2 DAIRY TECHNOLOGY 



left exposed to the air. The flavor of milk is slightly sweet- 

 ish. Fresh milk has an amphoteric reaction, turns red 

 litmus paper blue and blue litmus paper red. This re- 

 action, so far as known, is due to the presence of phosphates 

 in the milk. Fresh milk, however, appears acid to phenol- 

 phthalein, and when titrated with tenth-normal alkali 

 shows an apparent acidity of from o.io to 0.14 per cent. 

 This acidity is undoubtedly due to the presence in the 

 milk of phosphates, citrates, casein and carbon dioxide. 



The viscosity of milk is greater than that of water. It 

 is increased by age, low temperature, products of fermen- 

 tation and a high solid and fat content. The viscosity 

 of milk is decreased by high temperature, a low solid and 

 fat content and certain fermentations. 



Milk possesses a certain adhesive property. It sticks 

 to wood, glass and metals to a greater degree than does 

 water. A paper moistened with milk or cream makes a 

 label that will stick to any dry object. A similar paper 

 moistened with skimmed milk has less adhesive power. 

 The adhesive property of milk is in part dependent upon 

 the nitrogenous matter. This fact is made use of in paint- 

 ing and whitewashing. The addition of milk causes the 

 paint to adhere better. When milk is allowed to stand at 

 room temperature, it undergoes fermentation; lactic acid 

 is formed and the milk becomes thick and curdled. The 

 curdling of milk may be produced by the addition of any 

 dilute acid. If the milk thus curdled is neutralized with an 

 alkali, such as lime water, ammonia or potash, the curd is 

 redissolved. Milk may also be curdled by rennet or pepsin, 

 and the curd thus produced cannot so easily be redissolved 

 by weak alkali solutions. 



Milk is slightly heavier than water; its specific gravity 

 varies from 1.029 to 1.034 at 60 F. 



