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% fat, there will be a total of 40 pounds of fat. If we skim 
32% cream from 4% milk, we should have +5, or 4, 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 would 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 cream x 1.10= 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 +40 x 100= 18.7% 
overrun (theoretical). 
