In addition to the temperature differential between the heating or cooling medium and the product, the factors that directly affect the heat penetration are the the nature of the product, type of container, and heating or cooling medium. As the heat penetration test should employ test units representing the worst case situation (i.e., slowest heating), considerable information on the product as it will be in the container should be available so that all variables can be considered. Quantitative data on variability and mean values should be determined and recorded where appropriate.As changes in the product composition can affect the heat penetration,the product formulation should be kept consistent for a given set of processing conditions. Any alternate ingredients or components should be considered when formulating the worst case situation for the test containers.The sizes, shapes, and weights of solid components should be measuredand their variation expected to occur during normal operations determined. These can exhibit considerable variation depending on the type of solid component and the manner in which it has been prepared. As some products may shrink in size during the thermal process (e.g., meats; Chap.7) and others may swell (e.g., beans; Chap. 5), the degree to which this willoccur should be known and taken into account.The consistency or viscosity of any sauce or liquid component should also be kept constant, and any variations normally encountered in day-to-day operations should be determined so that they can be used in constructing the worst case. The type of thickening agent used (e.g., starch, gum, etc.), its concentration, and reaction to heat, are important factors in product consistency (CFPRA, 1977). Concentrations and types should be kept constant. Changes in product consistency or viscosity during thermal processing will certainly affect the heating characteristics. Some products, such as vegetable soups, noodle soups, cream soups, chowders, and so on, which contain starch, exhibit an uptake of the surrounding liquid during the heating process or may undergo a phase change such as starch gelatinization (Pflug, 1975). This phenomenon represents a complex heating product that can undergo a complete shift from convection heating to conduction heating. Extreme caution should be taken in case of slight variations in product formulation or ingredients that would cause the shift to conduction heating to occur at a different time or temperature; also it would change the overall heat penetration data. Consequently, special care should be taken to identify and control specific variables related to heating rates of these types of products.Changes in blanching conditions (Chap. 5) may cause swelling/matting or shrinkage of food products. Blanching and other preparatory methods should be the same as those used in commercial practice; in fact, the product used for the test units should be derived from the normal
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