108 BUTTER-MAKING. 



The amount of overrun depends upon: 



1. Thoroughness of skimming. 



2. Completeness of churning. 



3. General losses in the creamery. 



4. Composition of the butter manufactured. 



The theoretical overrun, however, may be quite accurately 

 calculated from the composition of the butter manufactured 

 in a well regulated creamery. In creameries where the con- 

 ditions of separation and churning are almost perfect, the 

 amount of fat lost in the buttermilk and the skimmed milk 

 is quite constant from day to day, and should not exceed .1% 

 in the skimmed milk and .2% in the buttermilk, according 

 to the Babcock test. Basing the calculations upon the above 

 figures, the theoretical overrun may be calculated from the 

 composition of the butter as follows: 



If, for instance, we start with 1000 pounds of milk-testing 

 4' Q fat, there will be a total of 40 pounds of fat. If we skim 

 32% cream from 4% milk, we should have -^j, or |^, of it cream, 

 and the remainder skim-milk, or 125 pounds of cream and 

 875 pounds of skimmed milk. If there were .1% of fat in the 

 skimmed milk, there Avould be a loss of .875 pounds of fat during 

 skimming. There would then be 39.125 pounds of fat in the 

 125 pounds of cream (40 -.875 = 39. 125). If 10% of starter 

 were added to the cream we should get 137.5 pounds of cream 

 testing 28.4%. (125 pounds creamXl.lO= 137.5 pounds cream; 

 39.125-^137.5 = 28.4% fat.) By churning this cream we 

 should obtain about 100 pounds of buttermilk. If it tested 

 .2% fat there would be a loss of about .2 pounds of fat, making 

 a total loss of fat in skim-milk and buttermilk of 1.075 pounds. 

 Subtracting this total loss of 1.075 from 40 pounds we would 

 have 38.925 pounds of fat left to be made into butter 

 (40-1.075 = 38.925 pounds of fat). If the butter on analysis 

 proves to contain 82% fat, the total number of pounds manu- 

 factured will be 38.925-^82 = 47.47 pounds of butter. 47.47- 

 40 = 7.47 pounds theoretical overrun, and 7.47^40X100=18.7% 

 overrun (theoretical). 



