EVAPORATED MILK CONDENSING 119 



pan must be relatively small. This milk foams more in the pan 

 than the heavier sweetened condensed milk. This factor reduces 

 therefore, the capacity of the pan. If the milk is not cooled upon 

 arrival, but is transferred immediately to the hot wells, it is 

 advisable to use numerous small wells, rather than but one or 

 a few large ones. These small wells fill rapidly and the milk 

 can be heated without delay. This system makes it possible to 

 render the bacteria inactive and harmless practically as soon 

 as the milk arrives, minimizing the danger of acid formation. 1 

 Steam may be saved if the milk is forewarmed by running 

 it through coils inclosed in a chamber of exhaust steam, but the 

 coils increase the labor and difficulty of cleaning. It is best to 

 heat the milk to as near the boiling point as possible and hold 

 it there for five to ten minutes, provided that the capacity of the 

 factory warrants this delay. In this heating the casein ot the 

 milk is somewhat changed. There occurs partial, though invis- 

 ible, precipitation, and the higher the temperature to which the 

 milk is heated, the more pronounced is this change. This change 

 is desirable, because the casein thereby surrenders, to a limited 

 extent, its power and tendency to form a firm curd in the ster- 

 ilizer. See also Chapter XI on " Sterilizing." 



CONDENSING. 



The same apparatus, the vacuum pan and pump, is used 

 for condensing the milk, and the process of condensing is prin- 

 cipally the same, as in the case of sweetened condensed milk. 

 The fresh milk is condensed at the ratio of two to two and one- 

 half parts of fresh milk to one part of condensed milk. In some 

 factories it is customary to superheat the milk in the pan before 

 it is drawn off, i. e., the steam to the jacket and coils is shut off, 

 the water valve is closed, the vacuum pump is stopped and 

 "live" steam is passed into the condensed milk. When the 

 vacuum has dropped to about six to eight inches, and the tem- 

 perature has risen to 180 to 200 degrees F. the superheating is 

 stopped, the steam is turned off, the vacuum pump is started 

 again, and the condensing is completed. The superheating is fre- 

 quently also done after the evaporated milk has been drawn 



1 See also Cooling Milk and Standardization. 



