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 
