164 Dairy Bacteriology. 



Where rennet extract or tablets are used, as is gener- 

 erally the case in cheddar making, the number of bacteria 

 added is so infinitesimal as to be negligible. 



Development Of acid. In the manufacture of cheddar 

 cheese, the development of acid exerts an important influ- 

 ence on the character of the product. This is brought 

 about by holding the curds at temperatures favorable to the 

 growth of the bacteria in the same. Under these conditions 

 the lactic-acid organisms, which usually predominate, de- 

 velop very rapidly, producing thereby considerable quan- 

 tities of acid which change materially the texture of the 

 curds. This acid unites to some extent with the casein, 

 thereby producing compounds of a character different from 

 those existing in the green curds. The acid also ex- 

 erts a slight solvent effect on the casein, as is seen in the 

 " strings " made on the " hot iron." This causes the curds 

 to mat, producing a close, solid body free from mechan- 

 ical holes. Still further, the development of this acid is 

 necessary for the digestive activity of the pepsin in the 

 rennet extract. 



In some varieties of cheese, as the Swiss, acid is not de- 

 veloped and the character of the cheese is much different 

 from that of cheddar. In all such varieties, a great deal 

 more trouble is experienced from the production of " gassy " 

 curds, because the development of the gas-producing bac- 

 teria is held in check by the rapid growth of the lactic acid- 

 producing species. 



Bacteria in green cheese. The conditions under which 

 cheese is made permit of the development of bacteria 

 throughout the entire process. The cooking or heating of 

 curds to expel the excessive moisture is never so high as to 

 be fatal to germ life; on the contrary, the acidity of the 



