COMPOSITION AND PROPERTIES OF* MILK POWDERS 325 



impossible 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 fa$ in a mixture of oil and water. 



Keeping Quality of Milk Powders. 



^ Moisture Content. One 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 Flavor. 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, light 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, 1 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 



1 Hunziker. The Butter Industry, 1920. 



