12 
Colorado Experiment Station 
ized ahead. If the three day sterilization is employed, the bottles 
should be kept in a warm room between each sterilization to hasten 
the development of the spores into the vegetative forms, which are 
more easily killed by heat. If the one day sterilization is adopted, 
all the more care must be taken in selecting clean milk since the 
fewer the bacteria present, the more efficient will be the sterilization. 
Add the entire contents of the bottle of culture obtained from 
the manufacturer to one of the bottles of sterile milk and shake it 
gently for about five minutes so as to distribute the culture uniformly 
through the milk. Allow it to develop at a temperature of 75 degrees 
to 85 degrees F. The milk will become soured and curdled into a 
solid mass in from 18 to 24 hours and in this condition is known 
as the “Mother Starter/’ It is now ready for use in building up the 
starter proper, to be employed in ripening the cream. But before 
taking this step, a small portion of it should be transferred to a 
second bottle of sterile milk either with the teaspoon provided or 
by simply carrying over the cotton swab to the new bottle and al¬ 
lowing it to remain there for use the next day. In this way a sec¬ 
ond mother starter is prepared for the following day. In making 
the transfers from one bottle to another, the bottles should be left 
open to the air only long enough to make the transfer and then 
closed at once. If this precaution is not taken, there is great danger 
of contamination by air bacteria which would result, probably, in the 
starter going “off flavor." New mother starters should be prepared 
in this -way every day whether they are to be used or not, since the 
activity of the lactic acid bacteria decreases rather rapidly if this is 
not done. 
A good mother starter should appear smooth, glistening, firm 
and free from gas holes or free whey. It is always desirable to ex¬ 
amine the ripened starter for flavor, odor, and acidity. This should be 
done by pouring a small quantity from the bottle into a clean cup, 
rather than by dipping any utensil into it which might be the means 
of introducing undesirable germs. The starter should have a clean 
taste, that is, it should be free from any disagreeable flavors; it should 
have a pleasant odor and should be only slightly acid. 
Preparation of the Starter Proper. 
The milk for this purpose should be selected for its purity and 
must be pasteurized by heating it for thirty to forty-five minutes at 
a temperature of 150 degrees to 160 degrees F. Cool this milk to 75 
degrees to 85 degrees F. before adding the mother starter. 
To forty or fifty parts of pasteurized whole or skimmed milk, 
add one part of mother starter. Let this stand for 18 to 24 hours 
at room temperature, 68 degrees to 70 degrees F., when it will be 
curdled; stir it thoroughly and it is ready to be added to the cream 
as a starter. The starter should be used at the time it contains the 
greatest number of active organisms. ’If too much acid is developed, 
the bacteria are killed, and to this fact is due the bad effects of over 
