UNSWEETENED CONDENSED MILK DEFECTS 255 



known fact, established by practical experience in processing, 

 and by analyses of different brands of evaporated milk, that in 

 some European countries, milk can be condensed to a much 

 higher degree of concentration than in most sections of this 

 country, without becoming permanently curdy. 



Effect of Forewarming or Preheating on Curdling. As ex- 

 plained in Chapter XI on "Sterilizing/* under "Factors that 

 Decrease Viscosity of Evaporated Milk," the readiness with 

 which milk coagulates in the sterilizer is diminished by lengthen- 

 ing the period of preheating in the forewarmer, or by raising the 

 temperature of preheating, or both. And vice versa, the shorter 

 the period of preheating and the lower the temperature (below 

 210 degrees F.) to which the milk is foreWarmed, other conditions 

 being the same, the greater the danger of curdling in the steril- 

 izer. 



It is not improbable that here again the modification of the 

 balance of the calcium and magnesium with the phosphates and 

 citrates, may be the fundamental cause of these phenomena. 

 In this case the longer exposure to the forewarming heat, or the 

 higher temperature of forewarming, or both, may have the effect 

 of lowering the soluble calcium content by precipitating part of 

 it as insoluble calcium phosphate. If coagulation is due to an 

 excess of calcium or magnesium, as it usually is, then this lower- 

 ing of the calcium content, as the result of preheating, will mini* 

 mize the danger of coagulation in the sterilizer. 



Effect of Addition of Water on Curdling. Addition of ex- 

 traneous water to the evaporated milk lessens the intensity of 

 coagulation in the sterilizer. This is a matter pretty generally 

 understood by the experienced operator, as pointed out in Chapter 

 XI on "Sterilizing" under "Factors which- Decrease Viscosity 

 and Tendency to Curdle." It is due to the dilution of both the 

 casein and the serum in milk. 



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



1 For detailed discussion of relation of quality of fresh milk to curdinese 

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

 "Quality of Fresh Milk." 



