The value of milled rice in the market is determined by a number of physical and chemical characteristics and the consumers preference, which varies within a country and between the countries.
Milling degree or colour: The degree of milling or amount of the brown rice removed, affects the colour of white rice, and often the price. Under-milled rice absorbs water poorly, does not cook well, and is normally cheaper.
Head rice or broken percentage: Milled rice, having 75-80 % head rice (whole kernels), also includes broken kernels. High head rice yield is one of the most important criteria for measuring milled rice quality. High-quality rice normally has less than 5% broken grains.
Whiteness or translucency: This characteristic is a combination of varietal physical characteristics and the degree of milling. During milling, the whitening and polishing process greatly affects the whiteness of the grain and its transparency.
Chalkiness: Grain appearance is affected by the amount of chalkiness or white belly. Chalkiness is caused by interruption in the final grain-filling. Though chalkiness disappears upon cooking (and has no direct effect on cooking and eating qualities), excessive chalkiness often downgrades the quality and reduces milling recovery.
Gelatinization temperature or cooking time: Environmental conditions such as temperature during ripening influence gelatinization temperature. There is normally a preference for rice with intermediate gelatinization temperature.
Amylose content or stickiness: The amylose content of rice usually ranges from 15–35%. High-amylose rice has high volume-expansion, the grains cook dry, are less tender, and become hard upon cooling. Low-amylose rice cooks moist and sticky. Intermediate-amylose rice (21–24%) is preferred in most rice-growing areas of the world.
Gel consistency: Gel consistency measures the tendency of the cooked rice to harden on cooling. Varieties with a softer gel consistency are preferred if rice is to be consumed after cooling, or if cooked rice with higher degree of tenderness is desired.