202 BACTERIA IN BUTTER AND OLEOMARGARINE 
all. With this change our butter-makers were willing to try 
pure cultures and in a short time American butter-makers learned 
of their meaning and began to experiment with them widely. 
The result of the dozen or so years of experience has been to show 
the extreme value of starters as a means of controlling the ripen- 
ing, until to-day starters of some kind are almost universally 
used in all good creameries and dairies. 
Preparation of Starters.—While starters are very widely 
used to-day, they are not always pure cultures. Two quite dif- 
ferent methods of preparing them are in use. 
Natural Siarters —A natural starter is nothing more than some 
normally soured milk. In order to obtain it it is only necessary 
to select several quarts of good milk and place it in a clean, steril- 
ized pail or can, covered to keep out the dust, and keep it in a 
temperature 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 ex- 
perience is needed on the part of the butter-maker to know 
whether the starter is satisfactory. 
Starters from Commercial Culiures-—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 some- 
times 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: 
