CHAPTER XIV. 



BACTERIA AND OTHER MICROORGANISMS IN 

 CHEESE. 



CHEESE-RIPENING. 



Cheese consists primarily of the casein and fat of milk, collected 

 first as a curd and then allowed to undergo a series of chemical 

 changes called ripening. Ordinarily the casein is precipitated 

 from the milk by rennet, although it is done in some types of cheese 

 by simple souring. Then the curd is separated more or less from 

 the whey, and pressed into definite shape. The whey removes 

 most of the milk-sugar, and the cheese retains about two-thirds 

 of the food material in the milk, and since it is in a very dense form, 

 it is one of the most nutritious of our foods. The popularity of 

 cheese as a food depends rather upon its flavor than its food value 

 and the flavor develops during the ripening. Cheese-ripening 

 is a very complex phenomenon and one as yet only partly understood. 

 This is due partly to the intricacy of the subject and partly also to 

 the fact that there are very many different kinds of cheeses, and the 

 ripening of the different types is not by any means the same. Al- 

 though there are some hundred varieties of cheese, they may be ar- 

 ranged fairly well into two groups: i. The hard cheeses, and 

 2. The soft cheeses. The ripening of the hard cheeses is very dif- 

 ferent from that of the soft, and the ripening of the different types 

 of soft cheese varies greatly one from the other. Each kind of 

 cheese must, therefore, be studied as a special problem. 



Chemical and Physical Changes. During the ripening, 

 the cheese, which is at first rather hard, tough and elastic, gradually 

 becomes softer. The extent of this softening depends largely 

 upon the amount of water present, and, in the soft cheese, with their 

 large amount of water, a slimy and almost liquid consistency may 



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