Common wheat or Bread wheat (T. aestivum) – A hexaploid species that is the most widely cultivated in the world.
Durum (T. durum) – The only tetraploid form of wheat widely used today, and the second most widely cultivated wheat.
Einkorn (T. monococcum) – A diploid species with wild and cultivated variants. Domesticated at the same time as emmer wheat, but never reached the same importance.
Emmer (T. dicoccum) – A tetraploid species, cultivated in ancient times but no longer in widespread use.
Spelt (T. spelta) – Another hexaploid species cultivated in limited quantities.
Classes used in the United States are:
Durum – Very hard, translucent, light-colored grain used to make semolina flour for pasta and bulghur.
Hard Red Spring – Hard, brownish, high-protein wheat used for bread and hard baked goods. Bread Flour and high-gluten flours are commonly made from hard red spring wheat. It is primarily traded at the Minneapolis Grain Exchange.
Hard Red Winter – Hard, brownish, mellow high-protein wheat used for bread, hard baked goods and as an adjunct in other flours to increase protein in pastry flour for pie crusts. Some brands of unbleached all-purpose flours are commonly made from hard red winter wheat alone. It is primarily traded by the Kansas City Board of Trade. One variety is known as “turkey red wheat”, and was brought to Kansas by Mennonite immigrants from Russia.
Soft Red Winter – Soft, low-protein wheat used for cakes, pie crusts, biscuits, and muffins. Cake flour, pastry flour, and some self-rising flours with baking powder and salt added, for example, are made from soft red winter wheat. It is primarily traded by the Chicago Board of Trade.
Hard White – Hard, light-colored, opaque, chalky, medium-protein wheat planted in dry, temperate areas. Used for bread and brewing.
Soft White – Soft, light-colored, very low protein wheat grown in temperate moist areas. Used for pie crusts and pastry. Pastry flour, for example, is sometimes made from soft white winter wheat.
Red wheat may need bleaching; therefore, white wheat usually command higher prices than red wheat on the commodities market.
Hulled versus free-threshing wheat
The four wild species of wheat, along with the domesticated varieties einkorn, emmer and spelt, have hulls. This more primitive morphology (in evolutionary terms) consists of toughened glumes that tightly enclose the grains, and (in domesticated wheats) a semi-brittle rachis that breaks easily on threshing. The result is that when threshed, the wheat ear breaks up into spikelets. To obtain the grain, further processing, such as milling or pounding, is needed to remove the hulls or husks. In contrast, in free-threshing (or naked) forms such as durum wheat and common wheat, the glumes are fragile and the rachis tough. On threshing, the chaff breaks up, releasing the grains. Hulled wheats are often stored as spikelets because the toughened glumes give good protection against pests of stored grain.
Naming
There are many botanical classification systems used for wheat species, discussed in a separate article on Wheat taxonomy. The name of a wheat species from one information source may not be the name of a wheat species in another.
Within a species, wheat cultivars are further classified by wheat breeders and farmers in terms of:
- Growing season, such as winter wheat vs. spring wheat, by gluten content, such as hard wheat (high protein content) vs. soft wheat (high starch content), or by grain color (red, white or amber).
- Protein content. Bread wheat protein content ranges from 10% in some soft wheat with high starch contents, to 15% in hard wheat.
- The quality of the wheat protein gluten. This protein can determine the suitability of a wheat to a particular dish. A strong and elastic gluten present in bread wheat enables dough to trap carbon dioxide during leavening, but elastic gluten interferes with the rolling of pasta into thin sheets. The gluten protein in durum wheat used for pasta is strong but not elastic.
- Grain color (red, white or amber). Many wheat varieties are reddish-brown due to phenolic compounds present in the bran layer which are transformed to pigments by browning enzymes. White wheat have a lower content of phenolics and browning enzymes, and are generally less astringent in taste than red wheat. The yellowish color of durum wheat and semolina flour made from it is due to a carotenoid pigment called lutein, which can be oxidized to a colorless form by enzymes present in the grain.
