216 UNSWEETENED CONDENSED MILK DEFECTS 



Lumps of Curd in Evaporated Milk. The danger of lump- 

 iness, or curdiness in evaporated milk is greatly augmented by 

 the fact that, in addition to the causes named under plain con- 

 densed bulk milk, the sterilizing process must be dealt with. 

 The high sterilizing temperature used, tends to precipitate the 

 proteids of milk, and the temperature cannot be reduced below 

 certain limits without impairing the keeping quality of the pro- 

 duct. Most of the evaporated milk, after sterilization, is sub- 

 jected to the shaking process in which the coagulum in the cans 

 is reduced to a homogeneous creamy fluid, provided that the curd 

 is not too hard. A curd will form in the sterilizer in the majority 

 of cases. If it is soft enough, so that it can be completely broken 

 up, no harm is done. If it is so firm that mechanical shaking 

 fails to cause it to disappear, then the evaporated milk will reach 

 the market in lumpy condition and is difficult to sell. 



Effect of Quality of Fresh Milk. The quality of fresh milk 

 is all important in preventing lumpy evaporated milk. The milk 

 must come from healthy cows in good, normal physical condition. 

 It must not contain colostrum milk nor be stripper milk and it 

 must receive the best of care on the farm and reach the factory 

 perfectly sweet. Milk that is not of high quality in every respect 

 should not be received at the factory. 1 



Effect of Concentration. The more concentrated the evap- 

 orated milk, the greater the danger of lumpiness. All the con- 

 ditions causing lumpiness are intensified by the degree of con- 

 centration. The manufacturer must, therefore, study the be- 

 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 



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 



i For detailed discussion of relation of quality of fresh milk to curdiness of 

 evaporated milk see Chapter VIII on "Manufacture of Evaporated Milk," "Quality 

 of Fresh Milk," p. 104. 



