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Guide to Inspections of Low Acid Canned Food 27

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retort.

  1. The temperature of the retort must be controlled independently of the pressure.
  2. The containers are processed and cooled under water.

The water level in the retort must be maintained to provide water above the top level of the containers at all times. It is recommended that the containers be covered by at least 6 inches of water. If the water level falls below the level of the top containers those containers exposed to the steam/air mixture in the top of the retort must be identified and set aside for reprocessing or evaluation by a processing authority. A water level indicator is required on all water immersion retorts. This can be in the form of a water glass sight tube, pet cocks, or mechanical indicator. A low-water alarm (visual & audible) is suggested. The operator must observe the water level during processing to insure that the water does not drop below the level of the top containers. At a minimum observations should be made and recorded at the start of the process and at the end of the thermal process prior to the addition of cooling water to the retort. A non-clogging water tight drain valve is required to prevent leakage of water from the retort during processing. It is suggested this valve be screened to protect the valve from being clogged with broken glass and other debris.

Heating and circulation of the water to provide for uniform thermal processing temperatures in the retort system is important.

Steam introduction into the bottom of vertical retorts can be accomplished in one of several satisfactory ways. One way is by using a steam spreader equipped with six pipes radiating out from the center with "fish tail" nozzles which direct the flow of steam up along the sides of the vertical retort outside of the crates. A second acceptable method is to use a 4 legged cross steam spreader in which each pipe is perforated with holes directed 15° below horizontal along one side only. The legs are arranged in opposing pairs so that the holes face each other to give alternate live and dead quadrants. This arrangement provides for circulation of the water. In horizontal retorts the steam distributor should run the full length of the retort with perforations distributed uniformly along the pipe. Several still water immersion retorts of european design inject steam directly into the water circulation line to maintain the processing temperature. Any of the above, or other methods, are appropriate as long as there is documentation in the form of temperature distribution data or other documentation from a processing authority that supports the method of heating the water.

Circulation of the water is important to provide uniform temperature throughout the retort. Adequate circulation of the processing water by air or pump must be established through procedures recognized by a processing authority per 21 CFR 113.40(b)(10)(i).

Air is added to the steam supply line prior to the steam spreader in vertical retorts to aid in the mixing of the water. As the air is added with the steam it also prevents steam 'knock" or "chatter" (a loud bumping sound) in the retort which happens when live steam is introduced into water. The air and steam mix to form bubbles out of the steam distributor. As the bubble moves up through the water the heat from the steam is lost to the water. The air that remains reaches the top of the vertical retort to provide the air overpressure. Excess pressure is released through the pressure control valve. A large flow of air (15 to 18 cubic feet per minute) is needed during the initial heating and come-up phases of the retort. This may be provided through an air bypass line. When the retort processing temperature is reached the flow of air can normally be reduced to (4 to 5 CFM). Air flow is normally regulated by placing an orifice in the line which provides a certain air flow at a regulated pressure. The air flow to vertical retorts should be documented during establishment of the temperature distribution in the retort. The air flow should be verified by the plant using a flow meter at intervals sufficient to insure that the retort is operating under the parameters used to establish the temperature distribution in the retort.

For horizontal retorts a water circulation system is recommended. This system uses a pump to draw water out of the bottom of the retort through several screened openings (suction manifold) and to discharge the water over the entire length of the top of the retort through a water spreader. The pump should be capable of circulating the entire volume of retort water at least every 4 to 5 minutes. A pilot light is normally used to indicate that the pump motor is running. Even though the light indicates that the pump motor is running this does not insure that the water circulation is adequate. Plugged lines, bent impellers on the pump and other mechanical problems may not be indicated. A flow meter on the circulation line is recommended to provide a true indication of water flow in the circulation line. Air must still be added to the horizontal retort to provide for the overpressure during processing.

Vertical still water immersion retorts are required to have centering guides, which should be installed so as to insure that there is a clearance of approximately 1 1/2" along the side of the retort to

 

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