n.

In order to accomplish this, the maker must be able to maintain
constant conditions from day to day, especially with reference to
the amount of the ripened starter that is transferred to the fresh
bottle of milk, and the temperature at which the bottles are kept. A
spoon, arranged as shown in Fig. 31, enables one to carry a definite
amount of the ripened starter to the bottle of milk to be inoculated
and a constant temperature box (Fig. 32) permits of the maintenance
of the same temperature from day to day. Through careful supervision
of these points, and by taking care at every step to avoid the
introduction of contaminating organisms, the purity of the culture
can be maintained, and the bacteria kept in a healthy condition.

The starter is used because of the acid-forming bacteria it
contains; it is said to be ripe and in the best condition for use at
the time it contains the greatest number of living bacteria. It
has been found by experiment that this is at the time the milk
curdles at ordinary temperature, or when the acidity is about
0.6-0.7 per cent. If the acidity is allowed to increase to 0.8 or
0.9 per cent, the number of bacteria will be less and a larger
amount of the starter must be used in order to ripen a definite
amount of cream in the desired time. The use of an overripe starter
may also have an injurious effect on the flavor.

[Illustration: Fig. 31.--Bottle for Mother Starters.

A milk bottle with a tumbler for a cover and a spoon for inoculating
the other bottles enables the butter maker to propagate the starters
without contamination.]

The ripened starter should be perfectly homogeneous, showing no
bubbles of gas or free whey; the odor should be agreeable and the
acid taste mild; on shaking, the curd should break up into a smooth,
creamy liquid free from lumps. This is especially important in the
starter that is to be added to the cream, since otherwise the
starter cannot be uniformly mixed with it and white specks of
curdled casein will be noted in the butter.

[Illustration: Fig. 32.--An Incubating Chamber for Starters.

The inner compartment will hold a pail of water and the bottles for
the mother starters. The temperature can be kept at any desired
point by the use of warm or cold water. The four-inch space between
the walls is filled with hay or mineral wool.]

The firmness of the curd is not so dependent on the amount of acid
formed as upon other factors. If the curd shrinks to a