Two-Year Analysis of the Effects of Hot-Air Drying Temperature and Initial Grain Moisture Content on Milling Characteristics in Two Rice Varieties

Drying conditions and grain moisture content (MC) before milling are important factors that influence rice milling quality and economic value. Two Egyptian rice cultivars, Sakha 108 and Egyptian Yasmine, as short and long grains, respectively were used in hot-air drying experiments in two successive growing seasons. In the present study, three initial grain moisture-content (MC) levels were evaluated for each cultivar. For Sakha 108, the first, second, and third initial average MC levels were 29.89 ± 0.30%w.b, 23.03 ± 0.14%w.b, and 20.37 ± 0.19%w.b, respectively. The corresponding values for Egyptian Yasmine were 30.57 ± 0.85%w.b, 23.12 ± 1.11%w.b, and 20.05 ± 0.74%w.b, respectively of rough rice, and were dried in three hot-air treatments at temperatures of 50 °C, 60 °C, and 70 °C to a final MC suitable for milling, around 14%w.b. After drying, we analyzed some milling-quality parameters, including husk percentage, brown rice percentage, bran and germ percentage, total milled rice percentage, broken rice percentage, and head rice yield percentage. Multiple-factor effect analysis found that the milling-quality parameters significantly differed as impacted by cultivar types, growing seasons, and initial grain moisture, while hot-air drying temperature only had significant effect on the head rice and broken rice percentage. The highest average percentage for head rice was produced by Sakha 108 (64.31%), with a mean of 55.71 ± 6.12%, while Egyptian Yasmine was only 55.05%, with mean of 44.40 ± 7.58%, during the first growing season. Reducing the initial grain MC from 29.89%w.b to 20.37%w.b (a 31.86% reduction) could increase the head rice percentage by 21.68% for Sakha 108; similarly, the Egyptian Yasmine head rice percentage could be increased by 43.59% by reducing the initial grain MC from 30.57%w.b to 20.37%w.b (a 34.41% reduction). The results provide useful information with the aim of improving the rice milling quality of Egyptian rice cultivars. This work combined initial grain moisture and hot-air drying temperatures to evaluate rice milling-quality variables with different rice cultivar kernel morphologies. This integrated comparison framework provides both practical drying assistance and essential data for rice-processing activities.