212 BACTERIA AND OTHER MICROORGANISMS IN CHEESE 
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 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 characteristic of cheese. 
The relation of microdrganisms 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. JInall 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 theripen- 
ing. Since cheese is made from milk, it must necessarily contain 
from the outset many kinds of bacteria, and among them there is a 
considerable percentage of lactic acid organisms. For a number of 
days, sometimes for several weeks, these bacteria increase in num- 
ber. After this they decrease until, when fully ripened, they are 
very few, compared to their numbers at certain stages of the ripen- 
ing. 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 
