Rice milling quality can be influenced by any factor that affects kernel strength, which is ultimately responsible for the kernel withstanding the processes of hulling and bran removal without breaking apart.

Rice milling yield is quantified by two numbers (for example: 58/70).  The number 70 in this example is themilled rice yield, which is determined by the amount of white rice remaining after the hulling and milling processes. It is calculated by dividing the mass of the milled rice by the original mass of the rough rice prior to processing, and typically ranges from 68 to 72 percent.

The number 58 in the example is thehead rice yield, and it is determined by the amount of milled rice kernels that are “whole.” Whole milled kernels remain three-fourths or more of their original length.

Head rice yield is calculated by dividing the mass of head rice by the original mass of rough rice. Head rice yield can vary from zero, meaning all kernels broken, to as high as the milled rice yield (as much as 68-72 percent with no kernels broken).

Milling quality is often expressed as a ratio of head rice yield to milled rice yield. For example, a 58/70 value would indicate a head rice yield of 58 percent, milled rice yield of 70 percent, and 12 percent broken kernels -- the difference between the two values.

Harvest moisture content may have the greatest effect on rice milling quality that is within a producer’s control. Head rice yield varies with the moisture content at which rice is harvested. Under typical Arkansas weather conditions the harvest moisture content at which head rice yield is maximum is approximately 19 to 21 percent for long-grain cultivars and 22 to 24 percent for medium-grains.

As rice matures, kernels on a panicle exist at very different moisture contents, representing various maturity and kernel strength levels. Some kernels are immature or “green,” with greater than 22 percent moisture. Others are “dry” kernels, with lower than 14 percent moisture.