58 MILK [v 



reagents, such as dilute acids, salts, alcohol, etc., and 

 by rennet. It is worthy of note that the coagulation, 

 which is formed by spontaneous souring of milk, 

 and that formed by different coagulating reagents, 

 differ in their nature a point which will be discussed 

 in a subsequent Chapter. 



Effect of Heat. The extent to which coagula- 

 tion of the casein in milk takes place and the 

 relative effect of different coagulating reagents is 

 influenced by temperature and certain other con- 

 ditions. Thus the higher the temperature (up to 

 boiling-point), the less the quantity of acids or other 

 precipitating reagents required to effect coagulation. 

 Again, coagulation seems to be greater the sooner 

 the milk is treated after milking. The amount 

 of precipitant to be used, therefore, will largely 

 depend on the temperature. The action of heat 

 on j;he properties of milk is altogether of a most 

 interesting nature. When milk is heated to boiling 

 or to higher temperatures, it develops a peculiar 

 flavour a flavour especially unpleasant to many 

 people. Indeed, heating milk to even a considerably 

 lower temperature than boiling temperature imparts 

 this " cooked " flavour to milk. Thus if milk be 

 heated to 158 Fahr. for fifteen or twenty minutes it 

 acquires it. If, however, the milk be cooled again 

 it loses it. It is possible that both the smell and 

 flavour of milk which has been strongly heated is 



