86 SWEETENED CONDENSED MILK CONDENSING 



Rapid evaporation cannot take place until the milk is brought 

 to the boiling point and is kept there until evaporation is Com- 

 pleted. Under atmospheric pressure and at the sea level, the 

 boiling point of water is 212 degrees F., the boiling point of milk 

 is very slightly higher, about 214 degrees F. Evaporation of milk 

 under atmospheric pressure in an open kettle, however, is a 

 relatively slow process, requiring a long time and large appara- 

 tus. Furthermore, exposure of the milk to 212 to 214 degrees 

 F. long enough to complete evaporation would render the prod- 

 uct unsuitable for market. The properties of some of its ingre- 

 dients are altered, the product would assume a dark color and 

 a marked cooked flavor as the result of the effect of heat. All 

 of these objections are minimized and partly avoided by lower- 

 ing the boiling point of milk. These objections, howtver, do 

 not apply to evaporation under atmospheric pressure by film 

 treatment, as is the case with the Continuous Concentrator de- 

 scribed in Chapter XIV. 



Relation of Pressure to Boiling Point. The temperature at 

 which milk boils depends on the pressure to which it is exposed. 



