Bacteria and Cheese Making. 171 



If the sugar is fermented by some organism that does- 

 not form acid, as the lactose-fermenting yeasts, the 

 cheese does not ripen. The lactic bacteria are therefore 

 an essential factor in inaugurating the ripening changes 

 in all types of rennet cheese. 



Preservative action of acid. In a previous chapter it 

 was shown that raw milk does not undergo putrefaction, 

 because of the restraining effect of the acid formed by 

 the lactic bacteria on the putrefactive organisms. This 

 same phenomenon is noted in cheese. Milk always con- 

 tains putrefactive bacteria which pass into the cheese,, 

 but they cannot grow therein because of the high acidity. 

 In the absence of the acid-forming organisms in the 

 cheese, the cheese may remain tough and rubbery, on 

 account of the lack of suitable conditions for the action 

 of the pepsin of the rennet extract, or when the milk con- 

 tains large uumbers of digesting organisms, the cheese- 

 may develop a putrefactive condition, as noted by the 

 offensive odor and soft pasty texture. 



Other factors concerned in cheese ripening. There 

 are other factors that are also concerned in the complex 

 series of ripening changes noted in cheddar cheese. All 

 animal fluids and tissues, if kept under perfectly sterile 

 conditions at ordinary temperatures, will undergo a cer- 

 tain amount of decomposition, due apparently to their 

 content in enzymes that have a digestive action. Meat 

 kept in storage becomes more tender due to the softening 

 of the connective tissue. Milk, derived as it is from 

 actively secreting cell tissue, gives certain reactions that 

 are common to living material. If chloroform, which 

 restrains the action of bacteria, but does not prevent the 

 activity of enzymes, is added to it, it will curdle in the 

 course of a few weeks and will become partially digested. 



