CHAPTER III* 



THE RELATION OF MICROORGANISMS TO CHEESE 



GENERAL 



Cheese consists of the fat and casein of milk, together with the 

 insoluble salts; however, along with these constituents are carried 

 some of the moisture of milk, in which are dissolved small quantities 

 of sugar, albumin, and salts. The amount of moisture and soluble 

 constituents found in cheese is determined by the amount of whey 

 incorporated in the curd. 



In the process of making cheese, it is necessary to curdle the milk, 

 thus enabling the separation of the casein and fat from the milk serum. 

 Two methods are employed to accomplish this purpose, and, as a 

 result, two types of cheeses are produced. 



TYPES OF CHEESE 



These types may be designated as "Acid-curd Cheeses" and "Rennet- 

 curd Cheeses" 



ACID-CURD CHEESES. The curdling may be accomplished by 

 allowing the milk to undergo acid fermentation, either spontaneously 

 through the action of the normal flora of the milk, or through the 

 addition of pure lactic cultures. Most acid-curd cheeses are ready 

 for use as soon as the whey has been removed by draining and the 

 curds salted. Acid-curd cheeses are not commercially important. 

 They are made for local consumption and are to be classed as a form 

 of sour milk. They owe their flavor to the products of the acid fer- 

 mentation, especially lactic acid. The moisture content is high, 

 which, together with the acid reaction, favors the growth of molds 

 and yeasts. These biological agents may soon spoil the cheese. 



RENNET-CURD CHEESES. All of the important varieties of cheeses 

 are made by the use of rennet for the curdling of the milk. Over 



* Prepared by E. G. Hastings. 



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