Effect of Moisture Content on Some Physical Properties of Grains

T important measurements used in determining the market grade of grain are moisture content and test weight per bushel (bulk density). Information on both test weight and moisture content is used in management decisions relative to conditioning, storing, and marketing of grain. The basic physical properties of the grain depend on the variety and type of grain, the location and soil fertility where the crop is grown, and the cultural and harvesting practices used. Kernel size and shape, bulk density, true density, and porosity are parameters used in studying hydrodynamic, aerodynamic, and heat and mass transfer problems in grain. Both physical and chemical changes in grains are related to environmental factors encountered in the field and in storage after the grain is harvested. Physical properties are affected by the treatment grain receives. For example, Bushuk and Hlynka (2)* found considerable hysteresis in weight and volume changes in wheat during adsorption and desorption of moisture. The flow of fluids through beds of grains, as well as the mechanical and bulk flow properties of grain itself, depend on the manner in which grains are packed and the amount of air void within the packed bed. Zink (8) and Lorenzen (3) evaluated the porosity of grains by the liquid displacement technique. Recently, Thompson and Isaacs (5) determined the porosity of grains with the air-comparison pycnometer. Particle shape influences void volume. Although many investigations have been aimed at quantitatively defining the shape of irregular particles, no universally accepted definition has yet been developed. Perhaps the term "sphericity" has been used most to describe particle shape. Seemingly the term was first used by Wadell (7), who