106 EVAPORATED MILK CONDENSING 



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 of 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 steril- 

 izer. 



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, 

 trte 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 F. the superheating is stopped, 

 the steam is turned off, the vacuum pump is started again, and 

 the condensing is completed. The superheating is frequently 

 also done after the evaporated milk has been drawn from the 

 pan. In this case, the process of evaporation is usually carried 

 slightly beyond the desired density of the finished product, the 

 evaporated milk is drawn from the pan into an open vat or 

 kettle where steam is turned direct into the milk until the super- 

 heating is completed, which is indicated by its greater consist- 

 ency and the slightly flaky condition of the curd. Then water is 

 added to the superheated evaporated milk to bring the product 

 back to the desired density. 



The chief purpose of superheating is to partly precipitate 



1 See also Cooling Milk, p. 52, and Standardization, p. 253. 



