Calculation of Butter- and Cheese Yield. 189 



214. "Overrun" of churn over test. The yield of 

 butter is not, however, as a rule compared with the 

 amount of butter fat contained in the butter, but with 

 the total butter fat of the, whole milk or cream from 

 which it was made. This "increase of the churn over 

 the test" is what is generally called overrun in cream- 

 eries. 



The overrun obtained in different creameries, or even 

 in the same creameries at different times, will be found 

 to vary considerably. When the milk is accurately 

 tested and the butter well worked, this overrun will vary 

 from 10 to 16 per cent. ; that is, if a quantity of milk 

 contains exactly 100 Ibs of butter fat, as found by the 

 Babcock test or any other accurate method of milk test- 

 ing, from 110 to 116 Ibs. of butter ready for market may 

 be obtained from it. The overrun from cream will be 

 somewhat larger, 18 to 22 per cent., but will never ex- 

 ceed 25 per cent., unless the butter contains less than 

 80 per cent, fat (217). 



215. Factors influencing the overrun from milk. 

 Even under the very best of care and attention to de- 

 tails, variations will occur in the speed of the separator, 

 in the conduct of the ripening and churning processes, 

 and in the condition of the butter when the churn is 

 stopped ; hence absolutely uniform losses of fat in skim 

 milk and butter milk, or the same water- and salt con- 

 tents of the butter, cannot be expected. 



The overrun in separator creameries is influenced by 

 two legitimate factors : first, the losses of butter fat sus- 

 tained in separating the milk and churning the cream, 

 and second, the gain due to the admixture of water, 



