464 MICROBIOrOGY OF SPECIAL INDUSTRIES 



of bacteria tolerant of the high percentage of cane sugar, or from 

 yeasts, - 



Sterilization 



Economic Considerations. — For certain classes of food products, 

 pasteurization is widely applicable, and is of immense value from an 

 economic standpoint. Preservation by pasteurization is at best, how- 

 ever, temporary. Spores of spore-forming bacteria are certain to be 

 present on many kinds of foods, and these, unharmed by pasteurizing 

 temperatures, develop vegetative cells, and spoilage occurs. 



For permanent preservation, therefore, sterilization must be adopted 

 and it is upon the principle of sterilization, coupled with prevention of 

 future contamination by hermetically sealing the container, that the 

 whole canning and preserving industry is based. The method is 

 applicable to nearly every class of food, and with less alteration in the 

 food than any other method of conservation. The principle employed 

 to-day is essentially the same as that used by Appert over 100 years 

 ago. Although he knew nothing of microorganisms or their relation to 

 the spoilage of food, Appert's experiments taught him that not only 

 must the food to be conserved be heated thoroughly, but that it must 

 be so sealed as not to allow air to enter the container. In the light of 

 microbiological science, it is clear that the success of the process depends, 

 not upon keeping out the air, but upon keeping out organisms which are 

 carried in the air. 



SpECiric Application. — ^The process of preservation by steril- 

 ization is not so extensively -practised for fruit juices and fermented 

 liquids as that of pasteurization. If too high temperature is employed 

 for fruit juices, certain compounds of agreeable taste and aroma are 

 destroyed, with a consequent deterioration in the flavor of the product.' 

 Fruit juices may, however, be sterilized by heating at a low temperature 

 for several successive days. 



The method of Appert has its widest application in the conservation of fruits and 

 vegetables, meats and fish. Whatever modifications are made in the handling of the 

 different classes of foods the essentials are the same. The raw material after 

 thorough cleaning and removal of waste if any, is filled into the cans and submitted 

 to the sterilizing process, the degree of heat and time of processing varying with 

 different products. From the character of the flora, fruits as a rule require a com- 

 paratively low temperature for sterilization, while some vegetables and meats re- 



