposited on these surfaces from cooled cans is not an adequate disinfectant. Any cleaning and disinfection program that is instituted shall be carefully evaluated to ensure that microbial loads are reduced to a minimum before being adopted as a routine procedure. The assessment of the continuing effectiveness of post-process cleaning and disinfection programs can only be established by bacteriological monitoring.

Conveying systems and equipment shall be critically examined with the view to replacing unsuitable materials. Porous materials shall not be used and surfaces which become porous, heavily corroded or damaged shall be repaired or replaced.

All personnel shall be made fully aware of the importance of personal hygiene and good habits in relation to post-process container handling.

Post-cooling areas of continuous cookers, including hydrostatic cookers, may constitute continuing sources of high bacterial concentrations unless stringent measures are taken to clean and disinfect them regularly to avoid microbial build up.

When containers are to be over wrapped, the secondary wrap shall be placed on dry containers only. Generally, flexible and semi-rigid containers should be over wrapped to protect from perforation or cracking during shipping and handling.

15.5 Quality Assurance

It is important that scheduled processes be properly established, correctly applied, sufficiently supervised and documented to provide positive assurance that the requirements have been met. These assurances apply also to the seaming and sealing operations. For practical and statistical reasons, an end-product analysis by itself is not sufficient to monitor the adequacy of the scheduled process.

15.5.1 Processing and Production Records

Permanent, legible and dated records of time, temperature, codes and other pertinent details shall be kept concerning each retort load or code lot for continuous retorts or aseptic processes. Such records are essential as a check on processing operations and will be invaluable if some question arises as to whether a particular lot had received adequate heat processing. These records shall be made by the retort or processing system operator or other designated person, on forms which shall include: product name and style, the code lot number, the retort or processing system and recorder chart identification, the container size and types, the approximate number of containers per code lot interval, the minimum initial temperature, the scheduled and actual processing time and temperature, the recorder-controller and indicating thermometer readings, and other appropriate processing data. Closing vacuum (in vacuum-packed products), fill-in weights, filled flexible pouch thickness, and/or other critical factors specified in the scheduled process shall also be recorded. When deviations occur in the application of the scheduled process refer to sub-section 4.6 of this Code. In addition, the following records shall be maintained:

15.5.1.1 Processing in Steam

15.5.1.1.1 Static Autoclaves
  • time steam on;
  • venting time and temperature;
  • time sterilization temperature reached; and
  • time steam off.
15.5.1.1.2 Batch Agitating Retorts

As for still retorts (see 15.5.1.2.1) with additions of functioning of condensate bleeder as well as retort and/or reel speed. Where specified in the scheduled process it is important to also record container head space and critical factors such as in-going product consistency and/or viscosity, maximum drained weight, minimum net weight and per cent solids (see 15.4.4.2).

15.5.1.1.3 Continuous Agitating Retorts (See 15.5.1.1.2)
15.5.1.1.4 Hydrostatic Retorts

The temperature in the steam chamber should be at just above the steam-water interface, at the top of the dome, if applicable, speed of the container conveyor, and, where the scheduled process specifies, measurements of particular temperatures and water levels in the hydrostatic water legs.

In addition, for agitating hydrostatic retorts, rotative chain speed, and other critical factors such as the head space and in-going product consistency.

15.5.1.2 Processing in Water

15.5.1.2.1 Static Autoclaves
  • time steam on;
  • come-up time;
  • time sterilization starts;
  • sterilization temperature;
  • water level;
  • water circulation and pressure maintained; and
  • time steam off.
15.5.1.2.2 Batch Agitating Retorts

As for still retorts (Sub-Section 15.5.1.2.1) with the addition of retort and/or reel speed. Where specified in the scheduled process it is important to record container head space and critical factors such as in-going product consistency, maximum drained weight, minimum net weight and per cent solids (see 15.4.4.2).

15.5.1.3 Processing in Steam/Air Mixtures

15.5.1.3.1 Static Autoclaves
  • time steam on;
  • come-up time;
  • time sterilization starts;
  • maintenance of circulation of steam/air mixture;
  • pressure;
  • sterilization temperature; and
  • time steam off.

15.5.1.4 Aseptic Processing and Packaging

Detailed automatic and manual record requirements depend on the type of aseptic processing and packaging system, but they must provide complete and accurate documentation of the pre-sterilization and running conditions actually used.

15.5.1.4.1 Product Container Sterilization Conditions

Record sterilization media flow rate and/or temperature, where applicable, retention time in the sterilizing equipment of containers and closures. Where a batch system is used for container and/or closure sterilization, sterilization cycle times and temperatures should be recorded.

15.5.1.4.2 Product Line Conditions (see 15.4.5.6)

Record pre-sterilization of the product line, "stand-by" and/or "change-to-product", as well as running conditions. Running condition records should include product temperature at the final heater outlet, product temperature at holding section outlet, differential pressures if a product-to-product regenerator is used, and the product flow rate.

15.5.1.5 Flame Sterilizers

  • container conveyor speed;
  • can surface temperature at the end of the process holding period; and
  • nature of container.

15.5.2 Record Review and Maintenance

15.5.2.1 Processing Records

Recorder charts shall be identified by date, product, container size, retort and where applicable the cooker shell number and other data as necessary volume of production, so they can be correlated with the written record of lots processed. Each entry on the record shall be made by the retort or processing system operator, or other designated person, at the time the specific retort or processing system condition or operation occurs, and the retort or processing system operator or such designated person shall sign or initial each record form. Prior to shipment or release for distribution, but not later than one working day after the actual process, a representative of plant management who is knowledgeable and experienced in canning technology shall review and ensure that all processing and production records are complete and that product received the scheduled process. The records, including the recorder thermometer chart, shall be signed or initialled by the person conducting the review.

15.5.2.2 Container Closure Records

Written records of all container closure examinations shall specify the code lot, the date and time of container closure inspections, the measurements obtained, and all corrective actions taken. Records shall be signed or initialled by the container closure inspector and shall be reviewed by a representative of plant management who is knowledgeable and experienced in canning technology with sufficient frequency to ensure that the records are complete and that the operation has been properly controlled.

15.5.2.3 Water Quality Records

Records shall be kept of the results of all tests of microbiological quality and cooling water treatment records shall be retained for at least three years.

15.5.3 Retention of Records

The records specified in Sub-Sections 15.4.4, 15.4.7, 15.5.1 and 15.5.2 shall be retained for a period of not less than three years to assist investigation of problems. They shall be held in a manner which will permit ready reference by the processor. The statement of a scheduled process shall be retained for at least three years after its discontinuation of its use.

15.6 Storage and Transport of Finished Product

Conditions of storage and transport shall be such that the integrity of the product container and the safety and quality of the product are not adversely affected. Attention is drawn to common forms of damage such as that caused by improper use of fork lift trucks.

Warm metal containers should not be stacked so as to form incubation conditions for the growth of thermophilic organisms.

High humidity storage should be avoided. Metallic containers kept at high humidity particularly for a long time and especially in the presence of mineral salts or substances which are even very weakly alkaline or acidic are likely to corrode.

Labels or label adhesives which are hygroscopic and therefore liable to promote rusting of tinplate should be avoided as should pastes and adhesives that contain acids or mineral salts.

Cases and cartons should be thoroughly dry. If they are made of wood it should be well seasoned. They should be of the proper size so that the containers fit snugly and are not subject to damage from movement within the case. They should be strong enough to withstand normal transportation.

Metal containers should be kept dry during storage and transportation. The mechanical properties of outer cartons etc. are adversely affected by moisture and the protection of the containers against transport damage may become insufficient.

The storage conditions, including temperature, should be such as to prevent deterioration or contamination of the product. Rapid temperature changes during storage should be avoided as this may cause the condensation of moist air on the containers and thus lead to container corrosion.

15.7 Laboratory Control Procedures

Each establishment should have access to laboratory facilities to assist in the control of the process and as well as the product packed. The amount and type of such control will vary with the food product as well as the needs of management. Such control should reject all food that is unfit for human consumption.

Where appropriate, representative samples of the production should be taken to assess the safety and quality of the product.

Laboratory procedures used should follow recognized or standard methods in order that the results may be readily interpreted.

Laboratories checking for microorganisms shall be well separated from food processing areas.

15.8 End Product Specification

Microbiological, chemical, physical or extraneous material specifications may be required depending on the nature of the food. Such specifications should include sampling procedures, analytical methodology and limits for acceptance.

To the extent possible under good manufacturing practice the products shall be free from objectionable matter.

The products shall be commercially sterile, and not contain any substances originating from microorganisms in amounts which may represent a hazard to health.

The products shall be free from chemical pollutants in amounts which may represent a hazard to health.

15.9 Incubation

Spoilage of canned goods is generally due to growth of microorganisms after heat processing, either from under processing, faulty cooling or post processing contamination via leakers.

Microbial growth within the can often, but not always, results in production of gas and a consequent loss of vacuum. If gas production continues flippers or blown cans result.

Note that growth of C. botulinum may occur without gas production. The incubation test alone cannot be relied for product safety or replace close control of each processing step; however, incubation of cans after processing provides a simple means to routinely check for processing defects.

It is the duty of the inspection staff to monitor the incubation procedure and to ensure that it is done as described in this section.

15.9.1 Incubation Facilities

The establishment shall provide incubation facilities which include a thermometer, a temperature/time recording device, a means for the circulation of the air inside the incubator to prevent temperature variations, and a means to prevent unauthorized entry into the facility. An employee designated by the operator shall be responsible for the security of the incubator.

15.9.2 Product Requiring Incubation

Shelf stable product requiring incubation includes:

  1. low acid products; and
  2. acidified low acid products.

15.9.3 Incubation Samples

  1. From each load of product processed in a batch type thermal processing system (still or agitation) the operator shall select at least one container per retort basket for incubation.
  2. For continuous rotary retorts, hydrostatic retorts, or other continuous type thermal processing systems, the operator shall select at least one container per 1000 for incubation.
  3. Only normal-appearing containers shall be selected for incubation.
  4. The operator shall identify the selected containers to ensure they are incubated for the required period of time.

15.9.4 Incubation Temperature and Time

The required samples for shelf stable products shall be tested by incubation for at least 10 days at 37 ± 1°C.

15.9.5 Incubation Checks and Records Maintenance

A designated person shall visually check all containers under incubation each working day and the inspector shall be notified when abnormal containers are detected. For each incubation test the establishment shall record at least the product name, container size, container code, number of containers incubated, in and out dates, and incubation results. The establishment shall retain such records, along with copies of the temperature/time recording charts for at least three years.

15.9.6 Abnormal Containers

The finding of abnormal containers among incubation samples is cause to officially retain at least the code lot involved.

Note: When abnormal containers are detected by any means other than incubation, the operator shall inform the inspector and the affected lot(s) shall not be shipped until the inspector is satisfied that the product is safe and fit for human consumption.

15.9.7 Shipping

In those instances where a good record of proper canning procedures has been demonstrated and routine incubation tests have proven negative, the operator may be permitted to ship product to another registered establishment or to a distribution warehouse for storage, without awaiting the results of the incubation tests for the particular lot, provided that the inspector is advised of the product destination, and the product is not offered for sale until the results are known.

Where product leaves the originating establishment prior to incubation being complete, the operator must maintain a detailed record of product codes, amount shipped and destinations, in case a recall is initiated.

15.10 Records to Maintain

15.10.1 Processing and Production Records

  1. Processing and production information should be entered by the retort or processing system operator or other designated person, on forms which should include the product, the code number, the retort or processing system number, the size of container, the approximate number of containers per coding interval, the minimum initial temperature, the actual processing time and temperature, the mercury-in-glass and recording thermometer readings, and other appropriate processing data. Closing machine vacuum (in vacuum-packed products), maximum drained weight, or other critical factors specified in the scheduled process should also be recorded. In addition, the following records should be maintained:
    1. Still retorts

      Time steam on: time temperature up to processing temperature; time steam off; venting time and/or temperature to which vented (as applicable).

    2. Agitating retorts

      Functioning of condensate bleeder; retort speed; and, where specified in the scheduled process, head space, consistency, maximum drained weight, minimum net weight and percent solids.

    3. Hydrostatic retorts

      The temperature in the steam chamber between the steam-water interface and the lowest container position; speed of the container conveyor chain: and where the scheduled process specifies maintenance of particular temperatures in the hydrostatic water legs, the temperatures near the top and the bottom of each hydrostatic water leg.

  2. Recording thermometer charts shall be identified by date, and other data as necessary, so that they can be correlated with the written record of lots processed, Each entry on the record shall be made by the retort or processing system operator, or other designated person, at the time the specific retort or processing system condition or operation occurs, and the retort or processing system operator or such designated person shall sign or initial each record form. Not later than one working day after the actual process, and prior to shipment or release for distribution, a representative of plant management who is qualified by suitable training or experience shall review all processing and production records for completeness and to ensure that the product received the scheduled process. The records, including the recording thermometer chart(s), shall be signed by the individual conducting the review.
  3. Written records of all container closure examinations should specify the product code, the date and time of container closure inspections, the measurements obtained, and all corrective actions taken. Records should be signed by the container closure inspector and should be reviewed by management with sufficient frequency to assure that the containers are hermetically sealed.
  4. Written records should be kept to show that desired equilibrium pH is obtained where the food acidity is adjusted for processing.
  5. Records shall be kept on cooling water chlorination and microbiological testing.

15.10.2 Distribution Records

Records shall be maintained identifying the initial distribution of the finished product.

Copies of all records provided for in this section except those on cooling water chlorination, shall be kept by the company for a period of not less than three years, and shall be available to an inspector at any time.

15.10.3 Incubation Records

A permanent log shall be maintained by an inspector, listing product, code, number of containers, dates of start and finish of incubations period, together with results of all examinations (cans should be examined at least every three days).

15.11 Required Inspection Procedures (Additional to normal monitoring of construction, sanitation, etc.)

15.11.1 Verification of Empty Container Inspection

  • check plant quality control records;
  • monitor testing procedures;
  • visually inspect sample of empty containers before filling point, for defects and cleanliness; and
  • check equipment used to clean cans for proper functioning

15.11.2 Verification of Handling and Storage of Incoming Product, Product Preparation, Filling and Closure Operations

  • check plant quality control record;
  • monitor testing procedures;
  • check coding on cans;
  • check external surfaces for cleanliness, require washing if necessary;
  • check for heat sensitive identifiers; and
  • visually inspect sample of closed containers;

15.11.3 Verification of Retort Operations

  • check plant quality control records;
  • ensure that thermal processes are posted and accessible to retort operators and monitor thermal processing;
  • check for correlation between thermometers; and
  • check for heat sensitive identifiers.

15.11.4 Verification of Cooling Operations and Post Retort Handling

  • check water testing and satisfactory chlorine levels; and
  • visually inspect cooled containers for defects.

15.11.5 Controlling Incubation Procedures

  • ensure an adequate number of samples is identified and placed in incubator;
  • examine samples daily during incubation period;
  • record date in and date out of each sample along with all relevant information; and
  • monitor temperature charts.

15.11.6 Verification of Distribution Records

  • Ensure that destination, etc. of all lots, especially those released prior to completion of incubation is properly recorded.

15.12 Lot Sampling and Inspection Procedures

In those cases where a lot of meat product packed in hermetically sealed containers (canned foods) is to be sampled and inspected, the procedure to be followed is described in Chapter 10 of this manual.

15.13 Recall Procedure

The operator shall prepare and maintain a current procedure for the recall of all canned products covered by this chapter. Upon request, the recall procedure shall be made available to the inspector for review.

15.14 Guidelines for Temperature Studies When Processing in Steam Still Retorts Exclucing Crateless Retorts

15.14.1 Introduction

Only persons experienced and knowledgeable on thermal processing in steam still retorts should carry out and evaluate the results of such studies.

15.14.2 Application

Temperature distribution studies should be done to: develop or validate a venting schedule; to locate cold or slow heating zones in preparation for heat penetration studies; in the case of new installations; and for any changes to an installation which may influence the temperature distribution in the product zone. Examples are: changes to steam spreaders, decreased steam pressure in lines, changes to the product loading patterns, changes to the basket and/or dividers, etc.

15.14.3 Inventory of the Thermal Processing System

Prior to the selection of the test retort(s) a survey should be made of the following:

15.14.3.1 Lay-out Diagram

A detailed diagram identifying all equipment for which the use of steam is required (including the numbering system used to identify each retort) and the steam supply line arrangement should be made as prescribed in this section. (Note that it is recommended that all steam lines from the main line to the retort(s) be clearly identified in the diagram from those steam lines feeding other equipment).

15.14.3.2 Steam Supply to the Retorts

15.14.3.2.1 Boiler(s) Capacity (psi or kPa)

Record potential and actual settings, amount of steam developed and available i.e. pounds or kilograms of steam produced per unit time.

15.14.3.2.2 Retort Header Pressure

It is important to insure that adequate steam pressure and volume is being delivered to the retort(s). This measurement should be taken when maximum operational demands are made on the steam supply.

15.14.3.2.3 Headers, Manifolds, Lines and Valves

Record pipe size and length, valve size and types, of the main steam line from the boiler(s) immediately before the pressure/steam regulator to the retort(s).

15.14.3.2.4 All Connecting Steam Lines Other Than to the Retort

Record size of all connecting steam lines to the main steam line noting other equipment using steam (e.g. blanchers, exhaust boxes, etc.)

15.14.3.3 Retort(s)

A detailed diagram of each retort including associated operational equipment as identified below should be made. Where identical retort configurations exist, one diagram is sufficient. The designated retort number(s) must be shown on the diagram.

15.14.3.3.1 Retort Shell

Record retort type and internal dimensions. For vertical retorts, note the presence of centering guides and/or baffle plates.

15.14.3.3.2 Retort Crates

Record maximum number of crates used in each run as well as their design and dimensions.

15.14.3.3.3 Steam Supply From Pressure/Steam Regulator to Retort

Record pipe sizes, valve type and sizes, pressure/steam regulators or reducers and all pipe fittings including steam by-pass lines and steam spreaders (shape, pipe size, length, location; number, size and location of holes in pipe).

15.14.3.3.4 Steam Control

Record type of controller (i.e. pressure to air, temperature to air) and location of sensor.

15.14.3.3.5 Air System for Controls (if applicable)

Record size of air compressors, air dryer capacity, filter type and location(s). Include the line pressure that must be maintained for operation of the controls and how this pressure is controlled.

15.14.3.3.6 Other Piping and Required Equipment

Record the following information:

  1. Vents: location, length and size of pipes, also type and size of valves.
  2. Vent manifold or manifold headers: location, length and size of all pipes, connecting pipes, and valve(s) type(s) and size, where applicable.
  3. Bleeders, mufflers: location, number, size and construction.
  4. Drains: location and size. In addition, note where they drain and whether they are open to the atmosphere.
  5. Water supply (if applicable): location and size of pipes, valve type and size.
  6. Air supply (if applicable): location and size of pipes, valve type and size, and the available air pressure.
  7. Temperature indicating device (Mercury-in-glass thermometer or equivalent): location of the sensing point in the retort and date/year when it was last calibrated.
  8. Temperature controller: sensing point location in the retort.
  9. Pressure gauge: location of the sensing point in the retort and date/year it was last calibrated.
  10. Additional piping or equipment such as condensate removal systems, etc.
15.14.3.3.7 Recording Device

Note type of recording device (recorder or recorder/controller). For more information, consult section 7.6.2.2 of the Recommended Canadian Code of Hygienic Practice for Low-acid and Acidified Low-acid Foods in Hermetically Sealed Containers (Canned Foods).

15.14.3.4 Loading Equipment

Record the following information:

  1. Container size, loading configuration and maximum number of containers per layer or per basket (scramble pack).
  2. Maximum number of baskets in each retort.
  3. Hole size and spacing of the basket base plate.
  4. Determine the percent open area of the base plate and separator sheets if used in the crates or baskets. Where separator sheets are located over a base plate they should be positioned to reflect the worst case scenario.

Note: It is important to correctly document the survey findings in order to enable a proper evaluation before selecting the test retort(s). The documented survey should be maintained on company's file and updated when necessary.

15.14.3.5 Selection of Test Retort(s)

All information required in section 15.14.3 above must be taken into consideration when selecting the test retort(s). The retort(s) selected should represent the worst possible condition that could influence the delivery of the venting procedure. Note that under certain conditions (i.e. when the plumbing and equipment configuration is not identical for all retorts), it may be necessary to carry out a temperature distribution study of a number of retorts in a system in order to determine which one represents the worst case.

Where all plumbing and equipment configuration is identical, it is generally advisable to select as the worst possible case the retort which is located at the end of the steam line. However, this is not always the case. This is an area where the knowledge and experience of the specialist supervising the studies is of utmost importance.

15.14.4 Test Equipment

15.14.4.1 Data Logger

Note if the data logger has a sufficient number of channels to adequately monitor and record temperatures during the temperature distribution study.

15.14.4.2 Thermocouples

Note if the thermocouples and lead wires, or other temperature measuring devices used are of an appropriate type, size, length, and number to adequately monitor the temperatures within the retort.

15.14.4.3 Temperature Indicating Device

Note which type is used (Mercury-in-glass thermometer or other) see 15.14.3.3.6 item 8.

15.14.4.4 Pressure Indicating Device(s)

Note which type is used (if required) see 15.14.3.3.6 item 9.

15.14.4.5 Stuffing Box (packing gland)

Note if the diameter is sufficient to accommodate number of lead wires (if thermocouples are used as the temperature measuring device) and specify its location on the retort.

15.14.5 Standardization of Test Equipment

15.14.5.1 Retort Mercury-in-glass (MIG) Thermometer (or equivalent temperature indicating device)

Prior to performing a temperature distribution test the MIG thermometer (or equivalent) shall be certified by a recognized authority as meeting the stated accuracy.

15.14.5.2 Temperature Measurement System (e.g. data logger, thermocouples, extension wires, or other Temperature Measuring Devices (TMD) etc.)

  1. Prior to conducting a temperature distribution test, standardization of test equipment (see section 4) must be performed using the test retort selected. All leads, extensions and connections should be assembled as they will be used under actual operational conditions.
  2. Place one or more TMDs in close proximity of the known accurate retort Mercury-in-glass thermometer probe (or equivalent). Care should be taken not to inhibit steam flow past the thermometer probe (or equivalent).
  3. The retort is brought up to the temperature to be used during the temperature distribution tests and the entire system is allowed to run for ten minutes after equilibrium is reached.
  4. All TMDs should be standardized at the intended retort operational temperature. Thus, a variance among the TMDs to be used can be identified and those which vary by more than 0.3°C (0.5°F) from the standard thermometer should be discarded. The range of all thermometers should be no more than 0.6°C (1°F). After correction factors have been incorporated, all TMDs should give the same reading.
  5. In order to meet the above calibration criteria, consideration must be given to minimizing errors due to variables inherent in any component of the temperature measuring system. For example, the use of thermocouple wire from the same spool is recommended to make all thermocouple leads and extensions.

15.14.6 Placement of the Temperature Measuring Devices in the Retort

A minimum of 12 TMDs (or equivalent) should be used. However, the number of TMDs depends upon many factors, for example, size of the retort chamber zone, container size, number and configuration in the baskets, etc. TMDs shall be placed in the following locations in the retort vessel:

  1. In close proximity to the Mercury-in-glass thermometer probe (or equivalent).
  2. In close proximity to the temperature controller probe. If this probe is in close proximity to the thermometer probe, this location is not necessary.
  3. Guidance as to the placement of TMDs in the product zone can be obtained from the design of the retort and the steam supply and distribution system as well as the loading pattern in the baskets or crates. However, location of cold zones does not always follow logic, specially when determining a venting schedule which requires freedom from steam/air pockets. This is an area where the knowledge and experience of the specialist supervising the study is of utmost importance.

    As a general guidance, it is recommended to place TMDs in the following manner:

    3a. For verticalFootnote 1 retorts:

    Temperatures should be measured in the middle of each basket at the top, centre and bottom. If more thermocouples are available, points along the edge at the top and bottom of each basket may be measured. If still more thermocouples are available, other points around the periphery of the basket may be measured.

    3b. For horizontalFootnote 2 retorts:

    In this type of retort, the product is usually in cars. In a horizontal retort thermocouples should be located in the middle of the basket at the top, centre and bottom of each car. If more thermocouples are available, they should be located at the centre of the outside of the four sides of the car.

    Note: A schematic diagram of the placement of all TMD(s) within the retort and covering all three dimensions should become part of information recorded for the temperature distribution tests.

  4. For determining the initial temperature (IT), TMDs should be placed in a sufficient number of testing medium filled containers. Generally, two containers have been found to be acceptable. Alternatively, a hand held thermometer that was previously calibrated may also be used to make that determination. Ideally, all containers in the retort should be equilibrated to a previously identified IT.

15.14.7 Preparing the Test Crates or Baskets With Containers

  1. Select the container size processed in the retorts, usually the smallest, that will yield the "worst" case situation for the operation.
  2. The product that has the highest heat absorption rate (convection heating) processed in the retorts should be used. Water may be used in the cans in place of product.
  3. Containers are placed in the crates or baskets in a manner that is equivalent to the worst case situation under the commercial operation. If separator or divider sheets are used between the layers of containers the sheets having the smallest percent total open area shall be used for testing.

15.14.8 Temperature Distribution Test

15.14.8.1 Set-up

  1. Review the retort survey
  2. Internal Temperature (IT)

The IT is usually determined from the container having the lowest temperature. When determining the test IT the range of initial temperatures to be encountered during normal commercial operation should be taken into account and the coldest IT be selected.

15.14.8.2 Critical Items

The following are critical and should be monitored and recorded during the test:

  1. controller temperature set points;
  2. internal temperature (IT);
  3. retort steam header pressure;
  4. time steam or time "0";
  5. time when the drain is closed, if it is open during a portion of the vent;
  6. time that vent is closed, retort temperature at the time the vent is closed as determined by the reference temperature measuring device;
  7. time when the reference temperature measuring device reaches the processing temperature;
  8. time when the controller (if applicable), advances to the "cook" cycle in the program or when the cook begins; and
  9. reference temperature measuring device readings - at sufficient intervals including the time it reaches the processing temperature.

15.14.8.3 Important Items

In addition, the following points are important and are highly recommended to be monitored and recorded during the test.

  1. time when the temperature recording device reaches the processing temperature set point; and
  2. retort pressure gauge (optimal) - readings - at sufficient intervals.

15.14.8.4 Conducting the Test

  1. The data logger should record the temperature of each temperature measuring device just prior to "steam on" and at sufficient intervals - not to exceed on minute - throughout the test. The data logger record shall become part of the test records.
  2. Critical items (see 15.14.8.2) should be recorded, as required, at intervals of sufficient frequency to describe and verify retort operating parameters during the test. These records shall become part of the test records and shall include the temperature recording chart(s).
  3. The test should extend for at least ten minutes after the retort control systems has stabilized and a definite temperature profile has been established for all TMDs.

15.14.8.5 Required Parameters for the Determination of a Vent Schedule

  1. On the basis of the data accumulated during the performance of temperature distribution testing on steam still retorts, excluding crateless retorts, a vent schedule should specify as a minimum the following critical parameters:
    1. vent time ("Steam on" to vent closed);
    2. vent temperature (when the vent valve is closed);
    3. where appropriate, minimum IT;
    4. use of any opening in the retort (other than the vent valve) during the vent period to increase vent capacity; and
    5. time and temperature when the drain is closed if it is opened during a portion of the vent.
  2. For a vent schedule to be determined successfully, it should be based on a minimum of three repeatable runs, and conducted under "worst case" conditions. "Repeatable" means that all three runs, conducted under the same test conditions, must show that adequate temperature distribution is achieved.
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