Practical considerations for reconstituting dairy powders to high solids content in a stirred-tank

This work considers the following practical aspects of reconstituting dairy powders to high solids content in a stirred-tank: solubility constraints, powder properties vs agitation, viscosity and age-thickening constraints. The powders investigated were skim-milk, whole-milk, agglomerated whole-milk and whey. At a given temperature, component solubilities, in particular lactose, place an upper limit on how high a solids content can be obtained. The powders tested displayed differences in measured values of wettability, sinkability and dispersibility, however their reconstitution ability to high solids content was similar. The limiting factors, on how high a solids content that could be attained, were either solubility limit or loss of vortex. For reconstituted skim-milk, the viscosity increases exponentially with solids contents and will limit vortex formation and powder sinkability. In addition, at higher solids content, significant age-thickening of reconstituted skim-milk occurred, whereby the viscosity of a 50% solids solution increased 3.5 times in 1 h, thus making the solution more difficult to handle.