44 BULLETIN 973, U. S. DEPARTMENT OF AGRICULTURE. 
MANUFACTURE OF BY-PRODUCTS. 
A milk-plant operator should be familiar with the manufacture of 
the ordinary by-products. 
COTTAGE CHEESE. 
For directions on the manufacture of cottage cheese, reference is 
made to United States Department of Agriculture Bulletin No. 576, 
"The Manufacture of Cottage Cheese in Creameries and Milk Plants." 
BUTTERMILK AND ARTIFICIAL BUTTERMILK. 
One of the most economical ways of disposing of surplus milk is 
by the sale of buttermilk or of artificial buttermilk. Skim milk or 
sour milk can be utilized profitably in this way. It takes practice 
and experience to be able to obtain a uniformly good product, but the 
following notes may be of assistance to those not familiar with the 
process : 
Clean, sweet skim milk or whole milk should be used, and pasteuriza- 
tion is preferable, as it insures a better product from both a commer- 
cial and a sanitary standpoint. If skim milk is used better results 
are obtained if some whole milk is mixed with it, as 1 part whole 
milk to 3 parts skim milk. Run the milk after pasteurizing into a 
water-jacketed vat, and add good, clean starter enough to ripen the 
milk by the time wanted for churning. From 5 to 10 gallons of 
starter for each 100 gallons of milk should be sufficient. Take 
particular care to keep a good starter on hand, renewing it as often 
as necessary. Cover the vat to keep out flies and dirt, and ripen 
the milk at a temperature of from 60° to 70° F. The ripening 
temperature depends upon the amount of starter added and the 
length of time which the milk has to stand. Ripen the milk until 
it is coagulated into a rather soft curd. If the milk ripens too 
rapidly, run cold water around the vat to check the process. When 
the milk is ready, strain it into the churn, and churn for about 20 
minutes, or until the butter has gathered in small granules. The 
milk should be churned at between 55° and 65° F. When butter 
comes, strain the buttermilk and cool it at once, using a cooler if 
possible. If no cooler is available, put the cans immediately into 
a tank of ice water or a refrigerator. If possible, bottle the retail 
buttermilk at once. Whenever possible, use a separate bottler for 
buttermilk. If not possible, particular care should be taken in wash- 
ing and sterilizing the machine after buttermilk has been handled. 
Further information on this subject is given in United States 
Department of Agriculture Bulletin No. 319, " Fermented Milks," 
which may be obtained from the Superintendent of Documents, 
Government Printing Office, for 5 cents; stamps not accepted. 
WEIGHTS OF MILK AND CREAM. 
In general the specific gravity of milk and cream depends on the 
percentage and relation of the solids, the temperature at which the 
determinations ure made, and the age of the milk. The weight of 
1 gallon of water at 68° F. (20° C.) according to the Bureau of 
Standards is 8.32162 pounds. Using this figure as the weight of 
