326 COMPOSITION AND PROPERTIES OF MinK POWDERS 
one or more of the constituents of these products plays an important 
role. Success in the manufacture of milk powders of superior 
keeping quality, therefore, demands also the protection of the prod- 
uct against agencies that invite oxidation. ' 
Exclusion of Air.—The oxidizing power of air is well known. 
Milk powder exposed to atmospheric air will not keep. It soon de- 
velops a stale flavor, and if it contains a considerable percentage of 
butterfat it becomes tallowy. 
For this reason milk powder should be, and usually is, packed 
in such a manner as to exclude the outside air as much as possible. 
The powder packed in bulk is sealed in barrels lined with heavy 
paper. Smaller packages consist of tin cans, or fibre cans with tin 
ends and friction caps. 
Unfortunately the body of the milk powder itself is not en- 
tirely free from air, so that unless packed under vacuum there al- 
ways is some air in the package. While protection against free ex- 
posure to outside air, by proper packing, greatly minimizes the de- 
teriorating action, and does distinctly enhance the keeping quality 
of the powder, the air present in the sealed package is sufficient to 
cause slow deterioration when other conditions, such as heat or 
metallic salts, or both, are present. The packing of milk powder in 
vacuo would undoubtedly assist in preserving the milk powder. 
Exclusion of Light.—The rays of light intensify the oxidiz- 
ing action of the air. It is, therefore, important that milk powder 
be kept in the dark. This is automatically accomplished by sealing 
it in the usual commercial packages. If the powder must be held 
in the factory for a considerable number of hours before packing, 
it should be kept in covered containers. Remnant barrels, or other 
broken packages in the home or in industrial establishments using 
milk powder should be kept tightly covered. 
Effect of Heat.—Heat, similar as light, intensifies the 
oxidizing action of air and of other oxidizers and catalizers. Milk 
powder kept at relatively high temperatures becomes stale and de- 
velops other defects quicker than milk powder kept in the cold. 
Metals and Metallic Salts.—Certain metals and their alloys 
a \The sensitiveness of most of the spray process milk powders toward 
oxidizing agents is augmented by the fact the atomizing process under high 
pressure causes a subdivision of .the fat globules, depriving the fat of at 
least a portion of the protective gelatinous layer which surrounds each orig- 
inal fat globule, thereby exposing the fat more directly to the destructive 
oxidizing agents. 
