Studies on physical and engineering properties of minor millets for processing equipment design

Abstract:

Processing equipment for minor millets has traditionally been derived from rice and wheat hardware, and the mismatch in grain geometry has limited throughput and product quality. This research measured the key physical and engineering properties of seven minor millets - finger, foxtail, kodo, little, barnyard, proso and brown top - and used the values to propose equipment design parameters suited to small-scale processors in the East African highlands. Moisture content, 1000-kernel weight, grain dimensions, sphericity, bulk and true density, angle of repose, coefficient of static friction on four surfaces, porosity and terminal velocity were measured on three replicates per sample. Mean 1000-kernel weight ranged from 2.84 g in finger millet to 5.74 g in proso millet. Sphericity varied from 0.71 to 0.93, bulk density from 712 to 798 kg m⁻³, and angle of repose from 22.4° to 31.6°. Friction coefficient was highest on rubber and lowest on stainless steel across all seven species. Terminal velocity ranged between 5.2 and 8.4 m s⁻¹. The data enabled a design decision table for sieve aperture, hopper angle and conveyor speed for each millet. The findings support the development of dedicated minor-millet processing lines at micro and small scale.