Effect of roll fluting disposition and roll gap on breakage of wheat kernels during first-break roller milling

Breakage of wheat kernels during first-break roller milling depends on many factors, including the disposition of the fluted rolls: sharp-to-sharp, sharp-to-dull, dull-to-sharp, or dull-to-dull. Wheat kernel breakage under different dispositions during milling was studied using high-speed video imaging. The results show significant slippage between kernels and the flutes when a dull working angle is used, especially when the dull angle is on the fast roll. Experiments were conducted to compare the size distributions resulting from the four dispositions. Representative hard and soft wheat cultivars were milled using fluted rolls at five different roll gaps, and the resulting size distribution of the milled stocks was measured by sieve analysis. A sharp-to-sharp disposition gave a relatively uniform or straight line size distribution over the particle size range of 212-2,000 μm. By contrast, a dull-to-dull disposition gave a U-shaped distribution with more larger and smaller particles and fewer in the middle size range. The size distributions from the other two dispositions lay between these, giving a transition from a straight-line distribution for sharp-to-sharp disposition, slightly U-shaped for sharp-to-dull, more curved for dull-to-sharp, and highly U-shaped for dull-to-dull. The effect of roll gap was to change the balance between large and small particles.