Effect of Free and Bound Water and Consolidation Process Time on the Strength of Food Powders

Abstract

This study examined the effect of particle size, moisture content, mixing, and consolidation time on the flow and mechanical behaviour of bulk rice assessed using a Schulze Ring Shear Tester RST-01. Three rice fractions: 0.5–1.0 mm, >1.0 mm, and whole grains were tested at 8% and 20% moisture. Fine particles showed high flowability in dry conditions but exhibited a strong increase in cohesion and a significant drop in the flow function coefficient at the higher moisture content. Unexpectedly, whole grains showed the highest shear resistance after moistening and consolidation, which can be attributed to force chain formation and localized capillary bonding. Extended mixing and consolidation further stabilized the structure and reduced flowability. These findings indicate that larger particles can exhibit greater mechanical stability in moist conditions. The results emphasize the need to consider particle size and preparation history in the handling and storage of bulk materials.