Rough rice stress fissuring with respect to conditions of drying and tempering processes

In this study the efficacy of intermittent and continuous drying processes on fissuring of Hashemi and Koohsar varieties was investigated. The fissuring of the kernels was assessed based on stress cracking index (SCI). The experiments were carried out at drying and tempering temperatures of 30, 45 and 60 °C, drying durations of 20, 40 and 60 min, and constant tempering duration of 80 min. In comparison with continuous drying method, under intermittent drying method, SCI value reduced significantly from 43.5 to 17, 74.5 to 28.3, and 83 to 58.4, respectively at temperatures of 30, 45 and 60 °C. Also, the value of SCI measured 48 h after finishing the drying process compared with its corresponding value measured immediately after drying operation increased significantly from 28.72 to 46.73. Both the total operation time (sum of all passes durations) and SCI decreased as tempering temperature increased due to the faster elimination of moisture gradients inside the kernels. Therefore, by appropriate tempering operation, besides maintaining the quality of the final product the total operation time could be reduced.