182 Dairy Bacteriology. 



four to thirty-six hours. As the rennet contains acid- 

 forming organisms, these grow rapidly in the warm 

 whey, so that by adding this sour whey to the milk, the 

 maker is not only adding rennet, that is to curdle the 

 milk, but also a small starter of lactic bacteria. If the 

 rennet thus prepared contains no harmful bacteria and 

 the milk is of good quality, the cheese is likely to ripen 

 in a normal manner. The rennet should be prepared 

 with due regard to bacteriological principles, a condition 

 that is rarely met in Swiss factories in this country. 



Swiss cheese has two striking characteristics, the flavor 

 and the presence of holes or "eyes. " The flavor is 

 sweetish rather than the sharp and pungent flavor of 

 cheddar cheese. The bacteria concerned in its produc- 

 tion are not known, but it is certain that specific organ- 

 isms play some role, since if the flora of the cheese is 

 changed by salting the curd or by the use of milk con- 

 taining large numbers of lactic bacteria, the flavor will 

 also be changed. This role of the acid-forming bacteria 

 in Swiss is the same as in cheddar, i. e., through the acid, 

 conditions are established for peptic action, the curd be- 

 ing partially digested while at the same time the curd 

 mass is protected from putrefactive processes. 



In Swiss cheese during the ripening process, holes 

 about the size of a large cherry develop which should be 

 quite uniformly distributed throughout the cheese. The 

 inner surface of the hole is glistening and, in a well- 

 ripened cheese, a small quantity of clear brine, i. e., 

 " tears" may be noted. These holes or "eyes" may be 

 called the trade mark of the Swiss cheese, since without 

 them the product has a lessened commercial value, even 

 if it possesses the typical flavor. The ' l eyes' ' are caused 

 by bacteria that ferment the lactic acid produced by the 



