Effect of temperature on the reconstitution of milk powder to high solids content in a stirred-tank

When reconstituting milk powders in stirred-tanks to form high solids content solutions, the sinking of powder into the water surface becomes more difficult due to the increase in solids content and the corresponding increase in solution viscosity. Creation and maintenance of a vortex will greatly improve the sinkability of the powder. This work investigates how solution temperature, in the range of 20 to 70°C, influences reconstitution to high solids content, in particular, powder sinkability and impeller power requirement. Higher temperatures have a pronounced affect at higher solids content, by allowing for increased solids content to be attained before the occurrence of exponential increase in viscosity and impeller power requirement. At 20°C, a sharp increase in impeller power requirement occurred at about 42% solids content, while at 70°C, this occurred at around 55% solid content. Higher temperatures will also allow higher solids content solutions to be attained before the solution gels and behaves more like a solid. At 20°C, this was at about 53.5% solids content, while 61.5% solids content was obtained at 70°C before prevention of vortex formation occurred. Higher temperatures also reduce the age-thickening effect during reconstitution and subsequent processing.