202 BACTERIA AND OTHER MICROORGANISMS IN CHEESE. 
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in Chapter XI as Bad. 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. 
