Condensed Mii,k and Mii,k Powder 169 



tories, newly established, summer milk is largely produced and the 

 majority of cows freshen in the spring. This causes a marked 

 increase of the size of the average fat globules in early summer, 

 rendering the manufacture of evaporated milk, that does not sepa- 

 rate its fat, more difficult. 



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 increase 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 temperature or the length 

 of exposure to heat, or both, in order to prevent the more highly 

 concentrated milk from becoming permanently 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 temperature used is very high. 



It should be understood from the discussion in previous chapters 

 that, in regulating the process of sterilization, the processor 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 suf- 



