Improved indices for dimensional classification of rice.

Criteria for classification of rice grains into shape/size types were studied. The dimensions length (L, mm), breadth (B, mm) and wt. (w, mg) were measured for 6 rice var. of similar grain shape but differing grain wt. and for 6 var. of similar grain wt. but different shape, and the usefulness of the following criteria for classification was studied: 3 parameters estimating surface area per unit wt., calculated to different levels of approximation; 10 x w/L, wB/L and wB. Results are tabulated. The best estimates of surface area/unit wt. were useful for classification, but these are too complex for use in routine practice, and more approximate values were less reliable; 10 x w/L (normalized grain wt. = wt. (mg)/cm) gave values useful for shape classification, and wt. and length are the easiest of the characters to measure. wB/L and wB also provided useful classification indices. Dimensions of 16 rice var. and values of classification indices are tabulated, together with amylose contents and water uptake values. Surface area/unit wt., 10 w/L, wB/L, wB, w and B were all correlated with water uptake, but L, L/B (used in some classification schemes) and contents of total or insoluble amylose were not significantly related to water uptake. The index 10 w/L is recommended as the simplest and most accurate for classification of rice fineness.