74 MANUAL OF MILK PRODUCTS 



that if a vessel will hold just 100 lb. of water at the tempera- 

 ture of 60° F., it will hold 103.2 lb. of milk of average composi- 

 tion. The weight of the milk divided by that of the water 

 gives 1.032 as the specific gravity of the milk. Since there is 

 considerable variation in the solids in milk, it follows that the 

 specific gravity will also vary ; the limits of variation for normal 

 milks usually being between 1.029 and 1.035 at 60° F. Skim 

 milk has a specific gravity of about 1.036—1.038 and milk-fat 

 about 0.900. An increase in fat relative to the other solids, 

 therefore, lowers the specific gravity of milk, while its removal 

 raises the specific gravity. The same is true of the water-con- 

 tent in relation to the solids. Since the volume of liquids is 

 affected- by temperature, this fact must be taken into account 

 in determining the specific gravity of milk. As the tempera- 

 ture is raised, the volume of the milk is increased and the specific 

 gravity lowered, while the opposite is true when the temperature 

 is lowered. It is, therefore, necessary to use a standard tem- 

 perature when determining the specific gravity of milk. The 

 temperature of 60° F. is generally used for this purpose. 



ODOR OF MILK 



As milk is drawn from the udder, it has a characteristic sweet- 

 ish, pleasant odor. This is probably largely due to the gases 

 which it contains. Normally the odor of fresh milk is not very 

 pronounced and decreases rapidly when exposed to pure air or 

 cooled. The odor varies with the milk of individual cows, 

 perhaps being influenced by the physical condition of the animal. 

 Milk absorbs foreign odors very quickly. These may come 

 from the feeds eaten by the cows before milking or from odors 

 in the atmosphere to which it is exposed after it is drawn from 

 the cow. These odors become less pronounced as the milk 

 increases in age. 



