thermal processing temperature at the time that the retort thermal process begins. An example of a stepped program is as follows:
- Preheat water to 115° C (239° F).
- Heat from 115° C (239° F) to 137° C (279° F) 6 minutes (must meet both time and temperature).
- Heat for 136° C (277° F) 1 minute (time and temperature). This over-shoot temperature is used to help achieve adequate temperature distribution in the retort.
- Heat for 135>° C (275° F) 1 minute (time and temperature).
- Heat for 134>° C (273° F) 5 minutes (scheduled operating process temperature).
To obtain adequate temperature distribution the system is normally operated with a temperature overshoot of at least 1° C above the filed scheduled process temperature.
The stepped program varies with the retort, product and container. This program should be filed as part of the firm's filed scheduled process. Documentation that the steps in the come up portion of the retort program take place may be difficult. The come-up temperatures sensed by the microprocessor may not be the same temperatures displayed by the MIG thermometer and the temperature recording chart.
There are several areas of concern unique to the water cascade retort systems which should be addressed when inspecting these systems.
- The come-up portion of the process must be designed to provide for adequate temperature distribution (all parts of the retort are at or above retort temperature at the start of the thermal process hold time). The come-up requirements may differ from one product to another in the same retort, and from one container type to another in the same retort. Ideally temperature distribution studies should be performed on each retort model, each product produced, each container type used, and on each individual retort installation to determine the come-up procedures. The firm should have documented by temperature distribution studies that their come-up procedures result in adequate temperature distribution in the retort prior to the start of the timing of the scheduled process.
- Care should be taken to determine the location of the control and recording RTDs. The recording RTD has been noted to be installed in the exit end of the heat exchanger. This may provide a recorded temperature higher than the coldest temperature in the retort. At least one manufacturer now recommends that the control RTD be located after the heat exchanger, with a feed-back RTD located at the entry to the circulation pump. The latter RTD also drives the temperature recording instrument. Both RTDs should read at or above the scheduled process temperature prior to beginning the thermal process timing.
- FDA has noted that the Steriflow is not always equipped with a MIG thermometer. When modified for a MIG thermometer, the MIG thermometer should be installed in the inlet line of the circulation pump, next to the recorder RTD, to monitor the temperature of the return cold water, which is the average coldest spot in the retort. MIG thermometer lag will normally be observed during the come-up steps.
- Water flow is not normally controlled as a critical factor. A pressure differential may be measured between the pressure on the entry and exit ends of the water circulation pump. This pressure differential alarms the control system if the set limits are exceeded. The pressure differential is a measurement of the differences in pressure on the two sides of the pump and may not measure a true water flow. The pressure differential will indicate failure of the water pump but may not always indicate a clogged water distribution system. A flow measuring device is recommended to provide a more accurate measurement of actual water flow in the system. Water flow in the system must be the same as that used during temperature distribution studies in the retort.
- The processing records maintained by the firm must document that operating steps required to attain uniform temperature distribution in the retort during thermal processing are being met. These steps should be listed as critical factors on the firm's process filing form.
The holes in the water distribution manifold may become plugged with product or mineral deposits. There should be a program in place for routine maintenance and cleaning of return ports, the water distribution manifold, and water filter screens if present. During inspection of these systems the water distribution manifold should be examined to determine if the holes are plugged or have been reduced by mineral scale buildup.
The Phoenix cascading water retort operates in a manner similar to the Steriflow. The Phoenix retort system is offered in the U.S. by Allpax Products Inc. Mandeville, La. under the name Spray-Pax in still and rotational models.