Effect of Brown Rice Temperature on the Rice Milling Quality During the Polishing Process

A cause for breakage of rice kernels during the whitening process could be assumed to be due to the produced heat. It is partly because of abrasion and friction of grains produced by contact against themselves and/or against cone and concave. In this study the effect of different temperatures of brown rice on rice kernels' breakage during the whitening process was investigated. Khazar cultivar was utilized throughout the experiment. Rough rice samples were dried up to 10-11 percent moisture content. Samples were hulled to the point of 90±2% through a rubber roll husker. The samples were packed in plastic bags and stored in –13, 5, 18, 25, 35, 45 and 55 ºC. Whitening was performed through a pilot friction type whitener lasting for three different time intervals of 30, 35, and 40 seconds. A factorial experiment consisting of two factors of brown rice temperatures and different whitening times as based on a completely randomized design of six replications was taken into account. The results revealed that rice temperatures up to 25 ºC did not significantly affect milled rice yield. However yeild decreased in temperatures exceeding 25 ºC. The reduction was 1.94% when temperature was raised to 55 ºC. Broken grain percentage increased for about 3.7% when temperature increased to the 55°C. The lowest brightness index was observed when temperature was set at 5-25 ºC. At – 13 ºC and at 35-55 ºC the brightness index was recorded higher than those at the other temperatures.