CHAPTER XVIII. 
SKIMMILK-BUTTERMILK. 
Souring the Skim-milk. As soon as the skim-milk 
leaves the separator, whole milk is added at the rate of 
one gallon to twenty gallons of skim-milk. This gives the 
mixture a fat content, which approximates that of ordinary 
buttermilk. A large quantity of pure culture of lactic 
acid bacteria (starter, see p. 135) is next added and the 
temperature brought to 70° F. Enough starter is added to 
curdle the skim-milk in about six hours at the temperature 
mentioned. This requires about one pound of culture for 
every three pounds of skim-milk. When a temperature 
above 70° F. is employed, there is a tendency for whey 
to separate after the skim-milk has curdled. 
Churning. When thoroughly curdled, the skim-milk 
is placed in a churn and churned for about twenty minutes 
in the same way that cream is churned in making butter. 
The churning process thoroughly breaks up the curd clots, 
resulting in a smooth, thick liquid which cannot be dis- 
tinguished from ordinary good buttermilk. 
Cooling; Immediately after the buttermilk leaves the 
churn, the temperature should be reduced below 50° F. 
to prevent further development of acid and the separa- 
tion of the whey. Ordinary milk and cream coolers with 
enlarged holes in the distributing receptacle will answer 
very satisfactorily. 
Straining. As soon as cooled, the buttermilk should 
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