CHAPTER XV 

 THE PRESERVATION OF FOODS 



It is impossible to handle foods in such a manner as to 

 prevent microorganisms from coming in contact with them. 

 With greater or less rapidity, depending on whether the or- 

 ganisms find in or on the food favorable conditions for 

 growth, decomposition changes will ensue and the food be 

 rendered worthless. In a previous chapter the ways in 

 which foods become seeded with microorganisms were stud- 

 ied. The more cleanly the conditions under which foods 

 are handled, the smaller will be the number of organisms 

 brought in contact with them, and the less rapidly will the 

 changes take place. The greater the number of organisms 

 initially present, the more rapidly the decomposition 

 changes occur, other conditions remaining constant. Hence, 

 one of the chief ways of preserving foods is to prevent their 

 contamination with germ life. But mere prevention of 

 contamination is not sufficient and must be supplemented 

 by other means, which may be divided roughly into three 

 classes: the removal of microorganisms from foods; their 

 destruction; and the establishment of conditions that will 

 retard or prevent their growth. These methods may be 

 used singly or in combination. 



The microorganisms that adhere to the surface of solid 

 foods may often be removed in large part by washing. 

 Microorganisms are practically always contained in dirt 

 and other matter foreign to the food. Consequently, the 

 removal of this dirt will tend to reduce such contamina- 

 tion. Washing or wiping of fruits, such as apples, tends 

 to remove the molds that are concerned in rotting processes ; 



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