12 DAIRYING 



bottle is then two-thirds filled with clean, sweet, fresh, whole 

 milk and two or more of these bottles are placed in the gal- 

 vanized iron can, or sterilizer. Steam or hot water is then 

 turned into the can carefully, so as not to break the bottles, and 

 the heat gradually raised to about 180 degrees Fahrenheit, which 

 temperature is held for at least 15 minutes. The entire heating 

 process may take one-half hour. This heating kills all the bac- 

 teria in the milk, except some spores, and provides a nearly 

 germ-free soil in which to develop the pure culture. The bottles 

 of milk are allowed to cool without removing the glass tumblers 

 used as a cover; when cool they may be used as needed for 

 building up a starter. 



Adding the Pure Culture. 



536. When small bottles or packages of pure culture of bac- 

 teria are bought for starter-making, the cork or wrappings should 

 be carefully removed, in order to prevent any outside contami- 

 nation. All the liquid, or the powder, should be added to one 

 of the bottles of sterile milk previously prepared. (See par. 535.) 

 The glass tumbler cover is then placed on the bottle and the 

 contents mixed by occasional shaking. It is then placed in the 

 incubator and a pail of water added to the box, so as to bring 

 the temperature up to about 80 or 90 degrees Fahrenheit. At 

 this temperature the pure culture bacteria will soon begin to 

 grow and the sterile milk in the bottle will coagulate in a few 

 hours. It is then rilled with millions of the bacteria needed for 

 making the starter, and after transferring a spoonful of the 

 coagulated milk from this bottle to another bottle of sterile milk, 

 which is then put in the incubator for the next day, the con- 

 tents of the first bottle is added to a larger quantity of pasteur- 

 ized skim milk. This is then thoroughly mixed and when the 

 laiger amount has been held at a temperature of about 80 de- 

 grees Fahrenheit for a long enough time to coagulate it. this 

 sour milk is added to the cream, which is to be ripened. 



537. By this process there is added to the cream many 

 millions of bacteria like those in the pure culture bought. The 



