MICRO-ORGANISMS AND ENZYMS 



The lactic acid fermentation we have been con- 

 sidering is what we may call the normal form, the 

 particular form we desire to have present in milk in 

 cheese-making. Their presence is insured by the use 

 of good starters (p. 18). Milk in which this form 

 of lactic fermentation has occurred produces, in 

 souring, a firm curd free from gas bubbles and with 

 only a little whey on the surface. When agitated, 

 the curd breaks apart readily into small particles, 

 which settle slowly and leave a clear whey. The 

 milk should have a pleasant, clean, acid taste, en- 

 tirely free from anything resembling a tainted flavor. 

 So far as we know, the lactic acid bacteria belonging 

 to this normal group never form products of a poison- 

 ous character. 



GAS-PRODUCING BACTERIA 



Some of the bacteria that decompose milk-sugar 

 with formation of lactic acid are usually grouped with 

 the lactic acid bacteria, though they possess distinguish- 

 ing characteristics which mark them as abnormal, so 

 far as their behavior in cheese-making is concerned. 

 While they decompose milk-sugar and produce lactic 

 acid, they produce other products besides, especially 

 gases; they may also produce volatile products that 

 are offensive. These bacteria are responsible for many 

 of the defects in cheese (pp. 116-130). When gas- 

 producing ferments are present in milk, they are 

 usually responsible for increased losses of fat in the 

 cheese-making process. 



DIGESTING BACTERIA 



A large group of bacteria curdle milk without sour- 

 ing it and then slowly digest or dissolve the curd; 



