Humidity Equilibria of Milk Powders

Summary 1.Data are given showing the moisture content of various milk powders at equilibrium in vapor pressures corresponding to humidities from 10 to 80 per cent at 25°C. 2.It is shown that the absorption of moisture by milk powder irrespective of the method of manufacture, apparently proceeds according to certain fundamental laws governing absorption by collodial matter. 3.The data show that at humidities above 50 per cent the initial moisture absorption is very rapid, and at humidities between 50 and 70 per cent this initial absorption is not retained by the powder. When the maximum is reached a dehydration process begins and extends over a period of months before equilibrium is established at a lower level. 4.The dehydration results obtained after milk powder had been subjected to a relatively high moisture content for a period of three weeks, show a different moisture retention at the various humidities than was shown during hydration. 5.The absorptive properties of milk powder were found to be altered by excessive heating and previous saturation. 6.Milk powders with variable fat content are shown to possess different capacities for moisture absorption and retention. The absorptive ability decreases with increased fat content and correspondingly lower protein content.