Water uptake by rice during cooking

In 1961, 20 samples of rice, average moisture content 12.8%, milled to full polish in a commercial huller and in 1968-1969, samples, average moisture content 13.5%, milled by standard laboratory methods, were cooked in distilled water in a boiling water-bath, temp. 97.5 degree C, cooled in water for 1 min, spread over a wire screen, stirred over filter paper sheets for 3 sec and weighed. On cooking for a constant time of 20 min each, the 20 different rice varieties varied widely in their apparent water uptake (1.65-2.45 g/g). Water uptake by the rice was found to be primarily related to its surface area which is a function of size and shape. Small and slender varieties absorb more water at a given cooking time than do large and round varieties. Water uptake was generally unrelated to other physicochemical and quality characteristics, except for a small inverse relationship with protein content and gelatinization temp. It was also affected by cracks and abdominal white, by age and processing. All varieties cooked for their optimal times showed a relatively constant water uptake of approximate equal to2.5 and attained a moisture content of 75%. The best correlation is obtained when the value is expressed as a ratio of the water uptake at 70-80 degree C to that at boiling temp. thereby eliminating the interfering effects of surface area, cracked and chalky kernels, age and protein content.