Reconstitution of dairy powders to high solids content in a stirred-tank: The effect of agitation

Experiments were carried out to investigate the effect of agitation on the reconstitution of a number of dairy powders in water to high solids content in a stirred tank. The results for whole-milk powder are only reported in this work, however the conclusions obtained were similar for all powders tested. The reconstitution quality, obtained immediately after mixing, was quantitatively assessed using tests for modified dispersibility and modified solubility index. The powder was fed onto the surface of the liquid, and as more powder was added, the sinkability of the powder decreased, limiting the solids content that could be attained. Powder sinkability was greatly improved by the formation and maintenance of a vortex at the liquid surface, and high shear action within the bulk of the liquid helped disperse and solubilise the powdered components. Vortex formation becomes more difficult at higher solids content due to the increase in viscosity, however careful design of the agitation system can enhance vortex formation at higher solids content.