490 MANUAL OF MILK PRODUCTS 



to lactic acid the buttermilk may contain in small quantities 

 acetic, succinic, and formic acids, and sometimes traces of 

 alcohol. The lactic bacteria form lactic acid, with only slight 

 traces of other organic acids, no alcohol, and no gas. In well- 

 managed creameries the acid fermentation is assisted and con- 

 trolled to some extent by the use of a starter. This may be 

 milk allowed to sour spontaneously, or buttermilk from the 

 previous day's churning, but careful butter-makers build up 

 starters from commercial cultures sold in the form of powders, 

 tablets, or fluid cultures, as varieties of lactic acid bacteria 

 selected with special reference to the production of a desirable 

 flavor in butter. The butter-maker puts this culture into 

 about a quart of milk which has been steamed for an hour or 

 more to reduce the bacteria to the lowest possible number. 

 After standing overnight the milk will usually be curdled, but 

 gas bubbles and other evidences of contamination may be 

 observed. A small portion of this milk is transferred to an- 

 other bottle of milk prepared as before, and this process is 

 continued until the acid fermentation has become sufficiently 

 active to eliminate the contaminating bacteria, and the milk 

 curdles with a clean, acid taste and without signs of gas or 

 "wheying off." This small starter, or "mother starter/' is 

 carried along indefinitely by daily transfers to freshly steamed 

 milk. If reasonable precautions are taken to prevent con- 

 tamination after a thorough heating of the milk, this culture 

 will remain pure and vigorous for an indefinite time. 



To prepare the starter actually used in ripening the cream, 

 a larger lot of milk — 25 to 50 gallons or more, according to 

 the amount of cream — is heated for an hour or more. This 

 is usually done in a special apparatus (sold by creamery supply 

 houses) which consists of a large can inclosed on the sides and 

 bottom by a steam jacket and fitted with a belt-driven stirrer. 

 Milk either skimmed or unskimmed is heated by turning steam 

 into the jacket; during the heating the milk is stirred con- 



