Evaluation of thermal processes for canned foods has been a subject of scientific research for some 25 years. The General Method, f o r calculation of thermal processes, described by Bigelow, Bohart, Richardson, and Ball (1920), was the first scientific approach to the problem of applying bacteriological and physical data to the evaluation and calculation of thermal processes. This method is still used in the canning industry, especially for evaluating processes for foods for which the heating curves cannot be represented by one or two straight lines-Schultz and Olson (1940). Simpler and more versatile methods for process calculation were developed by Ball (1923Ball ( , 1928. Ball's methods have been used extensively in the canning industry. The simplicity and flexibility of the methods have contributed greatly toward the solution of many practical processing problems. Numerous simplifications and improvements in the above methods of process calculation and evaluation have been made by Schultz and Olson (1938, 1940), Olson and Stevens (1939), and Jackson and Olson (1940). ' By the procedures for process evaluation now available, it is possible to assign relative sterilizing values to heat processes used in the manufacture of practically all canned foods. The.F values, obtainable by mathematical treatment of physical and bacteriological data, express in simple numbers the relative effectiveness of different heat processes for canned foods. However, because of the great variation in thermal resistance of bacteria, it has not been possible to establish a generally applicable rule for ascertaining whether a given process will always, or even most of the time, prove satisfactory and desirable for a given product manufactured under conditions of practical operation.The thermal resistance of any species of bacteria varies with many factors, one of the most important of which is the nature of the substrate in which the bacteria are subjected to heat. Among other factors which 1 may influence the thermal resistance of any given species of bacteria are initial concentration of cells, presence or absence of heat-resistant spores, and age of bacteria. In meat, the picture is complicated by the fact that many different species of bacteria contaminate the product under conditions of practical operation.If the rate at which heat penetrates a can of food and the nature of the thermal death time curve for a given organism in that food are known, In this and future papers only those meats which are hermetically sealed in the can and given. heat processes designed to prevent their spoilage in the course of commercial handling without special treatment will be considered as canned meats.Present address : Michigan State Department of Health, Lansing, Michigan.
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