220 UNSWEETENED CONDENSED MILK DEFECTS 



Effect of Degree of Concentration. Other conditions being 

 the same, the more concentrated the product the less the danger 

 of fat separation in the finished product. The reason for this 

 lies in the fact that with the concentration the viscosity and the 

 resistance force of the evaporated milk increase, hindering the 

 fat globules in their upward passage. This is partly offset by 

 the increase in the specific gravity of the product, but the in- 

 crease of the resistance force exerts a stronger influence against 

 separation of the fat, than the increase of the gravity force exerts 

 in favor of fat separation. 



However, as the concentration increases, the evaporated 

 milk becomes more sensitive to the sterilizing process and 

 beyond certain limits it would be necessary to reduce the tem- 

 perature or the length of exposure to heat, or both, in order to 

 prevent the more highly concentrated milk from becoming per- 

 manently curdy. If, in order to increase the viscosity, the degree 

 of concentration is carried so far that the sterilizing process has 

 to be shortened, nothing is gained but much may be lost. It 

 is obvious, therefore, that the degree of concentration does not 

 furnish a practical basis for controlling fat separation. 



Effect of the Sterilizing Process. Prolonged exposure of 

 the evaporated milk to the sterilizing heat tends to so change the 

 physical properties of the albuminoids, as to render the product 

 more viscous. Within the limits of the necessary sterilizing heat, 

 long exposure to moderate heat is more effective in this respect 

 than short exposure to a high degree of heat. Since the greater 

 viscosity tends to keep the fat globules from rising, the use of 

 a prolonged sterilizing process, in which the heat is applied 

 slowly, is more effective in preventing fat separation in the 

 evaporated milk than a rapid, short process, in which the tem- 

 perature used is very high. 



It should be understood from the discussion in previous 

 chapters that, in regulating the process of sterilization, the pro- 

 cessor should be governed by the condition and behavior of the 

 milk and that on the one hand the degree and duration of heat 

 should always be sufficient to insure absolute sterility of the 

 product, while on the other he must guard against the formation 

 of an unshakable curd. 1 



1 For detailed discussion see Chapter XI on "Sterilizing," page 120. 



