326 COMPOSITION AND PROPERTIES OF MII^K 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. 1 



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 lig'ht, 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 



1 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. 



