High-Power Short Duration Microwave Drying of Rice Versus Fissuring and Milling Yields

Abstract

Highlights MW specific energy ranging from 422.5 to 507.0 kJ/kg of rice can dry rice to 12.5% moisture content in a single pass. Fissuring percentage was significantly lower for lower drying durations as compared to 3 min drying durations for all power levels. RR dried for one minute with MW at 16-20 kW results in higher head rice yields. Abstract. The utilization of microwave (MW) drying technology to dry rough rice (RR) is considered a promising method for high-moisture RR drying with high throughput. Milling quality is a significant factor in stakeholders adoption of this method. Therefore, experiments were conducted using an industrial MW dryer operating at 915 MHz to examine the effects of different MW power levels and heating durations on RR drying. Single pass drying was performed using 16, 18, and 20 kW power levels and 1, 2, and 3 min heating durations. A control sample was dried in an environmentally controlled chamber at 25°C and 56% relative humidity (RH). The moisture content, surface temperature, fissuring, and head rice yield (HRY) of RR were measured. The initial moisture content of RR was 21.22% w.b. The moisture content of RR after 3 minutes of drying at the studied power levels was close to the recommended rice milling moisture content of 13%, indicating the feasibility of single pass MW drying. The maximum surface temperature of RR at severe (20 kW for 3 min) and least severe (16 kW and 1 min) treatment conditions was 91.9°C and 62.6°C, respectively. Fissuring percentages of 86.2% and 85.3% were observed in RR drying at 20 kW for 3 min after one day and after seven days of fissure examination, respectively. Fissuring percentages of 84.2% and 84.3% were observed at 16 kW for 3 min drying after one day and after seven days, respectively. The HRY at MW drying conditions of 16-20 kW for 1 min was higher than that of RR gently dried at 25°C and 56% RH. MW drying shows promise for reducing drying duration compared to conventional methods. Keywords: Head rice yield, Microwave drying, Moisture content, Rice drying, Rice fissuring.