Guide to Inspections of Low Acid Canned Food 11
Manufacturers - 2
and (iii). The firms scheduled process should be used to evaluate the thermal process for that product.
Initial temperature (I.T.) is defined in 21 CFR 113.3 (l) as the average temperature of the contents of the coldest container to be processed at the time the thermal processing cycle begins, as determined after thorough stirring or shaking of the filled and sealed container.
The initial temperature of the contents of one container to be processed must be determined with sufficient frequency to ensure that the temperature of the product is no lower than the minimum initial temperature specified in the filed scheduled process. The regulations do not require that the initial temperature of each retort load of product be checked. The closer that a firm operates to the minimum initial temperature in the filed scheduled process the more critical measurement of the initial temperature at frequent intervals becomes.
When initial temperature is measured in those products which incorporate frozen ingredients extra care may need to be taken to insure that the temperature reading is of the (average) temperature of the contents of the container and not just the temperature of the covering liquid. Initial temperature may have a significant effect on the thermal process delivered to the product, and the effect may be determined only through the analysis of process establishment data for that product.
Initial temperature is normally determined using a dial, electronic or other type of hand held thermometer. Glass stem thermometers are normally not used to determine initial temperature because of the potential risk of breakage. Firms have attempted to use pyrometers to measure initial temperature with mixed results. The use of pyrometer's to measure the outside temperature of a container to determine the initial temperature of a process requires adequate studies by the firm to document a correlation between outside container temperature and the actual product initial temperature in the container.
When determining the initial temperature of containers being processed by steam, a container is normally selected from one of the first containers going into the bottom layer of the first retort crate. This container is then set aside where it is not subject to extreme changes in temperature. At the time that the retort lid is closed and the steam is turned on the initial temperature in the container is determined. This same procedure is normally acceptable for all batch type retort systems except as noted. For those retort systems using water to cushion the fall of containers into the retort, or where water is in the retort prior to the addition of the containers, provisions must be made to insure that the temperature of the water does not lower the initial temperature of the containers. In those instances where water comes in contact with the containers prior to beginning the thermal process, the initial temperature of the process may be either the temperature of the contents of the container or the temperature of the water in the retort, whichever is the lowest. In systems that use cushion water, such as the crateless retort system, the initial temperature may be the temperature of one of the last containers to enter the retort, if the cushion water is maintained at a high temperature. For continuous retort systems a container should be obtained just prior to entry into the retort system for initial temperature determination.
Line breakdowns and processing delays may cause the initial temperature in containers to fall below the minimum scheduled initial temperature. During inspections of lacf manufacturers the investigator should determine the firms procedures for handling product in the event of thermal processing delays. When a product is placed into a retort that has to be cooled to restart the process, or to move the product to a second retort for processing, a new initial temperature may have to be determined.
CRITICAL FACTORS-MEASUREMENT EQUIPMENT
A variety of equipment is used to measure critical factors including: scales, thermometers, gauges, and consistency meters or devices. The accuracy of the equipment must be documented by the lacf manufacturer. There is no specific requirement in the lacf regulations that equipment used for the measurement of critical factors be checked for accuracy and calibrated as necessary. Good judgement however dictates that equipment used to measure critical factors be accurate. The investigator can determine the accuracy of scales, thermometers and gauges used to determine critical factors by making comparison measurements during the factory inspection. It is suggested that the manufacturing firm also make accuracy checks on their scales, and thermometers on a routine basis and that records of these checks be made. If a thermometer used to determine initial temperature or a scale used to determine fill weight is found to be out of calibration, the thermal process for the product for which the device was used may be in question back to the date that the measuring device was last checked for accuracy.