3Q2 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



reasons previously stated it is impracticable for use on a commercial 

 scale. The difficulty from erosion in tins is partly overcome by coating 

 the interior of the can with an enamel or lacquer which is not affected by 

 the heat of sterilization, nor by chemical action of the contained material 

 within a reasonable length of time. 



DEGREE OF HEAT REQUIRED. The actual sterilization of food 

 products after placing in the containers is termed by the commercial 

 canner processing, and he appreciates fully that upon the care with which 

 the processing is done depends the success of the entire pack. The 

 degree of heat necessary to accomplish sterilization varies considerably 

 with different products. 



One factor lies in the chemical composition of the fruits or vegetables 

 to be sterilized. It is, for example, well known that peas and asparagus 

 are rendered germ-free with much greater difficulty than beans, not- 

 withstanding the fact that the heating of the can contents of the former 

 is accomplished much more easily than that of the latter. The higher 

 acid content of the beans facilitates the sterilization, and this same prin- 

 ciple holds true in a broad way for all products of an acid character. 

 The canner and the housewife have long known that tomatoes were 

 easy to preserve as compared with other vegetables. The canner also 

 finds a variation from season to season. In some seasons the acid content 

 of fruit and vegetable products will be higher than in others, and conse- 

 quently a lower processing temperature will suffice for sterilization. 



In sterilization under pressure, as in the canners' retort, it is important 

 that the steam forced into the autoclaves should completely displace all 

 the air, for otherwise at a certain pressure the corresponding temperature 

 will not be obtained. Large cans require a longer time for thorough 

 heating than small cans; closely packed cans are heated with greater 

 difficulty than loosely packed ones; the inner temperature is frequently 

 lower than that of the outer parts of the can. 



In addition to these factors, the canner must consider the possible 

 presence or absence of bacterial spores, which may gain entrance to his 

 factory, and necessitate a higher temperature than that usually employed 

 to accomplish the desired result. 



STORAGE. Canned goods should be stored in a cool temperature. 

 With some foods, there is a slow physico-chemical change occurring even 

 in the absence of microorganisms by which the texture is loosened with 

 consequent deterioration in value. These changes proceed very slowly, 



