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The Removal of the Sorbed Gases in Dried Milks¹

Division of Dairy Research Laboratories, Bureau of Dairy Industry; Agricultural Research Administration, U. S. Department of Agriculture

ABSTRACT

The amount of sorbed (occluded, adsorbed, and dissolved) gases in dried milks varies greatly with the fineness of the product. Dried milks made from milks of normal concentration contain a relatively large amount of sorbed gas, which decreases greatly as the concentration of the milk used is increased from 9 to 38 per cent solids.

A large percentage of the sorbed gases can be removed by evacuation for relatively short periods of time within the practical range of temperatures of 20° to 40° C. The remainder only can be desorbed very slowly as the time of evacuation is extended.

The composition of the sorbed gas varies with the storage time of the dried milk in an atmosphere of air. Freshly made products seem to have percentage concentrations of oxygen greater than air and very low percentage concentrations of carbon dioxide. In older products, the proportion of oxygen in the sorbed gases is but slightly greater than that in air and the proportion of carbon dioxide is greater than can be accounted for if the gases are occluded air.

The results indicate that most of the residual gases are held by adsorption forces.

A large proportion of the oxygen of the sorbed gas may be removed by successive evacuations, with periods of several days between to allow for diffusion of the oxygen into a nitrogen atmosphere. The results indicate that two cycles of evacuation—filling with nitrogen, and holding for 3 to 4 days—remove a high percentage of the oxygen of the sorbed gases.

¹ Data presented at the Technical Conference of the Dry Whole Milk and Ice Cream Mix Industry under the auspices of the QMC Subsistence Research and Development Laboratory, January 23–25, 1945, Chicago, Illinois.