Effects of Viscosity and Temperature on the Foaming Characteristics of Concentrated Whole Milk

Summary To better understand continuous vacuum foam-drying of whole milk, a study of milk concentrate foams was undertaken. An apparatus was developed for measuring two independent parameters, foaming ability and stability. Foaming ability was defined as the initial height of foams immediately after formation in a column and stability was defined as the rate of subsidence of these foams. Foam determinations were made on several concentrate batches of 44 ± 1.5% solids between 50 and 95 F. Variations in concentrate viscosity were caused by temperature changes and intrinsic batch differences and ranged from 70 to 800 centipoises. Foam stability was well correlated with concentrate viscosity. Foaming ability of each batch was correlated with temperature and minima were 70 F. A complex correlation of viscosity and temperature described foaming ability for all batches. These experiments confirmed the importance of viscosity and temperature as control parameters in the vacuum foam-drying process and also showed that final foam structure is established early in the drying operation.