256 UNSWEETENED CONDENSED MILK DEFECTS 



havior of his product at different degrees of concentration, and 

 then decide how much evaporation it will stand without develop- 

 ing subsequently a permanent curd in the sterilizer. 1 



It is obvious that any excess or deficiency of calcium, or 

 any excess of acid present in the original milk, is magnified in 

 direct proportion as the concentration increases. Therefore, the 

 higher the concentration, the more difficult it is to put the evap- 

 orated milk through the sterilizing process without the formation 

 of a permanent curd. 



Effect of Sterilization. The coagulum is formed in the 

 sterilizer. The higher the temperature, other conditions being 

 the same, the firmer the curd. The lowest temperature that will 

 efficiently sterilize the evaporated milk should, therefore, be 

 used. Since the sterilizing temperature to be maintained cannot 

 be modified below certain limits, it is necessary, when the milk 

 is very sensitive to the heat, to lower the degree of concentration. 

 In some factories fractional sterilization is resorted to with 

 batches of milk that are suspicious. By so doing, lower tem- 

 peratures can be used effectively, but this process calls for much 

 more labor, increases the cost of manufacture and decreases the 

 capacity of the factory. 



Effect of Fractional Curdling. Experience has shown that, 

 if the proteids in evaporated milk are partly precipitated by heat 

 before the milk reaches the sterilizer, the curd or lumps formed 

 in the sterilizer are less firm and can be shaken out more readily. 

 It is, therefore, advisable to heat the milk in the forewarmers to 

 as near the boiling point as possible and to hold it at that tem- 

 perature for at least five minutes before it is drawn into the pan. 

 The superheating of the evaporated milk before it leaves the pan 

 is an additional safeguard against the formation of excessive curd 

 in the sterilizer. 



Effect of Homogenizing Evaporated Milk. Excessive pres- 

 sure in the homogenizer tends to so change the physical prop- 

 erties of the casein as to render it more sensitive to the steriliz- 

 ing process. Evaporated milk, homogenized under excessive 

 pressure almost invariably forms a firm, unshakable curd in the 



1 For detailed discussion see Chapter VIII, on "Striking," and Chapter XI, 

 on "Sterilizing." 



