2O2 BACTERIA AND OTHER MICROORGANISMS IN CHEESE. 



in Chapter XI as Bact. aerogenes type. As pointed out in that 

 chapter, the different varieties of this type vary much in the amount 

 of gas they produce; sometimes the quantity is very slight, sometimes 

 it is extraordinarily large; and it is easy to understand how different 

 strains and different quantities of bacteria will produce-grades 

 of gasiness in cheeses. 



Bitter Cheese. The development of a bitter taste is one of 

 the common troubles of cheese-makers. Sometimes this defect will 

 involve the whole output of a cheese factory and cause heavy losses 

 for a considerable period. Two different causes have been deter- 

 mined upon as responsible for the trouble. In one extended series 

 of losses thus resulting, the cause was found to be a yeast (Torula 

 amari Fig. 37) that obtained access to the cans and vats and con- 

 tinued for a long time to make trouble. The difficulty disappeared 

 with the thorough cleaning and sterilizing of all articles in the dairies 

 and factories. In another series of bitter cheeses the trouble was 

 found to be in one of the liquefying bacteria. This class of organisms 

 is nearly always present in milk, and though the growth of the lactic 

 bacteria usually crowds them out, sometimes, either because of 

 their extra abundance and vigor or because of lack of sufficiently 

 vigorous acid organisms, they are not overgrown by the lactic acid 

 bacteria, but continue to multiply until they develop bitter flavors 

 that injure or spoil the cheese. This cause of bitterness has been 

 detected in both the hard and the soft cheeses. 



Putrid Cheese. Sometimes soft spots appear upon the surface 

 of a cheese. They may become larger, eating their way into the 

 cheese, and producing a more or less slimy appearance. The 

 trouble is undoubtedly due to the growth of putrefying bacteria, 

 but not much is known about the matter at present. 



Fruity or Sweet Cheese. This is a phenomenon which occurs 

 sometimes over widely extended .districts and detracts from the 

 character of the cheese without always ruining it. It is character- 

 ized by a peculiar sweet taste, which, although not unpleasant, 

 spoils the flavor of the cheese and thus injures the sale of the prod- 

 uct. This trouble has been found to be due to a yeast which gets 

 into the milk. 



