Guide to Inspections of Low Acid Canned Food 40
Manufacturers - 2
3. The fan is turned on to circulate the steam-air mixture. The retort is brought up to temperature during a 3-10 minute come-up period. The maximum amount of steam is injected at this time. The retort may use a steam bypass valve to provide a large flow of steam to the retort.
4. A process hold period during which the retort temperature is maintained at the correct temperature by the addition of steam through an automatic steam control valve. This may be a small steam supply valve used to maintain a more uniform temperature. Excess pressure is released through a small purge (vent) valve in the retort shell. Compressed air may be added to the rear of the retort to maintain the retort over-pressure.
5. Pre-cool, at the end of the thermal process a small amount of water may be injected into the retort steam-air channels to condense the steam or in some models cold water coils located in the retort are used to condense the steam.
6. Cooling is then completed by adding water to the retort through top or bottom water spreaders. In some of the newer systems plate heat exchangers may be used to cool products through indirect cooling.
The steam-air mixture is forced through the LaGarde retort by a fixed speed fan located at one end of the retort. The steam-air mixture is normally drawn through the basket by the fan (an automotive type blade fan in the LaGarde and a squirrel cage type in some other systems) and pushed back up along the sides of the retort through channels created by welding metal sheets to the top and bottom at each side of the retort. The plates are generally referred to as "directional baffles". The space between the plates and the retort shell is sometimes referred to as the steam-air "plenum". The flow rate is fixed at approximately 30 cubic feet per second.
LaGarde states that a temperature overshoot, (where the temperature of the retort is operated at several degrees above the required product temperature for the first part of the process and as the internal package temperature begins to achieve the desired temperature the temperature of the retort is reduced) can be used to produce a superior product. This process is reportedly designed to achieve shorter processing times and better heat transfer without stressing the container by causing high pressure within the containers. If the temperature overshoot is used it must be filed as part of the filed scheduled process.
The Lubeca LW3003 steam-air retort is offered in both static and rotational models. The Lubeca differs from the LaGarde in that in addition to using a large fan to mix the steam-air mixture this system also pumps the condensate from the bottom of the retort and distributes the condensate over the top of the containers. At the beginning of the process a small amount of water is added to the bottom of the retort. This water is heated by the addition of steam through steam spreaders in the bottom of the retort. A large squirrel type ventilator fan pulls air along the bottom of the retort and pushes the air along the top of the retort and back through the crates of product. Instrumentation is located in the shell of the retort. The temperature of the condensate and water may not be measured or recorded during production. Following the thermal process the containers are cooled by the addition of cooling water to the retort.
The Barriquand Steristeam retort differs from the LaGarde in that each basket has it own circulation fan. The fans are mounted on the side of the retort and circulate the steam-air mixture up over the basket and back through the containers. Cooling of product is normally through an external heat exchanger or by the addition of cooling water to the retort shell at the customers option.
The Truxton Steristar is a modified version of the LaGarde. The Steristar may use a squirrel cage or an automatic type fan, heavier components, proportional control valves, preheated compressed air and a number of other modifications to the LaGarde system. Operation of the system is similar to the LaGarde.
Air flow in the steam-air retort system is very important to the maintenance of proper temperature distribution during processing. Changes in the container, crate or loading configuration can change the air flow in the retort. Steam-air retorts are normally operated with a full load of product or with dummy crates of product to fill out the retort during the processing of partial loads. In some systems a baffle may be used to block off the retort at the last crate and allow for processing with less than a full retort load. Temperature distribution studies or other documentation should be on hand to demonstrate that adequate temperature distribution is achieved under less than full load conditions and with the container/crate configuration being used.
There should be some method for determining that the fan in a steam-air retort is operating. A visual inspection of the fan operation should be made on a routine basis. Inspection of operation of the fan should be documented.
Equipment and procedures for processing using flame sterilizers are covered by 21 CFR 113.40 (h). Flame sterilizers were employed initially, in part, in large size cans. for the processing of mushrooms