388 MICROBIOLOGY OF SPECIAL INDUSTRIES. 



organisms, it is said to keep indefinitely if unopened, and will even keep 

 for a number of days after opening. Occasional losses do occur, however, 

 by spoilage of the finished product, either from the growth of occasional 

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

 yeasts (p. 363). 



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, however, 

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

 on many kinds of foods, and these, unharmed by pasteurizing tempera- 

 tures, 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 essen- 

 tially the same as that used by Appert 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. 



SPECIFIC APPLICATION. The process of preservation by sterilization 

 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 steriliz- 

 ing process, the degree of heat and time of processing varying with different products 



