ENZYMES IN CHEESE RIPENING. 225 



cheese. This has been proved by subjecting milk to the 

 action of ether vapor which prevents bacteria growth, but does 

 not prevent the action of the enzyme. Under these circum- 

 stances, although bacteria do not develop, a series of chemical 

 changes occur in the casein similar to those of the ripen- 

 ing of cheese. Besides galactase, there is also a second 

 enzyme present in cheese made in the ordinary manner. The 

 rennet, which is commonly used for the curdling of the milk, 

 is obtained from the stomach of young mammals. In the 

 stomach of the same mammals there is always present a 

 second enzyme, pepsin. Pepsin also has a digestive action 

 upon casein somewhat similar to that of galactase, forming 

 soluble materials of the insoluble proteids. As ordinarily 

 prepared, rennet will always contain some of this pepsin, 

 which will be added to the cheese. 



Cheese thus commonly contains two enzymes capable 

 of slowly changing the nature of the casein. To what 

 extent is the ripening produced by the action of these 

 enzymes and to what extent by the development of bacteria ? 

 Although at the present time this question is not fully 

 answered, a somewhat general consensus of opinion appears 

 to have been reached. A brief summary of the conclusion 

 held is as follows : 



In the ripening of both hard and soft cheeses enzymes * 

 undoubtedly play a part in producing the solubility of the 

 casein, since cheeses will undergo certain parts of the ripen- 

 ing process without the development of microorganisms. On 

 the other hand, it has become evident that the normal ripen- 

 ing of cheese demands, in addition to the enzyme action, the 

 aid of microorganisms. When cheeses are ripened in the 

 presence of chloroform, which prevents bacteria growth, a 

 ripening takes place, but not a normal one (250). The 

 invincible conclusion is that the normal ripening requires the 

 development of microorganisms. Moreover, Freudenreich 

 has made cheeses out of milk drawn from a cow under 



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