Quality Characteristics of Medium‐Grain Rice Milled in a Three‐Break Commercial Milling System

Abstract

Within rice varieties, individual kernels vary in size. The effect of kernel size on milling performance and quality has been studied (Matthews and Spadaro 1976, Wadsworth et al 1982, Sun and Siebenmorgen 1993, Chen and Siebenmorgen 1997). These studies focused on long-grain rice milled in single-break, laboratory or commercial-scale friction mills. As rice was milled from a low to high degree of milling (DOM) level, more surface bran was removed from thin kernels than from thick kernels, and thin kernels were broken at a greater rate than thick kernels. There is an increasing trend in use of multibreak milling systems by the rice industry. Chen et al (1998) conducted research on the milling performance of long-grain rice in both singleand triplebreak commercial milling systems. For both milling systems, the surface lipids content (SLC) and protein content of milled rice varied significantly across kernel thickness fractions. SLC was influenced by DOM level more than by kernel thickness, whereas protein content was influenced by thickness more than by DOM level. As milling progressed from a low to high DOM level, thin kernels were milled at a greater bran removal rate than thick kernels, as indicated by SLC. However, protein content decreased much more uniformly across thickness fractions than did SLC during milling. The studies mentioned above were limited to long-grain rice. The objective of the current work was to investigate the bran removal characteristics of medium-grain rice milled in a multibreak commercial milling system.