196 MODERN METHODS OF TESTING MILK 



5. FINDING THE "OVERRUN" IN BUTTER- 

 MAKING 



The weight of butter produced is greater than the 

 amount of fat in the milk or cream from which the 

 butter is obtained, because butter, in addition to its 

 fat, contains water, salt and curd. Such excess is 

 called the "overrun" and may be readily ascertained 

 by finding the yield of butter for one pound of fat. 

 While some milk-fat is lost in the skim-milk and but- 

 termilk and in handling during butter-making, enough 

 water, salt and curd are added to the fat to make up 

 these losses and something more. The amount of but- 

 ter yield for a pound of fat in milk or cream neces- 

 sarily varies with the variation of losses of fat in skim- 

 milk and in butter-making and the amount of water, 

 salt, etc., retained in the butter. Hence the "overrun" 

 varies. When the operations of skimming milk and 

 butter-making are properly managed, one pound of 

 fat in milk produces about 1.17 (about I 1-6) pounds 

 of butter. Hence, the "overrun" is .17 or one-sixth, 

 (17 per cent). The "overrun" in case of cream aver- 

 ages about .03 higher than in case of milk, according 

 to Hills. 



Rule. To find the "overrun" when the weight 

 of butter made from a given amount of milk or cream 

 and the per cent, of fat in the milk or cream are known, 

 find the number of pounds of fat in the milk or cream 

 by Rule i, and divide the weight of butter by the weight 

 of fat. From the result subtract i. Example: What 

 is the "overrun" in case of milk testing 4 per cent, of 



