1 88 BACTERIA IN BUTTER AND OLEOMARGARINE. 
of from 65 to 70. After one or two days the milk should show 
signs of souring; when it has become decidedly sour, but not yet 
curdled, it is to be used as a starter. It requires some skill on the 
part of the butter-maker to know whether the starter thus obtained 
is of the best character and whether it should be used or thrown 
away and another obtained. Starters made in this way are not 
sure to be uniform, inasmuch as the different samples of milk may 
contain different types of bacteria, and experience is needed on the 
part of the butter-maker to know whether the starter is satisfactory. 
Starters from Commercial Cultures. Commercial starters are 
now a well-known article, and several different brands may be pur- 
chased. In all cases they are prepared by bacteriologists and 
consist of a culture of bacteria usually a pure culture, though not 
always that have been found by experiment to produce favorable 
results in the ripening. These starters as purchased are sometimes 
in the form of a powder, sometimes in the form of a liquid, but in 
all cases contain too small a quantity to add directly to the cream 
that is to be ripened. The quantity of -bacteria must, therefore, 
be increased before using by a process called building up. The 
procedure is as follows: 
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 
1 80 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 & freshly opened package, is thor- 
oughly 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. Some- 
times 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 
