198 Milk and Its Products 



ance of such flavors, and it is by no means certain 

 that the flavors are not in part produced as the result 

 of direct oxidation. It is found in practice that the 

 regulation of the production of lactic acid is the 

 chief means in controlling the flavor. 



The means of producing lactic acid. In order that 

 the milk or cream should ripen, or become sour, it 

 is necessary that germs of lactic acid fermentations 

 should gain access to it, and that a temperature favor- 

 able to their normal development should be secured. 

 The presence of the germs may be left to chance 

 inoculation, or they may be artificially supplied. 

 Under ordinary conditions, "by the time the cream has 

 been separated from the milk, there will have reached 

 it a sufficient number of germs of fermentation to 

 cause a rapid production of lactic acid, though the 

 number will vary from day to day and from time to 

 time, and a certain amount of acid cannot be de- 

 pended upon within any given specified time. The 

 inoculation is more certain, and the desired degree 

 of acidity will be more surely reached, at the end 

 of a given time, if the germs are added in suffi- 

 cient quantity artificially. The source of the inocu- 

 lation may be buttermilk or cream from preceding 

 churnings, or it may be in the form of an artificially 

 prepared "starter" of sour skimmed milk, or it may 

 be in the form of any of the so-called commercial 

 lactic ferments. It is desirable that none but the 

 proper germs should find access to the milk, and 

 in relying upon natural means there is always more 

 or less danger that putrefactive and other undesirable 



