CHEESE 615 



still limited, owing to our fragmentary knowledge of the biologic 

 reactions involved. In a few cases, however, cultures have proved 

 very successful. The Institut Pasteur is placing cultures on the 

 market for ripening Camembert cheese. Camembert cheese made 

 in this country is also ripened by the aid of cultures. Cultures of 

 lactic streptococci are used in Holland for making Edam cheese; 

 in Switzerland cultures of lactobacilli are used for making Em- 

 menthaler cheese. It is not unreasonable to assume that in the 

 course of time a variety of cheeses will be made under one roof, 

 where the manufacture will be controlled by the use of special 

 cultures. It has happened, however, in places where more than 

 one type of cheese is prepared that so-called "bastards" have 

 resulted by accidental contamination of one kind of cheese with 

 cultures intended for another. 



Bacteria of cheese originate from the milk, rennet, water, air, 

 and utensils. Bacteria from the milk are obviously the most 

 important. As to the bacteria from rennet, the number and 

 kinds depend upon the kind of rennet used. In European rennet 

 there are millions of bacteria, and among them lactobacilli. This 

 rennet is prepared by making an extract of calves' stomachs with 

 sour whey. Lactobacilli are numerous in the digestive tract of 

 calves and in sour whey. They are, therefore, present in the ren- 

 net extract. Rennet used in this country is prepared by extraction 

 of the fourth stomach of a calf with salt solution and contains a 

 negligible number of bacteria. Rennet extract contains a pepsin- 

 like enzym which digests casein when acid is present. This 

 enzym is activated by the lactic acid contained in the curd. 



Bacteria from water, air, and utensils do not assume impor- 

 tance if proper cleanliness is exercised. If such cleanliness is neg- 

 lected these bacteria may cause the cheese to-be of inferior quality. 



The distribution of bacteria in cheese is fairly uniform in initial 

 stages of ripening, but later on they are more concentrated in some 

 places than in others, so that ripening does not proceed uniformly 

 throughout the cheese. Streptococci and lactobacilli are most 

 prominent in inner portions, while micrococci are common on the 

 outside. In ripe Cheddar cheese there are chiefly lactobacilli, 

 while in fresh Cheddar cheese streptococci are predominant. 

 When the curd is prepared 70 to 80 per cent, of the bacteria in 

 the milk are enclosed in the cheese. When the curd is pressed, 

 however, some of these bacteria are expelled with the whey. 

 Lohnis states that in young Emmenthaler cheese 500,000,000,000 

 bacteria are present in 1 gram of the slimy outer layer, and that 

 this layer consists almost entirely of bacteria. Lactic strepto- 

 cocci are by far the largest group of organisms present in "green 

 cheese." They act on the milk-sugar which remains dissolved in 



