Separation of Empty Kernels Using the Physical Properties of Short-Grain Rough Rice

Highlights Physical properties of whole rough rice and empty kernels of five short-grain rice varieties were measured. Geometric traits of kernels could not be used for the separation of empty kernels from whole kernels. Separation of kernels can be achieved based on weight difference between whole and empty kernels. Air velocity in pre-cleaners should be set between the terminal velocities of whole and empty kernels. Abstract . The key factors required to separate empty kernels (EKs) from whole kernels (WKs) were investigated in rough rice varieties. The geometric properties and 1000-grain weight of rough rice WKs and EKs of five varieties of short-grain rice with varying moisture content were measured. The terminal velocities for floating and dropping of WKs and EKs were tested in a vertical air column to identify the aerodynamic separation characteristics. The separation of EKs from WKs based on kernel geometric characteristics was not possible because of insignificant differences between WKs and EKs in terms of length, width, roundness, and other geometric characteristics. The 1000-grain weight of WKs and EKs ranged from 23.7 to 29.2 g and from 3.9 to 8.5 g, respectively. Linear regression equations were used to determine the relationship between terminal velocity and moisture content in both floating and dropping phase. The allowable floating and dropping terminal velocity range for separating WKs and EKs ranged from 5.0 to 7.6 m s-1 and from 2.1 to 4.1 m s-1, respectively. Moisture content, and especially, kernel type and terminal velocity type had significant effects on the terminal velocity. Keywords: Empty kernel, Physical property, Rough rice, Separating, Terminal velocity.