1. Introduction A challenge of single kernel testing using an instrument such as the Perten Single Kernel Characterisation System (SKCS) is to relate the results to actual breakage achieved during roller milling. As a step toward this, the resulting breakage materials from both SKCS and roller milling were studied. The particle size distribution (psd) produced on breakage of wheat by the SKCS itself was measured, and compared with the psd produced from First Break milling at different roll gaps and under different roll dispositions. Wheat varieties covering a wide hardness range were broken in the SKCS and in the Satake STR-100 test roller mill. Roll gaps of 0.3-0.8 mm were used under Sharp-to-Sharp (S-S) and Dull-to-Dull (D-D) roll dispositions. The size distributions of wheat particles milled using both systems were measured experimentally. Breakage of Wheat in the Single Kernel Characterisation System and during First Break Roller Milling I I Muhamad, C Fang and G M Campbell Satake Centre for Grain Process Engineering, Department of Chemical Engineering, UMIST, Manchester, M60 1QD, UK Conclusions Wheat was milled into a more uniform psd under a sharp-to-sharp roller disposition over the particle size range of 2122000 m than that were produced from milling under a dull-to- dull disposition. However, milling under dull-to-dull disposition gave a distribution with more larger and smaller particles and fewer in the middle size range. The particle size distribution from the SKCS was most similar to that produced from the roller mill at the largest roll gap of 0.8 mm under a dull-to-dull disposition. The effect of increasing kernel hardness in the roller milling, under disposition sharp-to-sharp was to increase the average size of the broken particles. The same effect was true for dull-to-dull milling. However, there is only a very slight effect of hardness on the resulting particle size, indicating that the actual breakage in the SKCS, or in dull-to-dull milling at a large roll gap, is relatively insensitive to wheat hardness. In the case of the SKCS, this indicates a design that gives a very positive and consistent crushing action to all wheat varieties. Acknowledgements – The authors gratefully acknowledge the EPSRC, the Universiti Teknologi Malaysia and the Satake Corporation of Japan for support for this project. Figure 4 shows the comparison of psds resulting from milling wheat samples of different hardness at different roll gaps under S-S and D-D dispositions and from SKCS. Under S-S disposition in the roller milling, the average size of the broken particles increased with the increase in kernel hardness. For D-D disposition, the same result was observed except at larger roll gaps, for which the average psd decreased slightly with increasing kernel hardness. From the SKCS, harder kernels resulted in smaller particles in the broken material. Objective: to investigate the breakage of wheat kernels in the SKCS and roller mill and to compare the resultant particle size distribution (psd) from both systems. Materials and Methods Nineteen samples of wheat of different hardnesses were conditioned to 16% moisture content, wb. All samples were milled in both the SKCS 4100 (Perten Instruments North America Inc., Springfield, IL) and the Satake STR-100 roller mill (Satake Corporation, Japan). Samples were milled on the roller mill under Sharp-to-Sharp (S-S) and Dull-to- Dull (D-D) dispositions and at six roll gaps (0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 mm), and the mass-based particle size distribution determined by sieve analysis. Wheat Kernel Breakage in the Single Kernel Characterisation System (SKCS 4100) Figure 1 shows the operating system of the SKCS that measures single kernel properties from crushing-profile. The force-deformation profile during the crushing of the kernel and the conductivity between the rotor and the electrically isolated crescent are measured against time. The information is algorithmically processed to provide the weight, size, moisture, and hardness of the kernel. Figure 1: The operation mechanism of the SKCS (Model 4100). The following also can be seen from Figure 2(b): The degree of breakage that occurred in the SKCS was much lower compared to the roller mill. Larger roll gaps produced less breakage of wheat kernels. The effect of roll gap was to change the balance between large and small particles The dull-to-dull disposition result was much closer to the line of equivalence than that from sharp-to-sharp. The closest agreement was obtained at the largest roll gap, 0.8 mm, under dull-to-dull milling. Wheat Kernel Breakage in the Roller Mill Roll disposition (Sharp-to-Sharp, S-S, or Dull-to-Dull, D-D) affects kernel breakage in the roller mill. D-D gives slippage between the flutes and the kernel, and thus imparts less shear strain than S-S. The planes with principal strain are shown in Figure 3. Results and Discussion Figure 2 (a) shows the cumulative psd of soft wheat, Consort from different milling operations; the SKCS, roller mill (S-S) and (D-D). Figure 3(b) shows the comparison of psd between roller milling with that from SKCS. Milling under a sharp-to-sharp disposition gave a relatively uniform size distribution over the particle size range of 2122000 m. By contrast, a dull-to-dull disposition gave a distribution with more larger and smaller particles and fewer in the middle size range. S-S D-D Figure 3: Forces experienced by kernels during sharp-to-sharp and dull-to-dull roller milling. (a) (b) Figure 2: (a) Cumulative Size Distributions of Consort wheat from different milling operations. (b) Comparison of psd from roller milling Consort at different roll gaps under a sharp-to-sharp and dull-to-dull dispositions with the psd obtained from the SKCS. (a) (b) (c) (d) (e) (f) Figure 4: Comparison of cumulative particle size distributions from SKCS and from roller mill at roll gaps: (a) 0.3, D-D; (b) 0.6, D-D; (c) 0.8, D-D; (d) 0.3, S-S; (e) 0.6, S-S; (f) 0.8, S-S at different wheat hardnesses. Figure 5 shows the values of x 50 and x 25 for the output from both the SKCS and the roller mill at 0.8 mm, D-D. Figure 5: Comparison of cumulative particle size distributions from SKCS and from roller mill at a roll gap of 0.8 mm under a dull-to-dull disposition. The values of x 50 and x 25 were very similar for both systems across a range of hardness values. Only a very slight effect of hardness on the resulting particle size is evident.