218 BACTERIA AND OTHER MICROORGANISMS IN CHEESE 
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 continued 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 
product. This trouble has been found to be due to a yeast which 
gets into the milk. 
Rusty Spot-—This is characterized by rusty, red spots on the 
outside and, indeed, not infrequently throughout the whole cheese. 
The cheese loses its value and may in the end become quite ruined 
if the trouble develops sufficiently. The cause is a bacterium B. 
rudensis. 
Many other ‘‘faults’’ may be recognized as interfering with the 
normal ripening. Black spots and blue spots are sometimes noticed 
and a variety of “‘off” flavors that cannot be described. In regard 
