46 CANADIAN DAIRYING. 



tion, but coagulates by the addition of an acid or with 

 rennet, while albumen coagulates with heat. 



Sugar gives to milk its sweet taste. The sour- 

 ing of milk is due to a change of milk sugar into 

 lactic acid, through the action of lactic acid bacteria 

 (small plants). 



The ash constituents of milk bear a very close rela- 

 tion to the casein, hence anything which causes a 

 change of the ash, especially the lime compounds, 

 affects the casein. The pasteurization of milk destroys 

 its usefulness for cheesemaking by changing its 

 mineral matter, and rennet will not act properly on 

 the casein unless the milk be treated with a soluble 

 lime-salt, such as calcium chloride. 



The yellow color of milk is due to special coloring 

 matter known as lactochrome, which is associated 

 with the milk fat. The character and breed of the 

 cow, as well as the food fed to the cow, affect the color 

 of milk. Tests based on the color of milk are not 

 reliable. 



The opacity of milk is due to the fat globules and 

 to- the casein. Fat in the form of small globules will 

 retard more light than will the large ones. This fact, 

 together with the fact that the casein is not all in 

 solution, renders optical milk tests of very little use. 



The odor of milk is due to a volatile oil, which is 

 more pronounced in some samples than in others. 



Gases, composed of air, carbonic acid, ammonia, 

 oxygen, and nitrogen are found in milk, especially 

 soon after milking, hence samples for testing should 

 not be taken within an hour after milking, or the 

 results will be too low. 



