the same should be grown in milk that is as
germ-free as it is possible to secure it. For this purpose sterilize
some fresh skim-milk in a covered can that has previously been well
steamed. This can be done easily by setting cans containing skim-milk in
a vat filled with water and heating the same to 180 deg. F. or above for
one-half hour or more. Steam should not be introduced directly. This
process destroys all but a few of the most resistant spore-bearing
organisms. This will give a cooked flavor to the milk, but will not
affect the cream to which the starter is added. Dairy supply houses are
now introducing the use of starter cans that are specially made for this
purpose.

4. After the heated milk is cooled down to about 70 deg. or 80 deg. F.,
it can be inoculated with the desired culture. Sometimes it is desirable
to "build up" the starter by propagating it first in a smaller volume of
milk, and then after this has developed, adding it to a larger amount.

This method is of particular value where a large amount of starter is
needed for the cream-ripening.

5. After the milk has been inoculated, it should be kept at a
temperature that is suitable for the rapid development of the contained
bacteria, 65 deg.-75 deg. F., which temperature should be kept as uniform
as possible.

This can best be done by setting the covered can in a vat filled with
warm water. The starter cans are often arranged so that temperature can
be controlled by circulating water.

6. The starter should not be too thoroughly curdled when it is needed
for use, but should be well soured and only partially curdled for it is
difficult to break up thoroughly the curd particles if the starter is
completely curdled. If these curd masses are added to ripening cream,
white specks may appear in the butter.

7. The vigor of the starter is in all probability stronger when the milk
is on the point of curdling than it is after the curd has been formed
some time. The continued formation of lactic acid kills many of the
bacteria and thus weakens the fermentative action. It is therefore
highly important that the acidity of the starter should be closely
watched.

8. Do not refrigerate the starter when it has reached the proper stage
of development, as this retards the bacterial growth in the same manner
as cold weather checks the growth of grain. It is preferable to dilute
the starter, if it cannot be used when ready, with sufficient freshly
sterilized sw