226 PRACTICAL DAIRY BACTERIOLOGY 



Flavors. The production of flavors is of no less importance 

 than the chemical digestion of the cheese. At the present time, 

 however, there is a very profound ignorance concerning the 

 real source and cause of cheese flavors. They are without doubt 

 the products of decomposition. They appear in the cheese 

 only toward the end of the ripening process, and are regarded 

 generally as due to the end products of decomposition. The 

 proteids and proteoses, that result from the digestion of the 

 caseins, do not themselves have any of these peculiar cheese 

 flavors; but toward the end of the ripening some of the material 

 seems to be still further broken down into the simpler end 

 products which show the flavors characteristic of cheese. The 

 nature and cause of these flavoring substances we do not def- 

 initely know, but further reference to the matter will be made 

 later. 



BACTERIA IN CHEESE RIPENING 



In studying the relationship of micro-organisms to cheese 

 ripening, we can best understand the subject if we consider 

 separately the chief types of cheese. There is no question but 

 that the ripening processes of hard and of soft cheeses, although 

 phenomena somewhat closely related, are very different from 

 each other, and are produced by very different agents. We shall 

 understand the subject better if they are considered separately. 



Sour Milk Cheese, Dutch Cheese, etc. There is one type of 

 milk product, commonly called cheese, that is not in any proper 

 sense a true cheese. Under this head are included cheeses that 

 consist of nothing except the curd of sour milk. In making 

 them the milk is allowed to sour under the action of the lactic 

 acid bacteria until it is well curdled. 1 Sometimes, however, a 

 little rennet is added to the milk in order that the curdling may 

 occur more quickly than it would under the action of the lactic 

 bacteria alone.- After being thus curdled, the curd is separated 



1 Hall, Van Slyke and Hart. Bui. 245, N. Y. Exper. Sta., 1904. 



