The properties of rice cooked in ion-exchanged water (2.5 mg/L of Ca2+ and 36.2 mg/L of Na+) and in tap water (15.7 mg/L of Ca2+ and 15.7 mg/L of Na+) were compared to clarify the effect of ion exchange by a domestic water- softener. The respective water content and rate of volume increase of the rice cooked in ion-exchanged water (ion-exchanged water rice) were 64.12% and 4.03-fold. These are significantly higher than the respective values of 62.03% and 3.83-fold for the rice cooked in tap water (tap water rice). The hardness of ion-exchanged water rice was significantly lower than that of tap water rice. The sensory evaluation judged the ion-exchanged water rice to be significantly softer and sweeter than the tap water rice. These results show that the water absorption and volume increase of rice were facilitated by cooking in ion-exchanged water from which Ca has been removed by the water- softener, giving softer rice. Scanning electron micrographs show starch granules on the surface of tap water rice, but not on ion-exchanged water rice.
