We analyzed the generation of defective gomu-mame (gummy beans) and ishi-mame (stone-formed beans) in boiled adzuki beans. As the number of days during which the adzuki beans are treated at a constant temperature (60℃) is increased, the moisture content of the raw beans is lost, leading to the increased generation of gomu-mame and ishi-mame. The abundance ratios of normal beans, gomu-mame, and ishi-mame 7 days post drying were 59.7%, 28.0%, and 12.3%, respectively. The coefficients of water absorption of boiled beans were 139.2% for normal beans, 60.8% for gomu-mame, and 0% for ishi-mame, with even less water being absorbed with harder boiled beans. The results of boiled bean tissues showed that starch grains swell in the surface and inner layers of normal beans but do not swell in the surface layer of gomu-mame, which had slightly swelled starch grains in the inner layer. In contrast, starch grains did not swell at all in ishi-mame. This suggests that the hard beans in boiled beans may reduce the quality of beans by changing bean nodules via over-drying, leading to substantially lower water absorption, which prevents water from reaching starch grains.
