MILK AND ITS CARE. 189 



butter fat. The centrifugal separator should 

 remove about 98 per cent, of the butter fat in 

 the form of cream. The cream from the sepa- 

 rator, being removed while the milk is sweet, is 

 in the best condition for food or for butter- 

 making purposes. Separators vary in capacity 

 from 150 to 4,000 pounds of milk per hour. 



Problem. — A farmer feeds to liogs 5 gallons (42.5 

 pounds) of skim-niilk daily from June ist to December 

 ist. What will be his loss, supposing that butter aver- 

 aged iS cents pei- pound, and he sells his hogs for $5.00 

 per hundred pounds, if he separated his cream by the 

 gravity process — 



(a) With shallow pans ? 



(/') With cans 20 inches deep? 



(c) If he used the centrifugal separator? 



(d) By which method of separation would he lose 

 most, and how much more than by each of the other 

 two methods ? 



II. Ripening Cream. 



It is a well-known fact that milk which is al- 

 lowed to stand in a warm place for a few hours 

 begins to sour and finally coagulates. This is a 

 process of fermentation, and is due to the 

 growth of an immense number of living organ- 

 isms called bacteria. These bacteria are not in 

 the milk when it leaves the animal body, but 

 gain access from many sources, such as unclean 

 utensils and dust from the air. 



The souring fermentation is undesirable in 

 milk to be used for food, but is a necessary part 



