Barley (Hordeum vulgare), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago.^[3] Barley has been used as animal fodder, as a source of fermentable material for beer and certain distilled beverages, and as a component of various health foods. It is used in soups and stews, and in barley bread of various cultures. Barley grains are commonly made into malt in a traditional and ancient method of preparation.

In 2017, barley was ranked fourth among grains in quantity produced (149 million tonnes) behind maize, rice and wheat.^[4]

The Old English word for barley was bere, which traces back to Proto-Indo-European and is cognate to the Latin word farina "flour".

The direct ancestor of modern English barley in Old English was the derived adjective bærlic, meaning "of barley".^[5] The first citation of the form bærlic in the Oxford English Dictionary dates to around 966 CE, in the compound word bærlic-croft.^[6]
The underived word bære survives in the north of Scotland as bere, and refers to a specific strain of six-row barley grown there.^[7]

The word barn, which originally meant "barley-house", is also rooted in these words.^[5]

The Latin word hordeum, used as barley's scientific genus name, is derived from an Indo-European root meaning "bristly" after the long prickly awns of the ear of grain.

Barley is a member of the grass family. It is a self-pollinating, diploid species with 14 chromosomes. The wild ancestor of domesticated barley, Hordeum vulgare subsp. spontaneum, is abundant in grasslands and woodlands throughout the Fertile Crescent area of Western Asia and northeast Africa, and is abundant in disturbed habitats, roadsides, and orchards. Outside this region, the wild barley is less common and is usually found in disturbed habitats.^[3] However, in a study of genome-wide diversity markers, Tibet was found to be an additional center of domestication of cultivated barley.^[8]

Wild barley (H. spontaneum) is the ancestor of domestic barley (H. vulgare). Over the course of domestication, barley grain morphology changed substantially, moving from an elongated shape to a more rounded spherical one.^[9] Additionally, wild barley has distinctive genes, alleles, and regulators with potential for resistance to abiotic or biotic stresses to cultivated barley and adaptation to climatic changes.^[10] Wild barley has a brittle spike; upon maturity, the spikelets separate, facilitating seed dispersal. Domesticated barley has nonshattering spikes, making it much easier to harvest the mature ears.^[3] The nonshattering condition is caused by a mutation in one of two tightly linked genes known as Bt1 and Bt2; many cultivars possess both mutations. The nonshattering condition is recessive, so varieties of barley that exhibit this condition are homozygous for the mutant allele.^[3]

Each plant gets a set of genes from both parents, so two copies of each gene are in every plant. If one gene copy is a nonworking mutant, but the other gene copy works, the mutation has no effect. Only when the plant is homozygous with both copies of the gene as nonworking mutants does the mutation show its effect by exhibiting the nonshattering condition.

Domestication in barley is followed by the change of key phenotypic traits at the genetic level. Little is known about the genetic variation among domesticated and wild genes in the chromosomal regions.^[11]

Spikelets are arranged in triplets which alternate along the rachis. In wild barley (and other Old World species of Hordeum), only the central spikelet is fertile, while the other two are reduced. This condition is retained in certain cultivars known as two-row barleys. A pair of mutations (one dominant, the other recessive) result in fertile lateral spikelets to produce six-row barleys.^[3] Recent genetic studies have revealed that a mutation in one gene, vrs1, is responsible for the transition from two-row to six-row barley.^[12]

Two-row barley has a lower protein content than six-row barley, thus a more fermentable sugar content. High-protein barley is best suited for animal feed. Malting barley is usually lower protein^[13] ("low grain nitrogen", usually produced without a late fertilizer application) which shows more uniform germination, needs shorter steeping, and has less protein in the extract that can make beer cloudy. Two-row barley is traditionally used in English ale-style beers, with two-row malted summer barley being preferred for traditional German beers.

Amylase-rich six-row barley is common in some American lager-style beers, especially when adjuncts such as corn and rice are used.

Hulless or "naked" barley (Hordeum vulgareL. var.nudum Hook. f.) is a form of domesticated barley with an easier-to-remove hull. Naked barley is an ancient food crop, but a new industry has developed around uses of selected hulless barley to increase the digestible energy of the grain, especially for swine and poultry.^[14] Hulless barley has been investigated for several potential new applications as whole grain, and for its value-added products. These include bran and flour for multiple food applications.^[15]

In traditional classifications of barley, these morphological differences have led to different forms of barley being classified as different species. Under these classifications, two-row barley with shattering spikes (wild barley) is classified as Hordeum spontaneum K. Koch. Two-row barley with nonshattering spikes is classified as H. distichum L., six-row barley with nonshattering spikes as H. vulgare L. (or H. hexastichum L.), and six-row with shattering spikes as H. agriocrithon Åberg.

Because these differences were driven by single-gene mutations, coupled with cytological and molecular evidence, most recent classifications treat these forms as a single species, H. vulgare L.^[3]

H. vulgare contains the phenolics caffeic acid and p-coumaric acid, the ferulic acid 8,5'-diferulic acid, the flavonoids catechin-7-O-glucoside,^[24] saponarin,^[25] catechin, procyanidin B3, procyanidin C2, and prodelphinidin B3, and the alkaloid hordenine.

Barley was one of the first domesticated grains in the Fertile Crescent, an area of relatively abundant water in Western Asia, and near the Nile river of northeast Africa.^[27] The grain appeared in the same time as einkorn and emmer wheat.^[28] Wild barley (H. vulgare ssp. spontaneum) ranges from North Africa and Crete in the west, to Tibet in the east.^[3] According to some scholars, the earliest evidence of wild barley in an archaeological context comes from the Epipaleolithic at Ohalo II at the southern end of the Sea of Galilee. The remains were dated to about 8500 BCE.^[3] Other scholars have written that the earliest evidence comes from Mesopotamia, specifically the Jarmo region of modern day Iraq.

One of the world's most important crops, barley, was domesticated in the Near East around 11,000 years ago (circa 9,000 BCE).^[26] Barley is a highly resilient crop, able to be grown in varied and marginal environments, such as in regions of high altitude and latitude.^[26] Archaeobotanical evidence shows that barley had spread throughout Eurasia by 2,000 BCE.^[26] To further elucidate the routes by which barley cultivation was spread through Eurasia, genetic analysis was used to determine genetic diversity and population structure in extant barley taxa.^[26] Genetic analysis shows that cultivated barley spread through Eurasia via several different routes, which were most likely separated in both time and space.^[26]

Some scholars believe domesticated barley (hordeum vulgare) originally spread from Central Asia to India, Persia, Mesopotamia, Syria and Egypt.^[29] Some of the earliest domesticated barley occurs at aceramic ("pre-pottery") Neolithic sites, in the Near East such as the Pre-Pottery Neolithic B layers of Tell Abu Hureyra, in Syria. By 4200 BCE domesticated barley occurs as far as in Eastern Finland^[30] and had reached Greece and Italy around the 4th c. BCE.^[29] Barley has been grown in the Korean Peninsula since the Early Mumun Pottery Period (circa 1500–850 BCE) along with other crops such as millet, wheat, and legumes.^[31]

Barley (known as Yava in both Vedic and Classical Sanskrit) is mentioned many times in Rigveda and other Indian scriptures as one of the principal grains in ancient India.^[32] Traces of Barley cultivation have also been found in post-Neolithic Bronze Age Harappan civilization 5700–3300 years before present.^[33]

In the Pulitzer Prize-winning book Guns, Germs, and Steel, Jared Diamond proposed that the availability of barley, along with other domesticable crops and animals, in southwestern Eurasia significantly contributed to the broad historical patterns that human history has followed over approximately the last 13,000 years; i.e., why Eurasian civilizations, as a whole, have survived and conquered others.^[34]

Barley beer was probably one of the first alcoholic drinks developed by Neolithic humans.^[35] Barley later on was used as currency.^[35] The ancient Sumerian word for barley was akiti. In ancient Mesopotamia, a stalk of barley was the primary symbol of the goddess Shala.^[36] Alongside emmer wheat, barley was a staple cereal of ancient Egypt, where it was used to make bread and beer. The general name for barley is jt (hypothetically pronounced "eat"); šma (hypothetically pronounced "SHE-ma") refers to Upper Egyptian barley and is a symbol of Upper Egypt. According to Deuteronomy 8:8, barley is one of the "Seven Species" of crops that characterize the fertility of the Promised Land of Canaan, and it has a prominent role in the Israelite sacrifices described in the Pentateuch (see e.g. Numbers 5:15). A religious importance extended into the Middle Ages in Europe, and saw barley's use in justice, via alphitomancy and the corsned.

Rations of barley for workers appear in Linear B tablets in Mycenaean contexts at Knossos and at Mycenaean Pylos.^[37] In mainland Greece, the ritual significance of barley possibly dates back to the earliest stages of the Eleusinian Mysteries. The preparatory kykeon or mixed drink of the initiates, prepared from barley and herbs, referred in the Homeric hymn to Demeter, whose name some scholars believe meant "Barley-mother".^[38] The practice was to dry the barley groats and roast them before preparing the porridge, according to Pliny the Elder's Natural History (xviii.72). This produces malt that soon ferments and becomes slightly alcoholic.

Pliny also noted barley was a special food of gladiators known as hordearii, "barley-eaters". However, by Roman times, he added that wheat had replaced barley as a staple.^[39]

Tibetan barley has been a staple food in Tibetan cuisine since the fifth century CE. This grain, along with a cool climate that permitted storage, produced a civilization that was able to raise great armies.^[40] It is made into a flour product called tsampa that is still a staple in Tibet.^[41] The flour is roasted and mixed with butter and butter tea to form a stiff dough that is eaten in small balls.

In medieval Europe, bread made from barley and rye was peasant food, while wheat products were consumed by the upper classes.^[39] Potatoes largely replaced barley in Eastern Europe in the 19th century.^[42]

The genome of barley was sequenced in 2012,^[43] due to the efforts of the International Barley Genome Sequencing Consortium and the UK Barley Sequencing Consortium.

The genome is composed of seven pairs of nuclear chromosomes (recommended designations: 1H, 2H, 3H, 4H, 5H, 6H and 7H), and one mitochondrial and one chloroplast chromosome, with a total of 5000 Mbp.^[44]

Abundant biological information is already freely available in several barley databases.^[45]

The wild barley (H. vulgare ssp.spontaneum) found currently in the Fertile Crescent might not be the progenitor of the barley cultivated in Eritrea and Ethiopia, indicating that separate domestication may have occurred in eastern Africa.^[46]

In 2017, world production of barley was 149 million tonnes, led by the Russia producing 14% of the world total. Australia, Germany, France, and Ukraine were major producers.^[4]

Barley is a widely adaptable crop. It is currently popular in temperate areas where it is grown as a summer crop and tropical areas where it is sown as a winter crop. Its germination time is one to three days. Barley grows under cool conditions, but is not particularly winter hardy.

Barley is more tolerant of soil salinity than wheat, which might explain the increase of barley cultivation in Mesopotamia from the second millennium BCE onwards. Barley is not as cold tolerant as the winter wheats (Triticum aestivum), fall rye (Secale cereale) or winter triticale (× Triticosecale Wittm. ex A. Camus.), but may be sown as a winter crop in warmer areas of Australia and Great Britain.

Barley has a short growing season and is also relatively drought tolerant.^[39]

Is known or likely to be susceptible to barley mild mosaic bymovirus,^[47][48] as well as bacterial blight. It can be susceptible to many diseases, but plant breeders have been working hard to incorporate resistance. The devastation caused by any one disease will depend upon the susceptibility of the variety being grown and the environmental conditions during disease development. Serious diseases of barley include powdery mildew caused by Blumeria graminis f.sp. hordei, leaf scald caused by Rhynchosporium secalis, barley rust caused by Puccinia hordei, crown rust caused by Puccinia coronata, and various diseases caused by Cochliobolus sativus. Barley is also susceptible to head blight.

In a 100-g serving, raw barley provides 352 Calories and is a rich source (20% or more of the Daily Value, DV) of essential nutrients, including protein, dietary fiber, the B vitamins, niacin (31% DV) and vitamin B6 (20% DV), and several dietary minerals (table). Highest nutrient contents are for manganese (63% DV) and phosphorus (32% DV) (table). Raw barley is 78% carbohydrates, 1% fat, 10% protein, and 10% water (table).

Hulled barley (or covered barley) is eaten after removing the inedible, fibrous, outer hull. Once removed, it is called dehulled barley (or pot barley or scotch barley).^[49] Considered a whole grain, dehulled barley still has its bran and germ, making it a nutritious and popular health food. Pearl barley (or pearled barley) is dehulled barley which has been steam processed further to remove the bran.^[49] It may be polished, a process known as "pearling". Dehulled or pearl barley may be processed into a variety of barley products, including flour, flakes similar to oatmeal, and grits.

Barley meal, a wholemeal barley flour lighter than wheat meal but darker in colour, is used in porridge and gruel in Scotland.^[49] Barley meal gruel is known as sawiq in the Arab world.^[50] With a long history of cultivation in the Middle East, barley is used in a wide range of traditional Arabic, Assyrian, Israelite, Kurdish, and Persian foodstuffs including kashkak, kashk and murri. Barley soup is traditionally eaten during Ramadan in Saudi Arabia.^[51] Cholent or hamin (in Hebrew) is a traditional Jewish stew often eaten on Sabbath, in a variety of recipes by both Mizrachi and Ashkenazi Jews, with barley cited throughout the Hebrew Bible in multiple references. In Eastern and Central Europe, barley is also used in soups and stews such as ričet. In Africa, where it is a traditional food plant, it has the potential to improve nutrition, boost food security, foster rural development and support sustainable landcare.^[52]

The six-row variety bere is cultivated in Orkney, Shetland, Caithness and the Western Isles in the Scottish Highlands and islands. When milled into beremeal it is used locally in bread, biscuits, and the traditional beremeal bannock.^[53]

According to Health Canada and the US Food and Drug Administration, consuming at least 3 grams per day of barley beta-glucan or 0.75 grams per serving of soluble fiber can lower levels of blood cholesterol, a risk factor for cardiovascular diseases.^[54][55]

Eating whole-grain barley, as well as other grains with lots of fiber, improves regulation of blood sugar (i.e., reduces blood glucose response to a meal).^[56] Consuming breakfast cereals containing barley over weeks to months also improved cholesterol levels and glucose regulation.^[57]

Like wheat, rye, and their hybrids and derivatives, barley contains gluten, which makes it an unsuitable grain for consumption by people with gluten-related disorders, such as celiac disease, non-celiac gluten sensitivity and wheat allergy sufferers, among others.^[58] Nevertheless, some wheat allergy patients can tolerate barley or rye.^[59]

Barley is a key ingredient in beer and whisky production. Two-row barley is traditionally used in German and English beers. Six-row barley was traditionally used in US beers, but both varieties are in common usage now.^[60] Distilled from green beer,^[61] whiskey has been made primarily from barley in Ireland and Scotland, while other countries have used more diverse sources of alcohol, such as the more common corn, rye and wheat in the USA. In the US, a grain type may be identified on a whisky label if that type of grain constitutes 51% or more of the ingredients and certain other conditions are satisfied.^[62] About 25% of the United States' production of barley is used for malting, for which barley is the best-suited grain.^[63]

Barley wine is a style of strong beer from the English brewing tradition. Another alcoholic drink known by the same name, enjoyed in the 18th century, was prepared by boiling barley in water, then mixing the barley water with white wine and other ingredients, such as borage, lemon and sugar. In the 19th century, a different barley wine was made prepared from recipes of ancient Greek origin.^[5]

Nonalcoholic drinks such as barley water^[5] and roasted barley tea^[64] have been made by boiling barley in water. In Italy, barley is also sometimes used as coffee substitute, caffè d'orzo (coffee of barley). This drink is obtained from ground, roasted barley and it is prepared as an espresso (it can be prepared using percolators, filter machines or cafetieres). It became widely used during the Fascist period and WWII, as Italy was affected by embargo and struggled to import coffee. It was also a cheaper option for poor families (often grown and roasted at home) in the period. Afterwards, it was promoted and sold as a coffee substitute for children. Nowadays, it is experiencing a revival and it can be considered some Italians' favourite alternative to coffee when, for health reasons, caffeine drinks are not recommended.

Half of the United States' barley production is used as livestock feed.^[65] Barley is an important feed grain in many areas of the world not typically suited for maize production, especially in northern climates—for example, northern and eastern Europe. Barley is the principal feed grain in Canada, Europe, and in the northern United States.^[66] A finishing diet of barley is one of the defining characteristics of western Canadian beef used in marketing campaigns.^[67]

As of 2014, an enzymatic process can be used to make a high-protein fish feed from barley, which is suitable for carnivorous fish such as trout and salmon.^[68]

Barley straw, in England, is placed in mesh bags and floated in fish ponds or water gardens to help prevent algal growth without harming pond plants and animals. Barley straw has not been approved by the EPA for use as a pesticide and its effectiveness as an algae regulator in ponds has produced mixed results, with either more efficacy against phytoplankton algae versus mat-forming algae, or no significant change, during university testing in the US and the UK.^[69]

Barley grains were used for measurement in England, there being three or four barleycorns to the inch and four or five poppy seeds to the barleycorn.^[70] The statute definition of an inch was three barleycorns, although by the 19th century, this had been superseded by standard inch measures.^[71] This unit still persists in the shoe sizes used in Britain and the USA.^[72]

As modern studies show, the actual length of a kernel of barley varies from as short as 4–7 mm (0.16–0.28 in) to as long as 12–15 mm (0.47–0.59 in) depending on the cultivar.^[73][74] Older sources claimed the average length of a grain of barley being 0.345 in (8.8 mm).^[75]

The barleycorn was known as arpa in Turkish, and the feudal system in Ottoman Empire employed the term arpalik, or "barley-money", to refer to a second allowance made to officials to offset the costs of fodder for their horses.^[76]

A new stabilized variegated variety of H. vulgare, billed as H. vulgare varigate, has been introduced for cultivation as an ornamental and pot plant for pet cats to nibble.^[77]

In English folklore, the figure of John Barleycorn in the folksong of the same name is a personification of barley, and of the alcoholic beverages made from it: beer and whisky. In the song, John Barleycorn is represented as suffering attacks, death, and indignities that correspond to the various stages of barley cultivation, such as reaping and malting.^[78]