Guide to Inspections of Low Acid Canned Food 36
Manufacturers - 2
dividing the desired process time into the number of carriers in steam.
Number of carriers in steam = Carriers-per-minute
Process time in minutes
- Calculate the actual carriers-per-minute rate by timing 50 carriers with a stop watch. Divide this time in seconds into 3,000 to get actual carriers per minute.
3,000 = Carriers-per-minute
Seconds for 50 carriers
CASCADING WATER RETORTS
Equipment and procedures for processing in cascading water retorts are not specifically covered in the lacf regulations. These systems are covered by 21CFR 113.40(j), Other Systems. Other systems are required to conform to the applicable requirements of the lacf regulations.
Cascading water retorts are known to be manufactured by the Food Processing Machinery Division of FMC U.S.A. (Universal and Convenience sterilizers), Lubeca in Germany (Lubeca Model LW406 and LW402 G), Herman Stock in Germany (Autovap and Rotovap), Phoenix A/S a division of the Klinge Corporation in Denmark (Phoenix) and by Barriquand in France (Steriflow). Copies of these retort systems may be made in other countries. Custom built cascading water systems may also be encountered.
Cascading water retorts may be either still or end over end agitating batch type retorts. They are normally operated with an air over-pressure and may be used to process a wide variety of container types including glass, metal, plastic, and flexible pouches.
The Barriquand Steriflow (Attachment 10) has been the cascading water system most often encountered by FDA.
The Steriflow is an over-pressure retort designed to operate at high temperatures, at or above 130° C (265° F), at pressures of up to 84 psig (5.9 kg/cm2), with very short cook times. The over-pressure is supplied by compressed air and controlled separate from the retort temperature. The Steriflow uses less water for processing when compared to a water immersion retort, (e.g. 100 liters per basket in the standard 1300 mm model retort). At the start of processing the process water is added to the bottom of the retort shell. A gate in the bottom front of the retort shell prevents the loss of processing water when the retort door is opened. During processing this water is drawn from a trough in the bottom of the retort by a centrifugal pump capable of recirculating the water in the system approximately once every 9 seconds. The processing water passes through an indirect heat exchanger where steam is used to heat the water to processing temperature. The processing water then exits the heat exchanger and enters a water distribution manifold above the crates and containers. The processing water is forced through a series of small holes (e.g. 4 mm (5/16") on 21 mm (13/16") centers) in the manifold and cascades down over the crates and containers. At the conclusion of the thermal process, cold water is introduced into the heat exchanger to cool the processing water. The same water used to process the containers is used to cool the containers. The cooling water in the heat exchanger is never in contact with the containers. This provides for the use of low quality water (such as sea water) in the heat exchanger as the cooling medium.
Water entry into the water distribution manifold has been noted to be at the center or the end of the manifold in different models of the Steriflow. Location of the manifold water entry may be important. Temperature distribution studies have indicated that the cold zone in the retort may be affected by the location of the water entry.
Process water is normally used throughout a production shift prior to being replaced. Small amounts of water may be added prior to each cycle to replace water lost when the door is opened and product is removed.
In the standard 1300 mm retort, solid sided, perforated bottom 33" x 34" x 30" high retort carts are normally used with perforated dividers [19 mm (3/4") on 25 mm (1") centers] between layers. Container orientation is normally vertical. Container orientation, size, shape and loading configuration may have an effect on temperature distribution.
Temperature and pressure may be controlled either by a cam programmer on older systems, by a microprocessor/computer on newer systems, or by manual control. Temperature is normally controlled through a Resistance Temperature Device (RTD) located at the exit end of the heat exchanger. A second RTD located at the entry to the circulation pump is used to drive the temperature recorder. A MIG thermometer should be installed at this location. The entry to the water circulation pump has been selected as the location of the coldest water being circulated in the retort during thermal processing. Pressure is controlled separately through feed back from a pressure transducer and operation of compressed air entry and pressure relief valves.
The production programs for some systems are designed to bring the coldest spot in the retort up to thermal processing temperature through a series of time/temperature steps to insure that the temperature in the retort is at or above the filed