STARTERS. 217 
are supposed to contain a preponderance of those germs which 
are involved in the production of desirable flavors in butter. 
Buttermilk, sour cream, whey, and sour whole or skim-milk, 
are classed under this heading. While all these may be termed 
natural starters, and at certain times the use of any one of 
them may produce better results than if no starter at all were 
used, it is not safe to rely upon these to bring about better 
results than could be obtained without the use of starters, 
because these products are likely to be contaminated in a large 
degree with undesirable germs. 
Preparation of Natural Starters—-The best natural starter 
is usually obtained by selecting a number of different samples 
of the best milk coming into the creamery, into cleaned sterile 
glass jars. The samples are allowed to stand until sour at 
about 70° F. The sample which coagulates into a smooth uni- 
form curd, and has a pleasant acid taste and smell is selected 
and used as a mother-starter. When inoculated into a large 
quantity of selected pasteurized skim-milk, cooled to ard kept 
at a temperature of about 70° F. until it begins to coagulate, 
it will usually produce a starter which is equal, and often 
superior, to a commercial starter. 
Commercial Starters, or Pure Cultures.—Experiments have 
amply proved that certain species of bacteria are chiefly re- 
sponsible for the butter flavors developed in cream during 
ripening. This fact has given rise to the use of pure cultures 
prepared in a commercial way. These pure cultures contain, 
in a virulent condition, the germs which produce the desirable 
flavors and aroma. The cultures are put up in laboratories 
specially provided for this kind of work. The germs are iso- 
lated and inoculated into a medium which is suitable to their 
growth. Some laboratories inoculate them into a liquid medium, 
others into a powder medium. The liquid medium consists 
usually of sterilized bouillon, or milk. The powder medium 
consists chiefly of milk-sugar. The cultures that are put up 
in the liquid form will not keep so long, and it is not safe to use 
them after they are about nine days old. The cultures which 
