Spatial Moisture Heterogeneity in Pressure Induction‐Heating Rice Cookers: Quantitative Analysis and the Effect of Stirring

ABSTRACT

Rice ( Oryza sativa L .) is a major staple food consumed worldwide and is typically eaten after starch gelatinization during cooking. Consequently, the degree of gelatinization state and the three‐dimensional distribution of moisture immediately after cooking are greatly affected by the cooking conditions. Although induction‐heating (IH) rice cookers are widely used, post‐cooking spatial moisture distribution remains insufficiently quantified. Hence, in this study, we aimed to investigate the spatial moisture distribution of rice cooked in an IH rice cooker and the effects of manual stirring. Pre‐washed rice was cooked under standardized conditions, and moisture content was measured across six sections. Without stirring, the outer‐lower section showed the highest moisture content (64.809% ± 3.094%), whereas the inner‐upper section exhibited the lowest (61.514% ± 2.610%). Immediate manual stirring after cooking homogenized the moisture distribution and significantly reduced the variability index (coefficient of variation) from 4.304% to 1.209% ( p  < 0.001). The accumulation of moisture in the lower region of the rice cooker may be attributed to non‐uniform heat transfer and moisture redistribution during cooking. Furthermore, starch gelatinization level varied among the rice portions, with the inner‐lower region (255.7 ± 11.4 mg/dL) showing the highest level and the outer‐upper region (156.8 ± 9.1 mg/dL) showing the lowest. A positive correlation was also observed between moisture content and starch gelatinization level (Spearman's ρ  = 0.77, p  < 0.01). These results illustrate the effectiveness of stirring in homogenizing rice moisture and may provide insights for optimizing cooking procedures and rice cooker design.