468 mcsoBioEOGY op special industries 



The degree of heat necessary to accomplish sterilization varies con- 

 siderably with different products. 



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

 to be sterihzed. 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 consequently a lower processing temperature will suffice for 

 sterilization. ' 



In steriUzation under pressure, as in the canners' retort, it is impor- 

 tant that the steam forced into the autoclaves should completely dis- 

 place all the air, for otherwise at a certain pressure the corresponding 

 temperature will not be obtained. Large cans require a longer timie for 

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

 greater diffidulty 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 em- 

 ployed to accomplish the desired result. > 



Home Canning of Foods 



The successful canning of foods in the home depends upon the 

 same principles as those employed in commercial canning, namely, 

 cleanhness, soundness of raw material, and complete sterilization. 

 Aside from the universally used open kettle method of handling the 

 foods, two other methods are now widely used: the cold-pack method, 

 and the vacuum-seal method. In the cold-pack method, the products 

 are packed cold in their fresh natural state into the glass jars or other 

 containers. To the fruits, hot syrup is applied; to the vegetables and 

 greens hot water and a little salt is added. Then the sterilization 

 is done in the jars after they are partially or entirely sealed. Steriliza- 



