Microwave Drying Characteristics of Soybeans in Single and Variable Microwave Power Density

Drying characteristics of soybeans under different microwave (MW) processing schemes were studied in regard to energy aspects. For drying in a single microwave power density, the experiments were carried out at a constant MW output power throughout the process. It was found that the drying rate is enhanced together with reduced energy consumption at higher single power density, but the soybean cracking ratio is increased gradually from 2 % to 40 % when the power density was changed from 0.2 W/g to 0.8 W/g. Efforts were made to reach a compromise between the drying rate and dried soybean quality by varying the MW power density in several steps overall the drying process, but soybean cracking occurred at a higher ratio due to the fluctuation of drying rate. Microwave drying of soybeans under the power density less than 0.2 W/g with slow and stable drying rate can achieve the soybean cracking ratio controlled within 5 % and lower energy consumption.