A study of the cohesion of dairy powders

Milk powder deposition is an area of importance to the dairy industry as it affects the efficiency of the spray drying process. An unconfined yield te st was used to measure the cohesion of dairy powders to determine the influ ence of powder composition, temperature, moisture content and particle size . As an index of cohesion, values of unconfined yield stress were obtained for whole milk powder (WMP) and skim milk powder (SMP). Dry WMP was found t o be more cohesive than dry SMP with increasing temperature, which indicate s the influence of fat in the cohesive mechanism in WMP. Particle size also affected the cohesion of dairy powders, cohesion being reduced as the part icle size increased. The glass transition effect was isolated when testing for the effect of moisture by using a vibrated fluidised bed technique. Thi s was highlighted by the change in the cohesion transition temperature betw een two WMPs with different moisture contents. An increase in moisture cont ent, particularly above 6 wt% increased the cohesion of WMP, possibly as a result of the formation of liquid bridges; these results confirm the only o ther previous work reported in the literature. (C) 1999 Elsevier Science Lt d. All rights reserved.