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Guide to Inspections of Low Acid Canned Food Manufacturers - 2 | 21 |
Valves may be operated by hand, pneumatically (by air, steam or other gas), electrically (by a solenoid or motor) or by a combination of these methods. Free flow valves such as the gate or ball valve are normally used on steam retort vent lines. The use of globe or other type valves on steam retort vent lines is not prohibited by the lacf regulations. If these types of valves are used, temperature distribution studies are required to document adequate temperature distribution in the retort prior to the start of the thermal process. Valves which provide a tight seal, such as the globe or ball valve must be used on air and water lines to prevent leakage into the retort during thermal processing. Valve seats and seals must be maintained to prevent the valves from leaking. During a lacf inspection the retort should be examined for evidence of leaking water and air valves. Some firms may employ the use of double valves on air and water lines to insure that no air or water is leaked into the retort during processing. TEMPERATURE DISTRIBUTION Temperature distribution is the work performed to ensure that the retort instrumentation accurately reflects that adequate temperature distribution has been achieved throughout the retort at the time that the sterilization cycle begins. This is accomplished by distributing an adequate number of thermocouples or other temperature measuring devices (TMDs) throughout the load (external to the containers), and making several runs or tests to ensure that temperature differences have been minimized. The number of thermocouples (TMDs) to be used is normally limited by the equipment available. A minimum of 12 thermocouples has been suggested by The Institute for Thermal Processing Specialists. With large retort systems and numerous retort crates a greater number of thermocouples may allow for a more extensive test to be completed. At least one thermocouple is placed next to the MIG thermometer and used as a reference during the study. The worst case situation for temperature distribution normally occurs when heat flow to the product is the greatest. The heat absorption rate of a convection heating (heat currents are formed in the container) is much higher than a conduction heating (heat must penetrate through the material) product. It is normally suggested that a convection heating product in the smallest container processed or a special cold water pack be used to test temperature distribution in still retorts. Other conditions may present the worst case for temperature distribution in a specific retort system or for a specific product or container type. This must be documented in the temperature distribution study. In some retort systems temperature distribution tests must be |