Wet grinding characteristics of soybean for soymilk extraction

Wet grinding of hydrated soybean was carried out with mixer grinder, stone grinder and colloid mill which revealed that particle size had a profound effect on the protein recovery in the extracted milk with a maximum recovery of 89.3%. Greater reduction in particle size was achieved with mixer grinder (180 μm) with 5 min of grinding while reduction was not significant beyond 18 min (233 μm) in stone grinder. Specific energy consumption in colloid mill was only one-fourth of the mixer grinder while stone grinder required twice the energy. Although Kick's, Rittinger's and Bond's laws could not be applied for total grinding duration, all the three classical laws were found suitable after the initial grain break-up period (2 min). Temperature and duration of thermal treatment given during hot extraction influenced protein recovery and viscosity of soymilk. The results suggest that colloid mill is a potential device for industrial scale operation.