Buckwheat

G Mazza. Cambridge World History of Food. Editor: Kenneth F Kiple & Kriemhild Conee Ornelas. Volume 1. Cambridge, UK: Cambridge University Press, 2000.

Buckwheat (Fagopyrum esculentum Möench) is a crop commonly grown for its black or gray triangular seeds. It can also be grown as a green manure crop, a companion crop, a cover crop, as a source of buckwheat honey (often for the benefit of bees), and as a pharmaceutical plant yielding rutin, which is used in the treatment of capillary fragility. Buckwheat belongs to the Polygonaceae family (as do sorrel and rhubarb). Whereas cereals such as wheat, maize, and rice belong to the grass family, buckwheat is not a true cereal. Its grain is a dry fruit.

Buckwheat is believed to be native to Manchuria and Siberia and, reportedly, was cultivated in China by at least 1000 B.C. However, fragments of the grain have been recovered from Japanese sites dating from between 3500 and 5000 B.C., suggesting a much earlier date for the grain’s cultivation. It was an important crop in Japan and reached Europe through Turkey and Russia during the fourteenth and fifteenth centuries A.D., although legend would have it entering Europe much earlier with the returning Crusaders. Buckwheat was introduced into North America in the seventeenth century by the Dutch, and it is said that its name derives from the Dutch word bochweit (meaning “beech wheat”), because the plant’s triangular fruits resemble beechnuts. In German the name for beech is Buche, and for buckwheat, Buchweizen. Buckwheat has a nutty flavor and, when roasted (kasha), a very strong one. It is a hardy plant that grew in Europe where other grains did not and, thus, supplied peasants in such areas with porridge and pancakes.

Production of buckwheat peaked in the early nineteenth century and has declined since then. During the past decade or so, world production has averaged about 1 million metric tons annually, with the countries of the former Soviet Union accounting for about 90 percent of the total. Other major producing countries are China, Japan, Poland, Canada, Brazil, the United States, South Africa, and Australia. The yield of buckwheat varies considerably by area and by year of production and also with the variety being cultivated. In Canada, the average yield over the past 10 years has been about 800 kilograms per hectare (kg/ha), although yields of 2,000 kg/ha and higher have been produced.

Types and Cultivars

There are three known species of buckwheat: Common buckwheat (F. esculentum), tartary buckwheat (Fagopyrum tataricum), and perennial buckwheat (Fagopyrum cymosum). Common buckwheat is also known as Fagopyrum sagigtatum, and a form of tartary buckwheat may be called Fagopyrum kashmirianum. The cytotaxonomy of buckwheat has not been thoroughly studied, but it is generally believed that perennial buckwheat, particularly the diploid type, is the ancestral form of both tartary buckwheat and common buckwheat.

Tartary buckwheat (also known as rye buckwheat, duck wheat, hull-less, broomless, India wheat, Marino, mountain, Siberian, wild goose, and Calcutta buckwheat) is cultivated in the Himalayan regions of India and China, in eastern Canada, and, occasionally, in mountain areas of the eastern United States. Tartary buckwheat is very frost-resistant. Its seeds—and products made from them—are greenish in color and somewhat bitter in taste. Buckwheat is used primarily as an animal feed or in a mixture of wheat and buckwheat flour. It can also be used as a source of rutin.

Common buckwheat is by far the most economically important species of buckwheat, accounting for over 90 percent of world production. Many types, strains, and cultivars of common buckwheat exist—late-maturing and early-maturing types, Japanese and European types, summer and autumn types. Within a given type there may be strains or varieties with tall or short plants, gray or black seeds, and white or pink flowers. In general, however, common buckwheat varieties from different parts of the world may be divided into two major groups. The first group includes tall, vigorous, late-maturing, photoperiod-sensitive varieties, found in Japan, Korea, southern China, Nepal, and India. Members of the second group are generally insensitive to photoperiod and are small and early-maturing. All of the varieties in Europe and northern China belong to this second group.

Prior to 1950, most producers of buckwheat planted unnamed strains that had been harvested from their own fields or obtained from their neighbors or local stores. Named varieties, developed through plant breeding, were first made available in the 1950s. ‘Tokyo’, the oldest of the named cultivars introduced into North America, was licensed in 1955 by the Agriculture Canada Research Station in Ottawa. Other cultivars licensed for production in Canada are ‘Tempest’, ‘Mancan’, and ‘Manor’, all developed at the Agriculture Canada Research Station in Morden, Manitoba, since 1965. ‘Mancan’, which has large, dark-brown seeds, thick stems, and large leaves, is the Canadian cultivar preferred in the Japanese market because of its large seeds, desirable flavor and color, and high yield of groats in the milling process.

Cultivars licensed in the United States are ‘Penn-quad’ (released by the Pennsylvania Agricultural Experimental Station and the U.S. Department of Agriculture [USDA] in 1968) and ‘Giant American’ (a Japanese-type cultivar, apparently developed by a Minnesota farmer). Cultivars developed in the countries of the former Soviet Union since the 1950s include ‘Victoria’, ‘Galleya’, ‘Eneida’, ‘Podolyaka’, ‘Diadema’, ‘Aelita’, and ‘Aestoria’. Representative cultivars from other areas of the world include the following: ‘Pulawska’, ‘Emka’, and ‘Hruszowska’ from Poland; ‘Bednja 4n’ from Yugoslavia; and ‘Botan-Soba’,’Shinano No. 1′, ‘Kyushu-Akisoba Shinshu’, and ‘Miyazaki Oosoba’ from Japan.

Plant and Seed Morphology

Buckwheat is a broad-leaved, erect, herbaceous plant that grows to a height of 0.7 to 1.5 meters. It has a main stem and several branches and can reach full maturity in 60 to 110 days. The stem is usually grooved, succulent, and hollow, except for the nodes. Before maturity, the stems and branches are green to red in color; after maturity, however, they become brown. The plant has a shallow taproot from which branched, lateral roots arise. Its root system is less extensive than those of cereals and constitutes only 3 to 4 percent of the dry weight of the total plant, which—in conjunction with the large leaf surface—may cause wilting during periods of hot and dry weather.

Buckwheat has an indeterminate flowering habit. The flowers of common buckwheat are perfect but incomplete. They have no petals, but the calyx is composed of five petal-like sepals that are usually white, but may also be pink or red. The flowers are arranged in dense clusters at the ends of the branches or on short pedicels arising from the axils of the leaves. Common buckwheat plants bear one of two types of flowers. The pin-type flower has long styles (or female parts) and short stamens (or male parts), and the thrum-type flower has long styles and short pistils. The pistil consists of a one-celled superior ovary and a three-part style with knoblike stigmas and is surrounded by eight stamens. Nectar-secreting glands are located at the base of the ovary. The plants of common buckwheat are generally self-infertile, as self-fertilization is prevented by self-incompatibility of the dimorphic, sporophitic type. Seed production is usually dependent on cross-pollination between the pin and thrum flowers. Honeybees and leaf-cutter bees are effective pollinators that increase seed set and seed yield.

Plants of tartary buckwheat are significantly different from those of common buckwheat. They have only one flower type and are self-fertile. In addition, they tend to be more husky and more branched and to have narrower, arrow-shaped leaves and smaller, greenish-white flowers. Attempts to transfer the self-compatibility of tartary buckwheat to common buckwheat have proved unsuccessful.

The buckwheat kernel is a triangular, dry fruit (achene), 4 to 9 millimeters (mm) in length, consisting of a hull or pericarp, spermoderm, endosperm, and embryo. Large seeds tend to be concave-sided and small seeds are usually convex-sided. The hull may be glossy, gray, brown, or black and may be solid or mottled. It may be either smooth or rough with lateral furrows. The hulls represent 17 to 26 percent (in tartary buckwheat, 30 to 35 percent) of the kernel weight. Diploid varieties usually have less hull than tetraploids.

Structure of the Kernel

Scanning electron microscopy of the buckwheat kernel has revealed that the hull, spermoderm, endosperm, and embryo are each composed of several layers. For the hull, these are (in order from the outside toward the inside) the epicarp, fiber layers, parenchyma cells, and endocarp.The spermoderm is composed of the outer epiderm, the spongy parenchyma, and the inner epiderm. The endosperm includes an aleurone layer and a subaleurone endosperm, containing starch granules surrounded by a proteinaceous matrix. The embryo, with its two cotyledons, extends through the starchy endosperm.The terminal parts of the cotyledons are often parallel under the kernel surface.

Carbohydrates

Starch is quantitatively the major component of buckwheat seed, and concentration varies with the method of extraction and between cultivars. In the whole grain of common buckwheat, the starch content ranges from 59 to 70 percent of the dry matter. The chemical composition of starch isolated from buckwheat grains differs from the composition of cereal starches. The differences are most pronounced in the case of buckwheat and barley. The amylose content in buckwheat granules varies from 15 to 52 percent, and its degree of polymerization varies from 12 to 45 glucose units. Buckwheat starch granules are irregular, with noticeable f lat areas due to compact packing in the endosperm.

Buckwheat grains also contain 0.65 to 0.76 percent reducing sugars, 0.79 to 1.16 percent oligosaccharides, and 0.1 to 0.2 percent nonstarchy polysaccharides. Among the low-molecular-weight sugars, the major component is sucrose. There is also a small amount of arabinose, xylose, glucose, and, probably, the disaccharide melibiose.

Proteins

Protein content in buckwheat varies from 7 to 21 percent, depending on variety and environmental factors during growth. Most currently grown cultivars yield seeds with 11 to 15 percent protein. The major protein fractions are globulins, which represent almost half of all proteins and consist of 12 to 13 subunits with molecular weights between 17,800 and 57,000. Other known buckwheat protein fractions include albumins and prolamins. Reports of the presence of gluten or glutelin in buckwheat seed have recently been discredited.

Buckwheat proteins are particularly rich in the amino acid lysine. They contain less glutamic acid and proline and more arginine, aspartic acid, and tryptophan than do cereal proteins. Because of the high lysine content, buckwheat proteins have a higher biological value (BV) than cereal proteins such as those of wheat, barley, rye, and maize. Digestibility of buckwheat protein, however, is rather low; this is probably caused by the high-fiber content (17.8 percent) of buckwheat, which may, however, be desirable in some parts of the world. Buckwheat fiber is free of phytic acid and is partially soluble.

Lipids

Whole buckwheat seeds contain 1.5 to 3.7 percent total lipids. The highest concentration is in the embryo (7 to 14 percent) and the lowest in the hull (0.4 to 0.9 percent). However, because the embryo constitutes only 15 to 20 percent of the seed, and the hull is removed prior to milling, the lipid content of the groats is most meaningful. Groats (or dehulled seeds) of ‘Mancan’, ‘Tokyo’, and ‘Manor’ buckwheat contain 2.1 to 2.6 percent total lipids, of which 81 to 85 percent are neutral lipids, 8 to 11 percent phospholipids, and 3 to 5 percent glycolipids. Free lipids, extracted in petroleum ether, range from 2.0 to 2.7 percent. The major fatty acids of buckwheat lipids are palmitic (16:0), oleic (18:1), linoleic (18:2), stearic (18:0), linolenic (18:3), arachidic (20:0), behenic (22:0), and lignoceric (24:0). Of these, the first five are commonly found in all cereals, but the latter three, which represent, on average, 8 percent of the total acids in buckwheat, are only minor components or are not present in cereals.

Phenolic Compounds

The content of phenolics in hulls and groats of common buckwheat is 0.73 and 0.79 percent (and that of tartar y buckwheat, 1.87 and 1.52 percent). The three major classes of phenolics are flavonoids, phenolic acids, and condensed tannins. There are many types of flavonoids, three of which are found in buckwheat. These are flavonols, anthocyanins, and C-glycosylflavones. Rutin (quercetin 3-rutinoside), a well-known flavonol diglucoside, used as a drug for the treatment of vascular disorders caused by abnormally fragile or permeable capillaries, occurs in the leaves, stems, flowers, and fruit of buckwheat.

Grading, Handling, and Storage

Grading

In most countries, buckwheat grain is priced according to its physical condition in terms of size, soundness, and general appearance. In Canada, buckwheat is marketed according to grades established under the Canada Grain Act: Grades are No. 1, No. 2, and No. 3 Canada, and Sample. Grade determinants are a minimum test weight of 58 and 55 kilograms per hectoliter (kg/hL) (for Nos. 1 and 2 Canada), variety (designated by size, large or small), degree of soundness, and content of foreign material. Grades No. 1 and 2 Canada must be free from objectionable odors; No. 3 Canada may have a ground or grassy odor but may not be musty or sour. Test weight, seed size, and foreign material content are determined on a dockage-free sample. Seed size is determined with a No. 8 slotted sieve (3.18 • 19.05 mm) and becomes part of the grade name (e.g., “buckwheat, No. 1 Canada, large”).

“Foreign material” refers to cereal grains (wheat, rye, barley, oats, and triticale), weed seeds, and other grains that are not readily removable by mechanical cleaners, and may include peas, beans, maize, and other domestic or wild weeds. Buckwheat grain containing more than 5 percent foreign material is graded “buckwheat, Sample Canada, (size), account admixture.” Damaged seeds include frosted, moldy, distinctly green or otherwise unsound, and dehulled seeds.

In the United States, buckwheat is not marketed under federally established grades, but some states (for example, Minnesota) have official grain standards that specify the use of Grades 1, 2, 3, and Sample. The grade determinants are similar to those of the Canadian grading system. In Japan, the Buckwheat Millers Association prefers buckwheat that has large, uniform seeds with black hulls and green-colored groats.

Handling

Marketing of buckwheat can be more seriously affected by handling and storage than by other factors such as nutritional quality or processing. The method of handling varies among production areas; nonetheless, in most cases, losses and grain-quality changes occur at postharvest stages. During harvest, in all countries, losses occur, resulting from shattering, germination, depredation by animals, and infection by molds. Threshing is done with combines or by beating the dried plants against stones or wooden bars or by trampling the plants under bullock feet, carts, or tractor wheels.

Transportation of grain from the field to market also results in losses and quality deterioration. Losses during transportation are mainly due to spillage. However, if the grain is exposed to rain or frost during transit, it can subsequently spoil through infection by microorganisms. An efficient system for transportation and distribution of grain must consist of several components, including: (1) collection of grain from farms into consolidated deposits; (2) facilities for short- and long-term storage; (3) loading, unloading, and conveying systems; (4) methods of packaging or bulk handling; (5) roads, railways, and/or waterways; (6) systems for grading the grain and for servicing and maintaining equipment and facilities; (7) systems for recruiting, training, and managing personnel for operation and administration; and (8) systems for research, education, and extension of information to farmers, merchants, and other personnel involved with the overall handling operation.

Storage

Like other grain crops, buckwheat is stored to ensure an even supply over time, to preserve the surplus grain for sale to deficit areas, and for use as seed in the next planting season. Storage of the seeds may be at the farm, trader, market, government, retail, or consumer levels. Storage containers range from sacks to straw huts to bulk storage bins. In developing countries, traditional storage structures include granaries of gunny, cotton, or jute bags as well as those manufactured from reed, bamboo, or wood and plastered with mud and cow dung. In North America, storage structures include metal, concrete, or wooden bins at the farm level, elevators and annexes at centralized receiving, storage, and shipping points, and concrete silos at grain terminals.

Bagged buckwheat is highly susceptible to attack by insects and rodents. Hence, bulk storage in bins, elevators, and silos is best. Grain bins made of wood are usually square and, by virtue of their construction, possess a multitude of cracks, crevices, and angles that are havens for insects and their eggs and larvae. Concrete bins are usually round, star-shaped, or hexagonal, and star-shaped bins also have crevices that can harbor grain residues, constituting a source of infestation. Moreover, concrete possesses certain sorptive properties and chemical reactivity, and unless coated with an impervious material such as paint, the walls of concrete bins can interfere with fumigation procedures. Metal bins are usually round, possess few crevices, and do not react significantly with protective chemicals.

Neither concrete nor metal allows interchanges between stored grain and the atmosphere; moisture movement resulting from temperature fluctuations, convection, and condensation can result in deterioration and even internal combustion of the grains. A moisture content of 16 percent or less is required for the safe storage of buckwheat. If the seed requires drying, the temperature of the drying air should not exceed 43°C.

During storage at ambient temperature and relative humidity, the color of the aleurone layer changes from a desirable light green to the undesirable reddish brown. This undesirable quality change can be reduced by storing the seed at a lower temperature and at a relative humidity below 45 percent. Table II.A.3.6 gives the absorbance of the extracted color of buckwheat samples stored at 25°C and 0.11 to 0.67 water activity for 19 months. Maximum browning-pigment production occurs at 0.45 to 0.55 water activity, or 45 to 55 percent relative humidity.

Primary Processing

Primary processing of buckwheat includes cleaning, dehulling, and milling. The aim of seed cleaning is to remove other plant parts, soil, stones, weed seeds, chaff, dust, seeds of other crops, metallic particles, and small and immature buckwheat seeds. The extent and sophistication of the cleaning equipment depends largely on the size of the operation and the requirements for the finished product(s). Milling of buckwheat seed can be carried out by virtually any equipment capable of milling cereal grains. Hammer mills, stone mills, pin mills, disk mills, and roller mills have all been used to mill buckwheat. Of these, stone mills and roller mills are probably the most extensively used today.

The milling process may be of two types. In the first and most common type, the whole seeds are first dehulled and then milled. In the second type, the seeds are milled and then screened to remove the hulls. When dehulling and milling are separate operations, the seeds are segregated according to size and may be steamed and dried prior to dehulling. The latter procedure is carried out by impact or abrasion against emery stones or steel, followed by air- or screen-separation of groats and hulls. A widely used buckwheat dehuller is built on the principle of stone-milling, with emery stones set to crack the hull without breaking the groat. The effectiveness of this type of dehuller depends on the clearance between the seed cracking surfaces, and for any seed size there is an optimal setting. The ease of dehulling and the percentage of recovery of undamaged groats depends on variety and moisture content. From the dehuller, the groats go over sieves of different mesh for sizing into whole groats and two or more sizes of broken groats. Flour is produced by passing the groats through stone and/or roller grinders.

When buckwheat seed is to be processed into flour only, and production of groats is not a requirement, the seeds are ground on break rolls or stone mills and then screened to separate the coarse flour from the hulls. The coarse flour is further reduced by a series of size reduction rolls, each grinding operation followed by a sifting to fractionate the mixture of particles according to their size (Figure II.A.3.1). The flour yield ranges from 50 to 75 percent depending on the size, shape, and condition of the seeds and the efficiency of the dehulling and milling operations.

End Products

Buckwheat flour is generally dark in color because of the presence of hull fragments. In North America, it is used primarily for making buckwheat pancakes and is commonly marketed in the form of prepared mixes. These mixes generally contain buckwheat flour mixed with wheat, maize, rice, oat, or soybean flours and a leavening agent. Buckwheat is also used with vegetables and spices in kasha and soup mixes, and with wheat, maize, or rice in ready-to-eat breakfast products, porridge, bread, and pasta products.

In Japan, buckwheat flour is used primarily for making soba or sobakiri (buckwheat noodles) and Teuchi Soba(handmade buckwheat noodles). These products are prepared at soba shops or at home from a mixture of buckwheat and wheat flours. The wheat flour is used because of its binding properties and availability. Soba is made by hand or mechanically. In both methods, buckwheat and wheat flours are mixed with each other and then with water to form a stiff dough that is kneaded, rolled into a thin sheet (1.4 mm) with a rolling pin or by passing it between sheeting rolls, and cut into long strips. The product may be cooked immediately, sold fresh, or dried. For consumption, the noodles are boiled in hot water, put into bamboo baskets, and then dipped into cold water.

In Europe, most buckwheat is milled into groats that are used in porridge, in meat products (especially hamburger), or consumed with fresh or sour milk. A mixture of buckwheat groats with cottage cheese, sugar, peppermint, and eggs is employed as stuffing in a variety of dumplings. Buckwheat flour is used with wheat or rye flour and yeast to make fried specialty products such as bread, biscuits, and other confectioneries. An extended ready-to-eat breakfast product of high nutritional value, made from maize and buckwheat, is produced and marketed in Western Europe. This product contains over 14 percent protein and 8 percent soluble fiber. Similar products have also been developed in Poland and the former Soviet Union. In most countries, the quality of buckwheat end products is controlled by law.

The pace of development of new food products from buckwheat is expected to increase. This will likely parallel the increasing consumer demand for foods capable of preventing or alleviating disease and promoting health.