BACTERIA IN BUTTER-MAKING 203 
A quart of skim milk, whole milk, or cream is placed in a glass 
jar and sterilized, either by boiling or, better, by pasteurizing at 
180° for half an hour, stirring frequently to insure uniform heating. 
The milk is then cooled, and when it has reached a temperature of 
80° the commercial culture, from a freshly opened package, is 
thoroughly stirred in; the whole is covered to keep out the dust and 
placed at a temperature of about 65°. When the milk has become 
quite sour, but before it is curdled, it is ready to use as a starter. 
If a larger amount of starter is needed, this first starter is placed in 
a large can of pasteurized milk and allowed to grow in it at 65° 
until the whole becomes soured. By this means any desired 
amount can be prepared. 
The starter thus prepared is added to the cream in varying 
proportions, the larger the amount the quicker the ripening. 
Sometimes one part of the starter to ten parts of cream is used; in 
other cases a smaller amount is used and sometimes more. After 
the ripened cream is ready to churn, a certain quantity of itis 
removed, placed in a clean can, and set aside to serve as a starter 
for the next day’s churning. In this way some starter is reserved 
each day, to be used in the cream collected that day; and thus the 
original starter is carried on from churning to churning. After 
some days, however, it is necessary to resort once more to a pure 
culture, built up in the same way. 
There is not very much to choose between natural starters and 
commercial cultures. Natural starters cost nothing except the 
trouble of making them, but, on the other hand, they are not 
uniform, and not always to be depended upon. Commercial cul- 
tures cost a small sum, but they are rather more uniform than 
natural starters. It has been claimed that the flavor of butter 
from cream ripened with a natural starter is higher than that 
ripened with a pure culture. This is easy to understand. A good 
starter should sour cream promptly; should thrive at 60° to 72°; 
should coagulate milk and cream into a homogeneous mixture, 
and should produce an agreeable aromatic taste. No single bac- 
