WHAT SHOULD THE OVERRUN OF CREAMERY BE? 135 



in creameries is calculated as described previously. The formula 

 is as follows : 



Butter -fat 



X i co = per cent of actual overrun. 



Calculation of Churn-yield. Instead of expressing the 

 increase of butter over that of fat in the percentage overrun, 

 as above, it is often customary among creamerymen to speak 

 of the " churn-yield." For instance, they say that their test was 

 3.90, and their churn-yield was 5, meaning that on the average 

 each 100 pounds of milk contained 3.9 pounds of fat and yielded 

 5 pounds of butter. The churn-yield is always expressed in per- 

 centage, and is obtained by dividing the total pounds of butter 

 obtained by the total pounds of milk from which the butter was 

 made, according to the following formula: 



Pounds of butter 



"ri j r MT~ X ioo = churn-yield. 



Pounds of milk 



In case cream is handled instead of milk, the same may be 

 obtained by substituting " pounds of cream " for " pounds of 

 milk " in the formula. 



What Should the Overrun in a Creamery Be? In discussing 

 this problem we shall take 80 per cent as the legal standard for 

 fat in butter. If every churning of butter were to drop to this 

 standard, but none below it a thing quite impossible of attain- 

 ment if the patrons were credited with all the fat the creamery 

 received, and if there were no mechanical losses, and no fat in the 

 buttermilk, then every 80 pounds of milk-fat received would 

 make ioo pounds of butter; that is, ioo pounds of fat would 

 make 125 pounds of butter, or, the overrun would be 25 per cent. 



The creamery has some gains and some losses which tend to 

 offset each other. 



The gains come mainly from two sources, namely, (i) a small 

 fraction of a pound of cream on some, but not all, of the cans of 

 cream. (2) A small fraction of a per cent of fat on some, but not 

 all, of the cream tested. 



