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Wheat

Plant Sciences

Wheat

Common wheat (Triticum aestivum ) is an annual cool season grass that is grown across a wide range of environments around the world. It has the broadest range of adaptation of all the cereals and more land is devoted to wheat than any other commercial crop. Wheat is the number-one food grain consumed directly by humans, and its production leads all crops, including rice, maize, and potatoes.

Wheat is a typical grass in that it forms several leafy shoots that grow about one meter in height. Each shoot has five to seven nodes and produces an inflorescence that is a thick condensed spike. Each spike has a main axis bearing spikelets separated by short internodes with two to five florets within each spikelet. Wheat normally has thirty to forty kernels per spike and is self-pollinated. The moisture content of the seed is about 10 percent, which makes wheat grain easy to store and transport.

This crop is the most important source of carbohydrates in the majority of countries in the temperate zone. Wheat is an excellent food, even though the grain is deficient in some essential amino acids (it is particularly low in lysine). Wheat starch is easily digested, as is most wheat protein. The grain contains minerals, vitamins, and fats (lipids), and when wheat products are complemented by small amounts of animal or legume protein, the combination is highly nutritious. A predominantly wheat-based diet is higher in fiber and lower in fats than a meat-based diet.

Most of the wheat marketed is used to manufacture flour from which bread, cakes, cookies, crackers, and pastries are made. Wheat grain is an excellent livestock feed, as are many of the by-products from the milling of the grain into flour. Normally about 70 percent of the grain can be made into flour and the rest into very useful by-products. Also, the green plants can be used for livestock forage.

Wheat has unique baking properties, the most important of which is the elasticity of its gluten protein. The amount and quality of the gluten produced by any particular type are prime factors in determining the quality of the flour that can be obtained from the milling process. Unlike any other grain or plant product, wheat gluten enables dough to rise through the formation of small gas cells that retain the carbon dioxide formed during yeast fermentation or chemical leavening. This is what gives bread its porous structure. Bread has been a basic food for humans throughout recorded history, and probably for a much longer period: it remains the principal food product made from wheat.

Wheat is divided into several classes based on the level of the gluten protein. Hard wheats are high in protein (13 to 15 percent) with strong gluten strength and are used primarily for bread making. Soft wheats are low in protein (10 to 12 percent) with weak gluten strength and are used for cakes, cookies, and other pastries.

There are also two types of wheat based on the season they are grown. Winter wheat is fall planted and is harvested in early summer. Spring wheat is planted in the early spring and harvested in the summer. Winter wheat is quite winter hardy and actually requires cold temperatures in order to head out and produce a grain crop, whereas spring wheat is not winter hardy and does not have a cold requirement to produce grain.

A crop of wheat is harvested somewhere in the world during every month of the year. Most of the global harvest, however, occurs between April and September in the temperate zone of the Northern Hemisphere; considerably less wheat is grown in the Southern Hemisphere, where harvest occurs from October to January.

The culture of wheat is highly mechanized with large grain drills used to plant and large combines to harvest. A single person can grow hundreds of acres since it is not labor intensive. Wheat does not require as much fertilizer as most other crops and only occasionally requires pesticides such as fungicides, herbicides, or insecticides. Wheat is less profitable on a per-acre basis than many other crops and to date no genetically transformed wheat has been grown on a commercial scale. A great deal of research is being done with wheat and it is probable that genetically engineered wheat will be available in the near future.

see also Agriculture, History of; Agriculture, Modern; Economic Importance of Plants; Grains; Transgenic Plants.

Ronald D. Barnett

Bibliography

Briggle, L. W. "Origin and Botany of Wheat." In Wheat, ed. E. Hafliger. Basel, Switzerland: Documenta Ciba-Geigy, 1980.

——, and B. C. Curtis. "Wheat Worldwide." In Wheat and Wheat Improvement, ed. E. G. Heyne. Madison, WI: American Society of Agronomy, Inc., 1987.

Buskuk, W., and C. W. Wrigley. "Proteins: Composition, Structure, and Function." In Wheat: Production and Utilization, ed. G. E. Inglett. Westport, CT: AVI Publishing Co., 1974.

Johnson, V. A., L. W. Briggle, J. D. Axtell, L. F. Bouman, E. R. Leng, and T. H. Johnston. "Grain Crops." In Protein Resources and Technology, eds. M. Milner et al. Westport, CT: AVI Publishing Co., 1978.

Leonard, W. H., and J. H. Martin. Cereal Crops. New York: Macmillan, 1963.

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