CoMPOSITION AND PROPERTIES OF MiLK POWDERS 325 
unpossible to reduce the dried milk to a homogeneous fluid, similar 
to normal fresh milk. ‘The fat in such milk will rise to the surface 
quickly, similar to the fat in a mixture of oil and water. 
Keeping Quality of Milk Powders. 
Moisture Content——(ne of the fundamental reasons for 
which milk is reduced to a dry powder lies in the efforts of the 
manufacturer to preserve it. 
Bacteria and other micro-organisms require moisture to grow, 
thrive and accomplish their work of decomposing the substances in 
which and on which they live. In the absence of moisture bacterial 
action ceases. 
In properly desiccated milk powders, such as are now manu- 
factured and placed upon the market, the percentage of moisture 
has been reduced to a point that precludes the possibility of bac- 
terial decomposition. If these desiccated milk powders are packed 
and stored in such a manner as to protect them against dampness, 
they may reasonably be expected to keep indefinitely insofar as 
their keeping quality depends on freedom from bacterial action. 
Milk powders with excessive moisture content and milk powders 
that are exposed to dampness, on the other hand, are prone to be- 
come lumpy, moldy and to develop diverse undesirable flavors. 
Air, Light and Heat; Relation to Stale Flavor, Tallowy and 
Rancid Flaveor.—In spite of the fact that the low moisture con- 
tent renders milk powders practically immune to bacterial action, 
they are subject to deterioration with age when certain other con- 
ditions, such as air, hght and heat are favorable, or when metals and 
metallic salts are’ present, or both, and experience has amply dem- 
onstrated that practically all milk powders made from the usual 
quality of milk under the present methods of manufacture and 
packing, and usual conditions incident to storage, develop a dis- 
agreeable stale flavor, which often degenerates into a tallowy or so- 
called rancid flavor with age. 
Exact data showing the fundamental changes which these pow- 
ders undergo are not available, but the findings of Rogers, Hunziker 
and others,’ as the result of extensive experimental studies of the 
keeping quality of butter strongly suggest, that these changes are 
of chemical rather than of biological nature and that oxidation of 
1Hunziker. The Butter Industry, 1920. 
