402 THIS OVERRUN 



taken and kept in tightly sealed jars, and if they cannot be tested 

 promptly, they should be placed in the cold room until needed. 



Mechanical Losses of Fat. Of the mechanical losses of fat 

 in the creamery which materially affect the overrun, the fat 

 lost in the skim milk and the fat lost in the buttermilk are the 

 most important. 



Skim Milk. On the basis of average milk, testing about 4 

 per cent fat and of butter containing 80 per cent fat, every one- 

 tenth per cent fat lost in the skim milk reduces the overrun by 

 about 2.2 per cent. It is obvious, therefore, that whole milk cream- 

 eries cannot hope to secure as large an overrun as gathered cream 

 creameries. The very marked effect of the small amount of fat 

 lost in the skim milk, on the overrun, emphasizes the importance 

 of securing the greatest possible skimming efficiency in the 

 operation of the factory cream separator, so as to reduce the 

 resulting loss to the very minimum. For detailed directions on 

 the factors which influence the skimming efficiency of the cream 

 separator the reader is referred to Chapter V on the "Separation 

 of Milk." 



Buttermilk. The exhaustiveness of the churning does not 

 have so great an effect on the overrun as does the exhaustive- 

 ness of skimming, yet it is a factor that must be reckoned with 

 in order to secure maximum overrun. With cream testing about 

 33 per cent fat and using 10 per cent starter, and with butter 

 containing 80 per cent fat, each one-tenth per cent fat lost in 

 the buttermilk lowers the overrun approximately .23 per cent. 

 It is generally considered that an average buttermilk test of not 

 to exceed .2 per cent fat is not excessive on this basis ; the 

 sacrifice in overrun that may be expected under fairly normal 

 conditions, due to the fat lost in the buttermilk, is about .5 

 per cent. 



In a properly operated creamery where the conditions relat- 

 ing to exhaustiveness of churning are carefully watched, the but- 

 termilk seldom exceeds .2 per cent, and frequently drops below 

 .1 per cent. In plants which ignore the importance of the ex- 

 haustiveness of churning and which do not systematically check 

 it up by testing the buttermilk, it is not uncommon to find the 



