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 and 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 hsixe 

 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 hquid form will not keep so long, and it is not safe to use 

 them after they are about nine days old. The cultures which 



