Abstract: This study attempted to establish the optimal conditions for three-stage drying of paddy. Hot air temperature at stage Ⅰ, moisture content at the end of stage Ⅰ, holding time at stage Ⅱ and hot air temperature at stage Ⅲ were selected as independent variables. In the first step, the ranges of the variables were determined by one-factor-at-a-time method for optimization. Subsequently, a mathematical model was developed for comprehensive evaluation of the drying characteristics of paddy using principal component analysis (PCA). Finally, optimization experiments were carried out based on the comprehensive evaluation using response surface methodology. As a result, the optimal drying conditions were determined as follows: air temperature at stage Ⅰ, 76.30 ℃; moisture content at the end of stage Ⅰ, 19.99%; holding time at stage Ⅱ, 11.34 d; and hot air temperature at stage Ⅲ, 35.53 ℃. Under these conditions, the composite score (F) was 1.284 with a cracking rate of 51% and a head rice rate of 64%, and the average drying rate was calculated to be 1.21%/h.

Key words: paddy, three-stage drying, principal component analysis, response surface methodology