12 BULLETIN 319, U. S. DEPARTMENT OF AGRICULTURE. 
(3) When these Dottles of milk are cooled, transfer about 1 tea- 
spoonful of milk from each of the bottles of sour milk obtained in 
(1) to one of the bottles of heated and cooled milk. , 
(1) Allow these samples to curdle and repeat the process until one 
sample is obtained which curdles in at least 8 or 10 hours with a 
smooth curd free from whey and gas bubbles and with a pleasant, 
acid taste. 
Gas bubbles, or the separation from the curd of a milky or straw- 
colored whey, show that the lactic-acid bacteria are still mixed with 
other kinds. Considerable variation in flavor can be found in differ- 
ent cultures, and care should be exercised to select one that gives a 
clean and sharp taste. 
(5) Propagate this culture in the same way from day to day. The 
amount of this mother starter which should be carried will depend 
somewhat on the amount of buttermilk to be made. One quart should 
be enough for 20 to 30 gallons. 
(6) (a) Add the mother starter to the milk to be used for butter- 
milk, or (b) pasteurize the milk in a continuous pasteurizer at 180° 
to 185° F. (82° to 85° C), or preferably hold the milk in water- 
jacketed vats or cans at 180° F. (82° C.) for 30 minutes to an hour: 
cool to about 70° F. (21.1° C.) and add the mother starter. The most 
desirable temperature for this fermentation is TO to 75° F. (21.1° to 
21°C). 
(7) \Yhen this milk has curdled, cool it at once to about 50° F. 
and churn thoroughly to break the curd into fine particles. 
The buttermilk should be smooth, free from lumps, and show a 
separation of whey and curd only on long standing. 
Milk to be used for making buttermilk should be fresh and clean 
flavored. Good buttermilk can not be made from milk that is tainted 
or too old to be used for other purposes. Skimmed, partly skimmed. 
or whole milk, as desired, may be used. 
A more nearly uniform product is secured if the milk is pasteur- 
ized. The scorched taste which results from pasteurization at a high 
temperature is not objectionable, as it is obscured by the acidity of 
the soured milk. The time of the inoculation may be arranged to suit 
the convenience of the maker and can be determined by experience in 
each individual case. Using the same culture and holding the tem- 
perature uniform, the amount of the starter can be adjusted to bring 
the acidity to the curdling point at any definite time within narrow 
limits. The temperature of the milk should be between 21° and 21° C. 
(70° and 75° F.). More rapid development of acid can be obtained at 
higher temperatures, but at the lower temperatures the lactic-acid 
bacteria are more successful in checking the growth of digesting and 
gas-forming bacteria. At lower temperatures and with a slower de- 
velopment of acid the casein is precipitated in a finer and more friable 
