THE HARD CHEESES. 197 



as due to the end-products of decomposition. The peptones and 

 proteoses that result from the digestion of the caseins do not them- 

 selves 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 charac- 

 teristic of cheese. 



The relation of microorganisms to the ripening of hard and soft 

 cheeses is so different that they must be considered separately. 



THE HARD CHEESES. 



These include many varieties, the best known of which are the 

 Cheddar cheeses (the most common in America), the Swiss 

 cheeses, and the Edam cheeses of Holland. In all these cheeses the 

 water is pressed out of the curd as completely as possible so that the 

 resulting cheese is very dense. In spite of its dense consistency, a 

 development of bacteria goes on for many days during the ripening. 

 Since cheese is made from milk, it must necessarily contain from 

 the outset many kinds of bacteria, and among them there is a con- 

 siderable percentage of lactic acid organisms. For a number of 

 days, sometimes for several weeks, these bacteria increase in number. 

 After this they decrease until, when fully ripened, they are very few, 

 compared to their numbers at certain stages of the ripening. A 

 single example will illustrate. Fresh cheese contained 6,600,000 

 per gram, when four days old, 51,000,000 per gram, and when four 

 months old, 1,000,000 per gram. 



It is the lactic acid bacteria that are most persistent, and while 

 in the early stages of the ripening other types are abundant, in the 

 fully ripened cheese, or even the half ripened cheese, there are usually 

 none left except the lactic acid bacteria. While there are variations 

 in the bacteria in different kinds of cheese and in different specimens 

 of the same variety, the above represents the general history of their 

 growth, and in all cases it appears that the lactic acid organisms are 

 finally found alone. 



It must be confessed that we do not yet know very much about 

 the part bacteria play in the ripening of the hard cheeses. That 



