246 Milk and Its Products 
required for the ripening will be shortened, and more 
uniform results be obtained if, in addition to the 
warming, an artificial starter is used. This may be 
any material containing the germs of lactic fermen- 
tation in active condition. The whey saved from 
the previous day, or milk naturally or artificially 
soured, may be used. An _ extremely convenient 
form of starter is made by preparing an artificial 
ferment in the following way: Ten pounds of 
whole milk are sterilized at 180° F., then cooled to 
90°, and sufficient commercial dry lactic ferment 
added to secure coagulation in twenty-four hours. 
When coagulated, this is added to the extent. of 10 
per cent to enough whole milk to make sufficient 
starter for one day’s use. (See Appendix A.) The 
amount of starter to be added for the purpose of 
ripening the milk should be from 2 to 5 per cent, 
varying with the temperature of the air and the 
amount of ripeness that it is necessary to develop after 
the milk reaches the factory. Enough of the ferment 
should be reserved each day to prepare ferment for 
the following day from whole milk; and with eare that 
the vessels in which the ferment is made are kept 
clean and sweet, a single ferment may be propagated 
for from ten days to two weeks. As a matter of fact, 
there is no reason why a ferment may not be propa- 
gated for an indefinite time. All that is necessary is to 
keep everything bacteriologically clean and to prevent 
infection by never allowing any dust or solid particles 
to fall into the ferment and never to touch it with the 
hands. Such a ferment will give more uniform results, 
