Processing controls: Formulation and processing controls for processed cheeses, sweetened condensed milk and aerosol-packaged dairy products
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Introduction
This document provides recommended formulation and processing controls for:
- Processed cheeses produced with the aid of heat
- Cold-pack cheeses produced without the aid of heat
- Sweetened condensed milk
- Aerosol-packaged products
1. Processed cheeses
Processed cheese products with pH above 4.6 and water activity above 0.85 in hermetically sealed containers are considered as low-acid foods. They need to be commercially sterile (microbiologically stable) if kept at ambient. If the processed cheese product is not commercially sterile it requires refrigeration (4°C or below) and appropriate labelling.
Two criteria affect the safety of processed cheeses: heat treatment and formulation control. The heat treatment liquefies the product and destroys vegetative cells but not the viable spore-forming bacteria (may be pathogenic) of genus Clostridia and Bacillus. These spore-forming bacteria can cause defects in processed cheese by producing gas with or without off-odours. Proper product formulation will create a difficult environment for spore-forming bacteria to germinate and therefore produce a commercially sterile product.
Product analysis
Processed cheeses are characterized essentially by composition, water content and consistency. The three main groups are processed cheese, processed cheese food and processed cheese spread.
Processed cheese is a blend of fresh and natural aged cheeses which have been shredded and mixed. Emulsifying agents such as disodium phosphate or sodium citrate are added and the blend is heated, packaged and cooled, after which no further ripening occurs. The blend may consist of one or two or more varieties of natural cheese and may contain pimentos, fruits, vegetables, or meats. Smoked cheese or smoked flavour may also be added. A typical composition is 50.5% milk-fat-in-solids and 39.5% moisture. Processed cheese food is prepared similarly, except that it contains less cheese, with nonfat dry milk, or whey solids and water added. This results in a lower milk fat content and more moisture than in processed cheese. Processed cheese food contains not more than 46% moisture and not less than 23% milk fat. Processed cheese spread contains even more moisture (but not more than 60%) and the milk fat content is usually lower (but not less than 20%). A stabilizer such as carob bean gum or sodium alginate is used in the preparation of this product to prevent separation of ingredients.
Product formulation (includes processed cheese, processed cheese food and processed cheese spread)
- Control the following factors to prevent the germination of spore-forming bacteria after heat processing processed cheeses:
- Blend composition
- Sodium chloride concentration
- Type and concentration of emulsifying agent
- Water level
- pH
- Absence of natural inhibitors
- Prior treatment of condiments for example irradiation treatment, heat sterilization
- Use the following guidelines to keep processed cheese microbiologically safe after the heat treatment:
- Maintain a pH of 5.6 or lower (lower pH values increase safety)
- Maintain a moisture level of 60% or lower (the lower the moisture, the safer the product becomes)
- Maintain an emulsifier (sodium, potassium and calcium salts of the mono, di- and polyphosphoric acids; sodium, potassium and calcium salts of citric acid; citric acid and/or phosphoric acid with sodium hydrogen carbonate and/or calcium carbonate) concentration of up to 4% in total or up to 3.5% measured as anhydrous salts
- Maintain the moisture content and pH within the ranges indicated in Appendix F: Processed cheese microbiological stability chart for non-refrigerated products
- Maintain a water activity of 0.94 or less
- If new ingredients or changes in the processing conditions are introduced, conduct a new safety study
Microbial growth for both sporeformers and non-sporeformers should not occur in processed cheese. Any microbial growth (for example mesophilic non-sporeforming, mould) is evidence of lack of sterility and should be investigated.
Processing controls
Cookers are used in the manufacture of processed cheese. These cookers may be jacketed heated kettles or a continuous system consisting of a battery of stainless steel tubes.
For most processed cheeses the product's formulation and the cooking steps assure the safety and quality of the product.
- Ensure the heat processing step is well documented and well controlled
- For conventional recording charts, seal the unit to provide tamper evident restricted access to prevent adjustment by unauthorized personnel
- For computerized systems, protect the access to the computer to prevent adjustment by unauthorized personnel
- During the cooking process, validate the indicating thermometer temperature to the recording chart during and at the end of heating time as measured by the indicating thermometer
The recording chart information is part of the preventive control plan and provides the following information:
- plant name or licence number
- product name
- batch number
- corresponding indicating thermometer temperature during and at the end of heating time
- signature or initials of operator
2. Cold-pack cheeses
Product analysis
Cold-pack cheese or Club cheese is the blend of the same or two or more varieties of fresh and aged natural cheese, as in processed cheese, except that the cheese is mixed into a uniform product without heating. It may have a smoked flavour. The milk fat and moisture content depend on the variety or blend of cheese used.
Since cold-pack cheeses are not heat treated, nor do they contain bacteriostatic emulsifiers, they will contain viable microorganisms and therefore are not shelf stable.
Processing controls
In order to improve microbiological safety, take the following measures:
- Keep cold-pack cheeses refrigerated (4°C or below) and appropriately labelled
- Put in place a raw product quality control program
- Follow good manufacturing practices, for example clean equipment and environment, personnel hygiene and practices, etc.
3. Sweetened condensed milk
The manufacture of sweetened condensed milk is similar to that of evaporated milk. The milk is not sterilized and crystallization is controlled by cooling. The extended shelf life of sweetened condensed milk is derived not from thermal processing, but from the reduced water activity (Aw) level resulting from the high solute concentration (40 - 45% sugar). The Aw is sufficiently low to inhibit growth of many bacteria. Other micro-organisms, especially yeasts and moulds, are able to develop.
Product analysis
Sweetened condensed milk may be made from either whole or skim milk. The milk is preheated and, in some cases, superheated, before passing to the evaporator. Sugar (usually sucrose) or other sugars, may be dissolved in the preheated milk before evaporation or during the later stages of evaporation. The concentration of sugar in water is expressed as the sugar ratio (sucrose in aqueous phase) and may be calculated as:
sugar ratio = (% sugar in condensed milk × 100) ÷ (100 - total solids in condensed milk)
The sugar ratio is usually 63.5 - 64.5 for retail product, but can be as low as 42 for bulk, whole milk product to be stored under refrigeration. Sweetened condensed milk is not sterile and while the Aw level is sufficiently low to inhibit growth of many bacteria, other microorganisms are able to develop.
Product formulation
Sweetened condensed milk is subject to spoilage by osmotolerant yeasts, notably Torulopsis. The organism enters the milk after preheating, generally due to poor plant hygiene. The growth of the organism is slow, especially at lower ambient temperatures, but sufficient gas may be produced to swell the cans. Growth of moulds, usually species of Aspergillus and Penicillium, on the upper surface of the milk leads to the formation of “buttons”, small aggregates of mycelium and coagulated casein. The presence of mould is accompanied by off-flavours due to proteolysis. The reason for this is poor plant hygiene which can be further exaggerated by a large head space containing sufficient oxygen for excessive growth.
Most bacteria are unable to grow, but spoilage occasionally occurs, especially when there is a low sugar content. The relatively osmotolerant Micrococcus and Bacillus are most common. Typical spoilage patterns involve thickening, acid production, proteolysis, and in full cream products, lipolysis.
Processing controls
- Follow good manufacturing practices, for example clean equipment and environment, personnel hygiene and practices, etc.
- Due to the viscous nature of sweetened condensed milk, cleaning schedules may need to be adjusted accordingly
4. Aerosol-packaged products
Aerosol-packaged products such as whipped cream, are derived from cream that is ultra high temperature (UHT) processed, aseptically filled and pressurized by a propellant. Criteria that affect the safety of these products include heat treatment, formulation and manufacture control.
Product analysis
Stabilizers are a necessary component in the product formulation as well as the use of a propellant to pressurize the container. These propellants exist partly as a vapour in the headspace and partly as a liquid layer on top of the cream. Dispensing occurs at constant pressure but the contents are first shaken to form an emulsion. On release of pressure, cream is propelled through the outlet valve. The propellant volatilizes to form a whipped structure of high overrun; a specially shaped outlet nozzle permits the cream to be piped directly. The whip becomes less stable and shrinkage occurs on storage.
Product formulation
Cream based products have been associated with Listeria monocytogenes, Bacillus species and Staph aureus, due to in most cases post processing contamination, poor hygiene or inadequate heat treatment or failure in the packaging system.
Processing controls
In order to improve microbiological safety, take the following measures:
- Include controls for formulation, level of stabilizers and pressurization of the container
- End product testing (including chemical testing for correct fat content and microbiological testing) can be used to verify satisfactory processing and handling
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