CALCULATTOX OF 0\'ERRUX 133 



It is very common for creamery patrons to test the milk 

 from each of their cows, then add the tests together and di\'ide 

 by the total number of cows tested. The result they will 

 call the average test, and frequently such tests are made use of 

 as evidence against a creamery operator to pro^•e that his tests 

 at the creamery were not correct. The fallacy is evident from 

 what has been said above. 



The same mistake is also likely to be made in finding the aver- 

 age test from several creamery-plants and skimming-statinns. 



Calculation of Overrun. — The amount of overrun is the dif- 

 ference between the amount of pure butter-fat and the amount 

 of butter manufactured from that gi\X'n amount of fat. This 

 difference, divided by the amount of fat and multiplied by loo 

 will give the percentage of overrun. The calculation of the 

 overrun in the creamery should alwa}'s be made from the fat- 

 basis on which the patrons are being paid. If the fat is delivered 

 in tire cream, the overrun should be calculated from the fat in 

 the cream. The overrun calculated from the composition of the 

 butter manufactured would not be an indication of the correct 

 overrun, as there might be serious losses of fat sustained during 

 the different steps in the manufacture, such as from inefficient 

 skimming, incomplete churning, and general losses in the cream- 

 cry. It is possible that butter might show a high content of the 

 substances not fat, and }-et not show a good overrun on account 

 of losses; while butter containing only a medium high mijislure- 

 content might show as great or greater overrun on account of 

 thorough and efficient work during the different steps of manu- 

 facture. 

 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 condi- 

 tions of separation and churning are almost perfect, the amount 



