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Dairy processing: Batch pasteurization systems

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Introduction

The following provides recommended practices for batch pasteurization of dairy products.

Batch (or vat) pasteurization is one of the first methods used to process milk. This system requires batch processing of small volumes of milk at a specific temperature for a long period of time. This method of pasteurization still exists in small plants to process fluid milk, and in larger plants to manufacture cultured products.

Record keeping

In a Preventive control plan (PCP), it is important to maintain and keep records of activities which demonstrate that the PCP is implemented and working effectively. Records can be in either a hard copy or electronic format. Refer to Record keeping for your preventive control plan for additional information.

Batch pasteurization records

Temperature and time requirements

Temperature and time are critical factors required to achieve pasteurization. Failure to achieve pasteurization could result in a microbiological hazard in the dairy product. The following are the generally accepted pasteurization schedules for dairy products produced by batch pasteurization.

Milk-based products containing below 10 % milk fat (fluid milk, goat milk, whey):

Milk-based products containing 10 % milk fat or higher, or added sugar (for example, fluid cream, cream for butter, chocolate milk, flavoured milk):

Frozen dairy product mixes and egg nog:

Other:

Process control records

The process control record is the legal record of the pasteurization process and therefore it is very important that it adequately and accurately reflect the heating process. Process control records also assist in tracking down quality and safety problems.

Verification of temperature and time

Process control records should substantiate that the minimum holding time is achieved by observing the batch pasteurization cycle.

Retention of process control records

Process control records substantiate that the products are adequately pasteurized.

Batch pasteurizer

Batch pasteurizers require specific design features and auxiliary equipment to ensure that every particle of milk is pasteurized. Milk is heated in the vat to the desired temperature by means of hot water either sprayed on the sides of the vat or circulated around the double jacket or by means of heating coils surrounding the inner jacket.

General conditions

A single- or 2-speed agitator, and a vertical baffle plate inside the vat are used to create efficient agitation for proper heat transfer. Effective agitation reduces the chance of burn-on on the inside wall.

Inlet/outlet valves and connections

Conditions for valves used on vat pasteurizers:

  1. Close-coupled vat outlet valve: the seat is either flush with the inner wall of the pasteurizer or so closely coupled that no milk or milk product in the valve is more than 0.5°C (1°F) colder than the milk or milk product at the centre of the pasteurizer at any time during the holding period.
    • A close-coupled valve, which is not truly flush, satisfies this condition when:
      • the vat outlet is flared so that the smallest diameter of the large end of the flare is not less than the diameter of the outlet line plus the depth of the flare, and
      • the greatest distance from the valve seat to the small end of the flare is no greater than the diameter of the outlet line, and
      • the outlet and the agitator are placed to ensure that milk current will be swept into the outlet
  2. Leak-protector vat outlet valve: has a leak-detecting device to prevent the contamination of pasteurized product surfaces including the valve outlet connection. When the valve is in any closed position, the device will prevent (redirect) leakage of milk or milk product past the valve.

Manual valves and the automatic valve system described below meet the above conditions.

For Air operated (Automatic) valve systems

Note: air operated (automatic) valve systems can be used to separate raw and pasteurized products on the outlet line of a vat pasteurizer, but not to separate raw and pasteurized product elsewhere in the system (see Appendix G: Preventing cross connections).

For plug-type outlet valves

Note: Butterfly valves do not meet the above criteria.

Additional criteria for valves and connections of a vat pasteurizer (see Appendix E: Diagram of valves):

Cover (ports)

Air space heating

Air space heating can be achieved by using an elevated pasteurization temperature or using an air space heater.

Indicating thermometer (batch pasteurization)

Indicating thermometers on batch pasteurizers provide the official processing temperature of the product.

General conditions

Batch indicating thermometers may be long stemmed and inserted directly into the product or inserted into a projectile well located in the side of the vat.

Types other than mercury actuated (for example, resistance temperature detectors (RTD)) may be used if they are of sufficient accuracy and precision. The criteria in Appendix J: Design criteria for digital thermometers for use in critical processes can be used to evaluate RTDs when used as alternatives to mercury actuated direct reading thermometers.

Specifications

Calibration

Indicating thermometer (air space)

An air space indicating thermometer ensures a temperature of at least 3°C (5°F) higher than the required minimum pasteurization temperature is maintained in the air space above the milk. This will guarantee that every particle of milk, including milk at the surface, will receive the full heat treatment.

General conditions

Types other than mercury actuated (for example, resistance temperature detectors (RTD)) may be used if they are of sufficient accuracy and precision. The criteria in Appendix J: Design criteria for digital thermometers for use in critical processes can be used to evaluate RTDs when used as alternatives to mercury actuated direct reading thermometers.

Specifications

Calibration

Recording thermometer (batch)

The recording thermometer automatically records the temperature of the product on a chart that also indicates the time of day, thus providing a record of the process and processing time.

General conditions

Recording pen

Sensor location

Chart specifications

Batch pasteurizers using temperatures above 72°C

Batch pasteurizers using temperatures below 72°C

Starter vats using temperatures above 80°C

Accuracy

Coil vats

A coil vat is a type of batch pasteurizer that may be used for pasteurizing cream for butter-making. A revolving heating coil gently agitates the cream to create uniform heating throughout the vat.

General conditions

Critical controls

Air space heating

Refer to Evaluation of dairy processing equipment for the general criteria for indicating and recording thermometers.

Records

The process control record is the legal record of the pasteurization process, so it is very important that it adequately and accurately reflects the heating process. Process control records also assist in tracking down quality and safety problems.

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