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Guide to Inspections of Low Acid Canned Food 26

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number of containers (depending upon can size) into the retort through the top sliding door. A counter counts the number of containers in the retort. The product containers fall into the water to limit container damage. The containers are jumble stacked in the retort. When the preset number of containers have entered the retort the containers are automatically diverted to the next retort to be filled. The hydraulic push button operated top sliding door of the retort is then closed. Steam is admitted to the retort through a spreader in the top of the retort, forcing out the cushion water which is normally collected, reheated, and reused. In some plants the cushion water is gravity drained before venting. The drain is left open until all cushion water has been removed from the retort and venting conditions met. Newer models of crateless retorts are normally equipped with a false bottom door at the exit end (bottom) of the retort. The false bottom door is perforated with holes which allow for a flow of steam between the false bottom door and the discharge door. The false bottom door also prevents containers of product from contacting the condensate which may build up in the bottom of the retort. Condensate is removed from the bottom of the retort through a condensate bleeder (normally 3/8" or larger) normally located in the bottom door of the retort. A 1/8" bleeder is recommended between the false bottom door and the condensate bleeder to provide visual assurance to the operator that there is no condensate buildup in the retort during thermal processing. Some older systems may still be encountered which do not use a false bottom and/or employ a second 1/8" bleeder. These systems should be carefully evaluated to determine that the condensate is being removed from the retort during thermal processing.

After the cushion water has been removed from the retort using the steam forced method, the retort is vented for a short period of time (this must be established by a processing authority). The processing of the product normally starts when the retort reaches processing temperature, but not before a free flow of steam is noted from the 1/8 bleeder located between the false bottom door and the discharge door. Failure of condensate bleeders to function properly in these retort systems has caused several instances of improperly processed lacfs. Condensate buildup in the bottom of the retort may contact only a few cans in the bottom of the retort, causing underprocessing of those containers. Such a situation can result in a very few cans of underprocessed product in a large lot of containers. After the product has been processed cooling water is normally brought into the retort to partially cool the product. In some systems the product is dumped from the bottom of the retort into a cooling canal. The discharge door on some systems is below the level of the water in the cooling canal. This causes a vacuum to be formed in the retort and the cans are supposed to drift slowly out of the retort into the cooling canal. A chain in the cooling canal then moves the container through the cooling water to the unscrambling station. In some of the older crateless retort systems containers were dropped into the cooling canal through a vibrating basket on the retort or directly onto a chain conveyor. Excessive container damage was sometimes noted in those systems.


Equipment and procedures for pressure processing in water in still retorts are covered by 21 CFR 113.40(b) of the lacf regulations. The requirements for still water immersion retort systems (Attachment 6) would also apply to those agitating systems used in the still non-agitating mode.

Thermal processing of glass, plastic, laminated pouch, and large profile metal containers require that an over pressure greater than the pressure created by the retort temperature be provided to maintain container integrity. Pressures in the range of 20 to 32 psig are normally used for glass containers. As the product in a container is heated to high temperatures, pressures exceeding those of the retort can be created in the container. This higher pressure is due to the combination of increased vapor pressure and expansion of the contents in the container. In the case of small metal cans, the metal can may be able to withstand these pressures without permanent distortion of the metal in the can. In the case of glass jars and other less durable containers, an over-pressure must be used to prevent the container from venting the contents, or becoming permanently distorted or destroyed. The water immersion still retort was first designed for use in processing glass jars. Water immersion still retorts are now used to process a variety of containers requiring an over-pressure. In some cases the water immersion retort may be used to process small metal containers as well. If the water immersion retort is used to process metal containers there is some concern with the rusting of containers caused by the addition of air to the processing water.

Basically there are four principle differences in a still retort equipped for pressure processing in water as compared to a still steam retort:

  1. Compressed air must be provided to the retort to create the overpressure during processing and cooling.
  2. A pressure control valve must be added to the

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