Influence of Kernel Shape and Size on the Packing Ratio and Compressibility of Hard Red Winter Wheat

Abstract

Grain compaction occurs during bin storage, and its determination is important for the grain mass estimation needed for inventory and auditing. The degree of compaction is dependent on grain type, bin type, moisture content, amount of grain, initial grain bulk density, coefficients of friction, lateral-to-vertical pressure coefficient, and variation in kernel size. Previous studies have correlated several of these parameters, such as bulk density and grain packing, with moisture content. This study investigated the influence of wheat kernel shape and size distribution on packing ratio and compressibility. Two dockage-free hard red winter (HRW) wheat samples, with no shrunken or broken kernels, were sieved using U.S. Tyler sieves #6, #7, #8, and #10, and the kernels retained on the sieves were used in the experiments. The kernel dimensional parameters and bulk sample parameters were measured, and additional derived parameters were calculated for each size fraction and variety. Packing ratio and compressibility of the size fractions and of binary and ternary mixtures of the size fractions were also determined for each variety. Packing ratio increased with larger kernel size, while compressibility decreased. Sphericity and flatness shape factor had strong positive linear relationships with packing ratio and strong negative relationships with compressibility, while elongation shape factor behaved the opposite way with packing ratio and compressibility. The higher the percentage mass of the larger kernel fraction in a mixture, the higher was its packing ratio and the lower its compressibility. The two tested varieties of wheat did not significantly differ in packing ratio and compressibility. These findings can be used in developing models for more accurate estimation of grain pack factor and to determine the mass of grain inside bins and other storage structures.