FIRST STEPS IN CHEESE-MAKING 19 



preparing a starter for the following day, putting a 

 little into some skim-milk that has been heated to 180 

 F. for 30 minutes, cooled to 70 F., and then allowed 

 to stand 18 to 24 hours. The starter may thus be 

 propagated from day to day. Occasionally, almost 

 pure cultures of lactic acid bacteria can be obtained 

 in this way, but this is an exceptional experience. 

 Results much more reliable come from the use of 

 commercial starters. (2) Commercial starters. Com- 

 mercial starters are special preparations consisting of 

 certain organisms that produce lactic acid. These are 

 carefully prepared under the supervision of trained 

 bacteriologists and sold to cheese-makers. They are 

 usually known as cultures or pure cultures. The 

 medium in which these organisms are sent out may 

 . be milk, broths, milk-sugar or porous paper. Proper 

 directions, with necessary precautions, usually ac- 

 company these commercial preparations. Below is 

 given a satisfactory method for the use of a com- 

 mercial preparation in making a starter for cheese- 

 making. 



Inoculation of the culture. In a can or glass ves- 

 sel that has been thoroughly cleaned and sterilized 

 with boiling water,. place one quart of clean, sweet 

 milk. Heat the milk to at least 185 F. for one hour 

 by placing the can or vessel in boiling water. At the 

 end of an hour cool the milk rapidly to 95 F. by 

 setting the can or vessel in cold water. Then add the 

 contents of the small bottle of a prepared culture to 

 the milk, stirring it in with a sterilized spoon. Allow 

 the milk to cool gradually to 70 F. and hold at this 

 temperature for 24 hours. At the end of this time 

 the milk should be sour and coagulated. 



