1. Abstract The particle size distribution (psd) produced by breakage of wheat in the Perten Single Kernel Characterisation System (SKCS) was measured using sonic sifting, for a range of wheat varieties, kernel sizes and moisture contents. At moisture contents of 16% wb, the psd produced by the SKCS was very evenly spread over the range 106-3350 m. Hard wheats gave slightly smaller average particle sizes in the broken material (this was unexpected and contrasts with First Break roller milling, for which hard wheats give larger output particles than soft wheats), but the variation in psd among different wheat varieties was surprisingly small.. Kernel size similarly gave little difference in the output psd. The effect of increasing the moisture content from 9 to 17% wb was to increase the average output particle size greatly; moist kernels do not break so readily in the SKCS. Wheat Breakage in the Single Kernel Characterisation System Ida I Muhamad and G M Campbell Satake Centre for Grain Process Engineering, Department of Chemical Engineering, UMIST, Manchester, M60 1QD, UK Effect of Kernel Size on Particle Size Distribution Figure 3 shows the particle size distributions resulting from milling wheat samples of Hereward (hard) and Consort (soft) in the SKCS. It was observed that Large kernels went through slightly more breakage and produced smaller particles than small kernels. The resultant size distribution shows a very close linear pattern over the whole size range. The difference in particle size as an effect of kernel size was small for about only 100 microns of the overall breakage. Materials and Method Wheat samples used in this study were winter wheat cultivars obtained from ADAS. Samples were divided into three sets. Set 1 consists of 17 varieties of wheat within a range of hardness from soft to hard conditioned at 16% moisture. Set 2 was samples of Hereward and Consort wheat separated into three different kernel sizes: 2.25-2.50 mm; 2.50-2.75 mm and 2.75-3.00 mm. Set 3 consists of Soissons wheat samples conditioned into nine different tempering moistures: 9, 10, 11, 12, 13, 14, 15, 16 and 17% (wet basis). Samples were milled the SKCS 4100, and the mass-based particle size distribution determined by sonic sifting analysis (GilSonic Autosiever). 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). Effect of Moisture on Particle Breakage Figure 4 shows the effect of moisture content on the breakage in the SKCS. The following can be seen from Figure 4: It is clear that for each distinguishable line, the size distribution increased with the increase in moisture content in Figure 4a. By comparing Figure 4a with Figure 4b, it is clear that the magnitude of change in size distribution with breakage is greater in highly moisturised samples compared to that of lower moisture content. This implies that the extent of endosperm softening increases with more incorporation of water into kernels during tempering process prior to breakage. Thus, the increase in moisture content caused the increase in breakage that showed in the increase of psd. Figure 2: (a) Cumulative size distribution of wheat varieties of different hardness conditioned at 16% moisture. (b) x 25, x 50 and x 75 versus SKCS hardness of 17 wheat varieties conditioned at 16% moisture Conclusions The SKCS breaks samples consistently, resulting in similar size distributions among all varieties within a range of hardness. The mode of breakage in the SKCS is very consistent regardless of the hardness of wheat used. The effect of hardness and kernel size on particle size distribution were small but moisture content did affect the breakage in the SKCS 4100 significantly. Acknowledgements - The authors gratefully acknowledge the EPSRC, the Universiti Teknologi Malaysia and the Satake Corporation of Japan for support for this research project. Results and Discussion (a) (b) Consort Hereward (a) (b) Figure 3: (a) Cumulative size distribution of Hereward and Consort wheat of different kernel sizes at tempering moisture 16% (b) x 50 versus kernel sizes of Consort and Hereward wheat at different moistures Figure 4: (a) Cumulative size distribution of Soissons wheat at different tempering moistures (b) x 25, x 50 and x 75 versus versus different tempering moistures of Soissons wheat Effect of Hardness on Wheat Kernel Breakage in the SKCS Figure 2 shows the size distribution obtained from different wheat varieties milled in the SKCS. It shows that: Hard wheats gave slightly smaller average particle sizes in the broken material. This was contrasts with First Break roller milling, for which hard wheats give larger output particles than soft wheats. However the variation in psd among different wheat varieties was surprisingly small. At moisture contents of 16% wb, the psd produced by the SKCS was very evenly spread over the range 106-3350 m. The difference in x 50 increased by the increase in moisture. However, the overall difference in psd was very small.