170 Chemical Composition 



shaking. The casein in evaporated milk does not respond to the 

 action of rennet as does the casein in fresh milk. 



Milk Sugar. — The milk sugar is present in per cent corre- 

 sponding with that of the original milk, times the degree of con- 

 centration. A portion of it has undergone oxidation (carameliza- 

 tion) due to the high sterilizing temperatures. It gives to the 

 evaporated milk a yellow^ to light brown color. The higher the 

 sterilizing temperature and the longer the exposure of the evapo- 

 rated milk to this heat, the darker is its color. 



Ash. — The mineral constituents also are present in nearly 

 the same proportion to the other solids, as in fresh milk. They 

 are largely rendered insoluble by the sterilizing process. The 

 lime constituents frequently are found in the bottom of the cans 

 in the form of hard, whitish, insoluble granules. 



Since the ash in normal fresh milk is practically constant, 

 averaging about .70 per cent, the per cent of ash in the evapo- 

 rated milk is frequently used as a factor in determining the 

 degree of concentration. The results may, however, be very 

 misleading, since, when the ash is precipitated in the form of 

 granules, it is practically impossible to mix it back into the milk 

 in order to obtain a representative sample for analysis. 



The Specific Gravity ranges from 1.05 to 1.08, according to 

 the degree of concentration and the specific gravity of the original 

 milk. It averages about 1.065. 



Plain condensed bulk milk is of very varying composition, 

 depending largely on the degree of concentration and the per 

 cent of fat present. It is usually made from partly or wholly 

 skimmed milk and is condensed at the ratio of 3 to 4 parts of 

 fresh milk to 1 part of condensed milk. The same fact applies 

 to the composition of concentrated milk. 



