CHAPTER III.* 

 THE RELATION OF MICROORGANISMS TO CHEESE. 



GENERAL. 



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

 uble salts; however, along with these constituents are carried some of the 

 moisture of milk, in which are dissolved small quantities of sugar, albu- 

 min, 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 cheese constituents from the bulk of 

 whey and soluble constituents of the milk. 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 maybe 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. This method furnishes the so-called acid-curd cheeses, 

 which are ready for use as soon as the whey has been removed by draining 

 and the curd salted. Acid-curd cheeses are not commercially important in 

 that 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 fermen- 

 tation, 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 four 

 hundred kinds are known, but only twelve to fifteen are of great com- 



* Prepared by E. G. Hastings. 



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