The Keeping Quality, Solubility, and Density of Powdered Whole Milk in Relation to Some Variations in the Manufacturing Process. II. Solubility and Density

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Abstract
Powdered milk was made by use of an exptl. spray dryer from milk preheated at 160 and 170[degree]F for 30 min. and 170 and 180[degree]F for 10 min. For each temp. 4-6 lots were split into 2 batches, one batch being concd. to approx. 20% total solids and the 2d batch to approx. 40% total solids. Solubility indices were detd. on the fresh powder and at intervals of 1, 2 and 6 mos. storage at 45 and 100[degree]F. The powder made from the 40% concn. was slightly more soluble than the powder made from the 20% concn. The powder made from the 40% concn. was 100% soluble at the end of 6 mos. storage at 45[degree]F. Storage at 100[degree]F resulted in rapid loss of solubility for the powder made from milk preheated at 180[degree]F for 10 min. The powder made from milk preheated at the other temps. and concns. to 40% did not decrease in solubility to any appreciable degree when stored at 100[degree]F for 6 mos. The densities of the powders were detd. by calibrating 8% Babcock milk test bottles at 25[degree]C. 7-11 g. of powder were placed into the test bottles and the wt. of powder detd. Light mineral oil (No. 1) was used as the displacing medium. Interstitial and adsorbed air was removed by 20 in. vacuum for 20 min. The milk powders increased in density with increasing preconcn. of the milk. The powders made from milk concd. to 40% total solids were easier to reconstitute, did not take up as much space and did not as readily develop a high electrostatic charge as did powders made from the 20% total solids concn. Under conditions of the expt., 95% of the powder particles made from the 40% total solids concentrate were under 10 u. in diameter.