178 Dairy Bacteriology. 



made from milk containing few or no lactic bacteria is 

 likely to develop a bitter taste, due to the growth of the 

 digestive bacteria that are able to grow through the lack 

 of acid in the cheese. 



If the milk contains considerable numbers of yeasts, 

 a sweet or fruity flavor is apt to develop, due to the prod- 

 ucts of the fermentation of the sugar by the yeast. This 

 flavor resembles that of fermented fruit, or the bouquet 

 of certain kinds of wine. 



Putrid cheese. In the absence of acid-forming bac- 

 teria, the cheese may develop a putrid or rotten odor, due 

 to the growth of some types of putrefactive or digesting 

 bacteria. This trouble is very infrequent in cheddar 

 cheese, since this is made from ripened milk, but occurs 

 more frequently in those types in which no acid is devel- 

 oped. 



Bacteria develop in the cheese in colonies or masses, 

 just as they do in the plate cultures of the bacteriologist, 

 made with transparent media, such as gelatin. Cheese 

 is opaque ; therefore, the growing colonies cannot be read- 

 ily discovered, but when pigment-forming bacteria grow 

 in the cheese, their presence is likely to be noted, because 

 of the colored spots that are formed. 



Rusty spot. The "rusty spot" that has been encoun- 

 tered in New York and Canada is due to one of the 

 colored bacteria which produces an orange or yellowish- 

 red pigment. Various other pigment-forming organisms 

 have been met in cheesy, each producing its colored col- 

 ony which differentiates itself from the mass of the 

 cheese. If the pigment is produced in considerable 

 quantities, and is soluble in any of the constituents of 

 the cheese, the color will not appear in spots but will be 

 more diffuse, or may impart a color to the entire mass. 



