MICROBES IN CHEESE-MAKING. 149 



value whatever. Incidentally, it is true that the cheese also furnishes 

 a considerable amount of food material. Thus it nourishes as well as 

 stimulates and delights; but, after all, we must recognize that its chief 

 value is in its flavor rather than in its nutritive quality. 



Hence it becomes a very significant question to inquire into the 

 source of this flavor. We find, first, that the cheese as originally made 

 possesses no flavor, or, at least, none of that peculiar flavor which we 

 know as cheesy. Cheese is made from milk by causing the casein in 

 the milk to be precipitated, i. e., causing the milk to curdle, commonly 

 by the addition of rennet, or, in so-called Dutch cheeses, by simply 

 allowing the milk to sour. The precipitated casein is then separated 

 from the liquids of the milk, and the curd, when subsequently pressed 

 and molded, becomes the cheese. But the freshly-made cheese possesses 

 no flavor, nor does the flavor develop to any degree until after it has 

 passed through a process known as 'ripening.' The ripening of cheese 

 may take several days or several months, or, in some cases, one or two 

 years; but the flavor always arises during this process. Moreover, the 

 various cheeses with their varieties of flavors are mostly made from the 

 same kind of milk, but are subjected to different modes of ripening, and 

 the distinctive quality in the endless types of cheeses is due in large 

 measure to differences in the method of bringing about this ripening. 

 Clearly enough the flavor is a product of cheese ripening, and if we wish 

 to find the source of these most valuable flavors we must seek it in the 

 ripening process. 



This cheese ripening proves to be a two-fold process. The first 

 change in the cheese is a chemical one, which results in altering the 

 chemical nature of the cheese in such a way as to render it more easy 

 of digestion. This change appears to be due in part to a certain ferment 

 which is found in milk. This material belongs to the class of chemical 

 ferments or enzymes and is a normal constituent of milk, although 

 its presence was not mistrusted until recently pointed out by two 

 American investigators. With the chemical changes produced by this 

 enzyme we are not here particularly concerned. It is certainly not the 

 cause of all the flavors which develop in the cheeses, and, therefore, 

 this character of the ripened cheese must be chiefly attributed to another 

 factor. There is no doubt that this other factor is a living one. The 

 flavors can generally be traced directly to the growth upon and within 

 the cheese of a variety of plants; and the ripening is carried on in a 

 fashion designed, at the same time, to stimulate the growth of some 

 species of plants and to check the growth of others. 



Cheeses are of two kinds, hard and soft. As implied in the name, 

 there is a difference in the consistency of the cheese. But this is not 

 all; for on account of the methods of manufacturing, the ripening is 

 produced by different classes of plants in the two classes of cheeses. 



