On Predicting Roller Milling Performance V: Effect of Moisture Content on the Particle Size Distribution from First Break Milling of Wheat

Extended breakage functions incorporating both single kernel size and moisture content were determined for First Break milling of hard and soft wheats under a sharp-to-sharp disposition. A moisture correction function was constructed by milling narrow size fractions of wheat tempered to different moisture contents, and subtracting the breakage function at a base moisture content of 16% from that at other moisture contents. The effect of adding moisture was to change an initially inverted U-shaped distribution at low moisture contents to a linear distribution at 16% moisture, then to a U-shaped distribution at higher moisture contents, reminiscent of the particle size distributions produced by dull-to-dull milling. The extended breakage functions were used to predict milling of unseparated feed samples at different roll gaps and moisture contents. In addition, mixtures of hard wheat at 14% moisture and soft wheat at 20% moisture, mixed in different proportions, were milled and the resulting particle size distributions compared with predictions. Excellent predictions were obtained in all cases. This confirms the independent breakage of kernels during First Break milling, and demonstrates the potential of the breakage function approach for interpreting single kernel data in terms of predictions of milling performance.