Sizing Up Wheat Kernels

June, 1999

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When it comes to sizing up the wheat kernel, not all wheat varieties are created equal. We have all seen them—kernels of various sizes and shapes. There is no question genetics plays an important role in determining wheat kernel size, but the environment can also affect kernel size and the amount of variability in a given sample.

So why the big deal? Wheat buyers around the globe are taking physical characteristics of wheat more seriously now in making purchase decisions. Millers can make proper adjustments in their equipment and maximize flour yield if kernel size characteristics of wheat lots are known. Large wheat kernels produce higher flour yield than smaller ones, because the former contains more endosperm that millers can convert into flour. Certainly, wheat buyers would prefer larger kernels, as reflected in a large 1000-kernel weight, but also important is the uniformity in kernel size.

Precise and rapid determination of kernel size and variability is therefore more important than ever. A special instrument called the Single Kernel Characterization System (SKCS) makes that possible. It came into play in the mid-1990s, mainly for the purpose of classifying and grading hard vs. soft wheat. New wheat varieties released in the 1980s had hardness characteristics that made them difficult to classify visually. Thus, some samples were mis-classified as "mixed", imposing significant penalties on producers, although the samples were genetically from one class. (Remember the variety, Arkan?)

The SKCS has the capability of predicting many quality parameters, but four provide the mainstay of this instrument: kernel weight, diameter, hardness, and moisture. How does the SKCS work? It passes individual kernels (about 300 per sample) through a crushing device—a toothed rotor and progressively narrowing crescent-shaped gap—and measures the four characteristics and reports their values as an average for the sample and the "variance" (or dispersion) for that sample. The SKCS is becoming widely used in wheat breeding programs around the world to select breeding lines that produce large and uniform kernels.

The SKCS is one of several instruments used by the WIT to breed new varieties possessing desirable kernel characteristics, such as weight and size, along with other agronomic and quality attributes including test weight. Our goal is to develop new varieties that have improved market potential relative to physical kernel quality. Recent varieties released by OSU, such as Tonkawa, Custer, and 2174, are providing the necessary building blocks to achieve that goal. Future editions of this column will address other important factors of quality being addressed by the Wheat Improvement Team.