INNOVATIVE PADDY DRYING VIA MILD TORREFACTION UNDER CLOSED-LOOP GAS CIRCULATION SYSTEM

Abstract

This study investigated the effectiveness of mild torrefaction under a closed-loop gas circulation system for moisture reduction and moisture reabsorption behavior of paddy rice. Drying experiments were conducted at temperatures ranging from 40 to 80°C, drying times of 10–30 minutes, and feed rates of 500, 1,000, and 1,500 g. All experiments were performed in triplicate, and results were reported as mean ± standard deviation. The results demonstrated that drying temperature and residence time significantly affected moisture reduction efficiency. Higher temperatures enhanced the drying rate, while increasing feed rate slightly reduced drying efficiency due to increased resistance to heat and mass transfer within the material bed. Nevertheless, effective moisture reduction was achieved under all investigated conditions. In addition, paddy rice treated at 70–80°C with drying times longer than 20 minutes exhibited significantly reduced moisture reabsorption behavior, indicating improved moisture stability during storage. This behavior was attributed to structural modification within the grain under low-oxygen and closed-loop gas circulation conditions, which reduced the hygroscopic characteristics of the material. The findings suggest that mild torrefaction under a closed-loop gas circulation system has strong potential as an alternative drying technology for post-harvest paddy management. The process can improve drying efficiency, reduce moisture reabsorption, and support semi-industrial drying applications.