BACTERIA IN CHEESE 199 



Adametz^ was one of the first to isolate the cheese bacteria. 

 Wider investigation led the same worker to the conclusion that 

 these bacteria operated on the ripening of milk, not only through 

 the peptonisation of casein, but also through the arrest of the 

 fermentation of milk-sugar. The fermentation of milk-sugar 

 leading to formation of acid and coagulation, can be obtained 

 by different bacteria {Staphylococci^ Sarcince, B. coli, and members 

 of the B. subtilis group). Spontaneous coagulation of milk is 

 chiefly caused by B. cerogenes, and other closely related bacteria 

 — occasionally also by B. coli imuiobilis (Flugge). 



At present it is generally held that the ripening changes 

 consist of two processes, namely, chemical changes set up by 

 ferments, affecting the solubility of the curd, and bacterial changes, 

 producing the flavour of the cheese. Freshly precipitated casein, 

 as we have pointed out elsewhere, is insoluble and difficult of diges- 

 tion. During ripening it becomes converted into soluble bodies, 

 the change being brought about in part by unorganised ferments 

 (enzymes), such as galactase (Babcock and Russell), and casease 

 (Weigmann, and others), and in part by bacteria. It is with the 

 latter that we are concerned, though it should not be forgotten 

 that both are essential to cheese-making. In the second place 

 there is the ripening, and that is probably wholly due to bacteria.- 



The Number of Bacteria in Cheese 



The number of bacteria in cheese is naturally less than that 

 present in milk or cream. The closer texture and consistence of 

 cheese, coupled with the lessened degree of moisture are sufficient 

 factors to account for this. Nevertheless cheese contains a consider- 

 able number of organisms. Adametz found that freshly precipi- 

 tated curd, moulded in the press and freed from excess of whey, 

 contained between 90,000 and 140,000 micro-organisms per gramme, 

 a comparatively large number of them having the power of liquefy- 

 ing gelatine, or in other words they possessed a peptonising ferment. 

 During the period of ripening the bacterial content of the cheese 

 gradually rose to 850,000 in Emmenthaler cheese, and 5,600,000 

 per gramme, in a soft household cheese.^ Only a small percentage 



* Land. Jahrb., 1889. 



^ See also Centralb.f. Bakt., 1901, vii., p. 187. 



^ Soft cheeses (Camenbert, Brie, etc.) are made by moulding the curd but 

 not subjecting it to great pressure or heat. They ripen rapidly and decay 

 readily. Hard cheeses, on the other hand, are cut in the curd to release the 

 superfluous whey and subsequently subjected to 1 10" F. and heavy pressure. 

 They keep well and form the chief cheeses of commerce. 



