602 MILK 



crease the viscosity of the milk materially, to prevent clogging of 

 the machine. 



Although the temperature range for best results is greater for 

 centrifugal separation of cream than for gravity, it should receive 

 proper attention. The milk, if it is not separated immediately 

 after milking, which is impossible except on the farm, should be 

 warmed slowly and without much agitation. The temperature 

 most suitable for separating is about 90 F., and if the milk is 

 heated rapidly the fat is not liable to become soft enough for 

 efficient separation. However, McKay and Larsen found that 

 milk could be heated rapidly to a temperature of 170 F., and 

 that, contrary to earlier beliefs, the butter did not suffer from this 

 heating. 



It is very important that the milk be perfectly sweet for cen- 

 trifugal separation. Sour milk quickly clogs the machine and, at 

 best, separation is imperfect. 



A separator should run smoothly and at a uniform speed if 

 the best results are desired. 



As stated before, butter is most commonly made from sour or 

 "ripened" cream. The ripening process is a very important one, 

 since it not only increases the yield of butter, but conditions the 

 flavor and aroma. Ripening of cream is a process carried on by 

 bacteria. Whether but one type is concerned in it or several is 

 still a matter of controversy, but it is established that a clean 

 cream produces good butter only when the ripening process pro- 

 ceeds normally. Good butter cannot be produced from dirty 

 milk, as this teems with types of micro-organisms that produce 

 taints. 



The ripening of cream is desirable because (1) the fat sepa- 

 rates more readily in sour than in sweet cream, and churning is, 

 therefore, facilitated and the yield increased; (2) sour cream but- 

 ter keeps its aroma and texture for a longer time than does sweet 

 cream butter, and (3) sour cream butter has a richer aroma than 

 sweet cream butter. The best temperature for cream ripening is 

 60 to 70 F. It is true that the lactic acid bacteria grow some- 

 what better at a higher temperature, but undesirable organisms 

 are also favored. At a moderate temperature the lactic acid bac- 

 teria overcome competition of undesirable organisms more read- 

 ily than at higher temperature. 



During the winter months, when cattle are kept closely in 

 stables, undesirable bacteria are more common in cream than in 

 summer, when cattle are outdoors most of the time. Ripening, 

 therefore, proceeds more satisfactorily in summer than in winter. 



It is a well-known fact that in certain localities a high-grade 

 butter is produced, while in others the quality is inferior. This 



