DAIRYING 47 



milk without heating it. A temperature above 75 degrees F. may 

 not do any harm, but the best separators will skim summer milk 

 at. a temperature of 75 degrees and leave only one-tenth of one 

 per cent, or less of fat in the skim milk. In the fall and winter 

 seasons when the cows are drying up, the milk should be heated 

 to 80 or 85 degrees F. for separating. If the temperature falls 

 below 70 degrees F. and in some cases below 80 degrees F., there 

 may be an unnecessarily large loss of butter fat in the skim milk 

 as a great fluctuation in the temperature during separation is detri- 

 mental to the best skimming. The higher the temperature of the 

 milk, the better the skimming, and it has been suggested that by 

 heating milk to 160 degrees F., or to a pasteurizing temperature, 

 that nearly all the fat in the milk may be skimmed out. Such a 

 high temperature will undoubtedly aid in removing the last traces 

 of fat from the skim milk, but the uniform heating to 80 degrees 

 F. is the temperature commonly recommended and used. 



305. The temperature of the milk changes its viscosity and 

 this influences the separation of the fat globules ; the warmer 

 the milk the thinner the serum, and the colder the milk the 

 thicker the serum becomes. There is not much increase in 

 efficiency of skimming- when the temperature of the milk goes 

 above 90 degrees F. A higher temperature than this does not 

 give enough better skimming to pay for the extra heat. Skim- 

 ming milk at a pasteurizing temperature, 160 degrees F., in- 

 creases the capacity of the separator and more slime is thrown 

 out of hot milk than when skimmed at 85 degrees F. 



306. When first drawn from the cow, milk skims better than 

 after standing several hours. This may be due to the solidifying 

 of the fat globules, to the enclosing of these globules in the curd 

 or casein to some extent, and to changes in the casein which make 

 the milk more viscous. 



307. A change in the viscosity or fluid condition of the milk 

 las been noticed when cows change from stable to pasture feed, 

 ind again when they return from pasture to stable feed in the 

 fall. The following figures* illustrate this change in the skim- 

 efficiency : 



*Kirchner Milchwirtschaft. 



