Barley (Hordeum vulgare L.)

Origin, taxonomy, and genetic systems
Growth requirements, physiological and adaptive traits
Production statistics, economics and marketing
Quality factors for malting, brewing, and other end-uses
Major diseases and insect pests
Genetic resources and breeding
References

Origin, Taxonomy, and Genetic Systems

Barley was one of the first domesticated cereals, most likely originating in the Fertile Crescent area of the Near East. Many references to barley and beer are found in early Egyptian and Sumerian writings that are more than 5000 years old. Archaeological evidence of barley cultivation has been found dating back to 8000 BC in Iran. There is now considerable evidence that the initial cultivation of barley in China and India occurred at a later date.

Cultivated barley is one of 31 Hordeum species, belonging to the tribe Triticeae, family Poaceae. It is an annual diploid species with 2n=14 chromosomes. The genetic system is relatively simple, while the species is genetically diverse, making it an ideal study organism. Molecular evidence has revealed considerable homology between barley, wheat, and rye. Among the wild Hordeum, there are diploid, tetraploid, and hexaploid species. Many are perennial. The species are native in various parts of the world.

Barley has a single floret in each spikelet. There are three spikelets at each node, alternating on opposite sides of the barley head or spike. In two-rowed barley, the central floret is fertile and the two lateral florets are sterile, resulting in a single seed at each node, giving the head a flat appearance (see the picture on the far right). In six-rowed barley, all of the florets are fertile (see the head on the left side of the picture). The central seeds are round and fat, but the laterals tend to be slightly asymmetric. A single head of barley can produce up to 80 seeds.

Photo Courtesy of the University of Minnesota Extension Service

Currently the wild ancestor of barley (H. vulgare subsp. spontaneum) is thought to be a subspecies of cultivated barley, and cultivated barley is classified in the subspecies vulgare. Wild barley has a brittle rachis and occurs only in the two-row form. Cultivated barley has a nonbrittle rachis and may be two-rowed or six-rowed. H. vulgare subsp. spontaneum may be a transitional form between the true progenitor of barley and the cultivated species.

Barley generally has several stems or tillers. The Barley tillers are round and erect, with conspicuous nodes and internodes. Like many grasses, the stem is hollow. The ability of the barley plant to send up new tillers in response to favorable environmental conditions is a useful mechanism for adapting to changes during the growing season. Two-rowed varieties usually have a higher number of tillers per plant and larger, heavier seed than six-rowed varieties. Six-rowed varieties on the other hand, usually have more seeds per inflorescence. Thus the compensatory effects of yield components lead to similar levels of yield potential. The straw of barley is generally weaker than wheat.

Growth Requirements, Adaptive Traits, Management Practices

While claims are often made about the wide adaptability of various cereal crops, barley may well be the champion. It is grown in a range of extreme environments that vary from northern Scandinavia to the Himalayan mountains to monsoon paddies. It is particularly noted for its tolerance to cold, drought, alkali, and salinity. Its rapid growth enables it to compete well with weeds and other grasses. It is earlier in maturity than wheat and other cereal crops. It is not well adapted to acid and wet conditions.   Photo courtesy Patrick Hayes, OSU

Requirements for inputs, particularly nitrogen, are relatively low. Barley should be grown under moderate nitrogen fertility conditions because high fertility will reduce kernel plumpness and increase lodging. The grain protein target for malting barley is 11.5% to 13%, which must also be considered in determining appropriate N fertilizer levels.

As a C3 plant, barley favors cool production conditions (15-30 °C) and moderate precipitation (500 - 1000 mm annually). Cultivars that are photoperiod sensitive require long days to flower. Both winter and spring habit types exist. For winter barley, a vernalization period of two to ten weeks below 50 °F is necessary. In general, winter barley genotypes are not as cold hardy as winter wheat. Highest commercial yields tend to come from central and northern Europe, where yields of 10 t/ha can be obtained under intensive management.

No barley variety is adapted to all environments and, in fact, very different gene pools have evolved in the major barley production areas of the world. The gene pools may be defined by essential physiological parameters that determine adaptation to a production environment - such as vernalization and/or photoperiod response - or they may be defined by evolutionary bottlenecks and the accidents of history, such as regional preferences for two-rowed or six-rowed varieties.

Types of barley

• Feed and malt types
• Hulled and hulless varieties
  • hulled types - the lemma and palea remain attached to the seed at maturity
    Hulled barley is the predominant type in the US and many other parts of the world.
  • hulless types - the seed threshes free of the lemma and palea (hull)
    Hulless barley is produced for various food and beverage uses in East Asia (primarily, China, Japan, and Korea). Hulless barley is an important subsistence crop in the Andes and Himalayan regions and in Ethiopia. In Canada, hulless varieties are commonly grown as feed for swine.
• Awned types predominate
  • Rough and smooth awn types
  • Hooded (modified awns) are used for silage and green chop
  • Awnless types exist

• Awned barley (Courtesy Patrick Hayes, OSU)	'Sara' hooded barley (Courtesy Patrick Hayes, OSU)

• Aluerone color variations
• colorless
• white
• yellow
• blue
• Waxy starch type (100% amylopectin) used for specialty food and feed
• Dwarf types are common; Taller types are used in rain-fed production regions
  

Production Statistics, Economics and Markets

Barley ranks fourth among the cereals in terms of total world production. The average production from 2000-2002 was 136,270,100 metric tonnes. The map below shows the distribution of production by country over the same time period.

Barley Production in the United States

• US production averages 400 million bushels per year with an annual value of $923 million as a raw commodity (1988 - 1997).
  
• Of the barley consumed domestically, approximately
  • 55% of the barley crop is used for animal feed
  • 39% for malt production
  • 3.5% as seed
  • 1.7% in food products
    
• Total value of the annual barley crop is
  • $184 million for barley and milled products
  • $48 million for malt and malt extracts
  • $332 million for beer.
    
• US production represents 5-10% of the world production.
  
• Largest importers of US barley are Japan and Mexico.

Major barley production areas in the USA by county

Historically, the production of malt has continued to shift to the west over time. This trend was
accelerated by the epidemic Fusarium head blight (Fusarium graminearum) in the upper Midwest. Idaho and the Pacific Northwest are increasingly important areas for malt barley production.

Quality Factors for Malting, Brewing and other End-uses

Barley is primarily used for animal feed. It is fed to beef cattle, dairy cattle, swine and poultry. In most cases, the whole barley kernel is rolled, ground, or flaked, prior to being fed. Feed efficiency improves with removal of hulls, grinding, or breaking of bran layer (efficiency = weight gain / weight fed).

• Dry rolling: cheap, but dusty
• Steam rolling: same efficiency, but better palatability
• Fine grinding: hammer mill for impact grinding
• Pelleting: force material through die

The second most important use of barley is for malt. Malt is used in beer, liquor, malted milk and flavorings in a variety of foods.

Barley is also used for food. Pearling barley involves removal of the hull by using abrasive rollers with paddles moving through a perforated steel cylinder.

U.S. Barley Grades are based on:

• Row number (2 vs 6)
• Malt vs feed use
• Test weight (50# bu for 2-row)
• Discount schedule
• Plumps: retained on 6/64” screen
• Thins:
  • through 5/64” screen for 6-row
  • through 5.5/64" screen for 2-row

Generally higher test weight and greater % plumps indicate better feed value and better malt quality.

Barley for malting

Two-rowed barleys are favored for malting throughout most of the world, but in the USA and Mexico, six-rowed barleys are used extensively for this purpose. Thus, there are no absolute definitions of malting and brewing quality, due to differences in malting and brewing practices and consumer preferences.

The American Malting Barley Association (AMBA) provides specific quality guidelines for breeders in the US market: http://www.ambainc.org/ni/index.htm

Contract production for malting: specifications are given to growers for grain quality, plump kernels, and protein content.

The malting process

Source: http://www.howtobrew.com/section2/chapter12.html

The starch, protein and nucleic acid molecules that are stored in barley grains are not good nutrients for brewing yeast nor do they support the fermentation reactions performed by brewing yeasts. These large and structurally complex compounds must be partially or, in some instances, fully degraded into their component sugars, amino acids, and nucleotides before the yeast can use them. When barley seeds germinate, hydrolytic enzymes are synthesized or converted to active forms that can readily degrade these large compounds.

Malting is controlled sprouting - A complex interaction of genes involved in germination, growth and development.

Steps in malting:

1. Steep: raise moisture to 42-44% uniformly through kernel
• If too short – poor malt
• If too long – mold and bacteria grow
2. Germination : on beds with forced air and 100% RH 15 °C temp.
   Releases alpha-, beta- amylase, glucosidase, dextrinase.
   These enzymes are temperature stable during drying (kilning).
3. Kilning : reduces moisture and dries malt
4. Browning : adds flavor and color
5. Optional bleaching : reduces color

Changes in kernel composition and enzymes during malting

During malting, the acrospire (the plant shoot) grows along one side of the kernel. As it grows, pre-existing enzymes are released and new enzymes are created in the aleurone layer which "modify" the endosperm (the protein/carbohydrate matrix starch reserve) for the acrospire's use.

Malted barley is the source of the sugars (principally maltose) which are fermented into beer. The grain partially germinates, releasing enzymes in the aleurone layer (outermost layer of the endosperm). New enzymes are created that break down the endosperm's protein/carbohydrate matrix into smaller carbohydrates, amino acids and lipids, and open up the seed's starch reserves. The endosperm is composed of large and small starch granules that are packed in a protein matrix. The cell walls within the matrix holding the starch granules are primarily composed of beta-glucans (a type of cellulose), some pentosans (gummy polysaccharide) and some protein. The degree to which the enzymes unpack the starch granules (i.e. breakdown the endosperm) for use by the growing plant (or brewers) is referred to as the "modification." It refers to all of the polymer-degrading processes that occur during malting.

One visual indicator that a maltster uses to judge the degree of modification is the length of the acrospire which grows underneath the husk. The length of the acrospire in a fully modified malt will typically be 75-100% of the seed length. Drying is used to stop the malting process when the proper balance between resources converted by the acrospire and resources consumed by the acrospire has been achieved.

The purpose of malting is to create these enzymes, break down the matrix surrounding the starch granules, prepare the starches for conversion, and then stop this action until the brewer is ready to utilize the grain. After modification, the green malt is gently dried with heat (kilning) and the acrospire and rootlets are knocked off by tumbling. The kiln drying of the new malt denatures many of the enzymes, but several types remain, including the ones necessary for starch conversion. The amount of enzymatic starch conversion potential that a malt has is referred to as its "diastatic power".

Beta glucans are the soluble dietary fiber component of barley and oat bran. B-glucan is thought to have serum cholesterol reducing properties and occurs in highest amounts in the endosperm of barley and oats. B-glucan also is important for the malting industry and indicates how well the endosperm is modified. High levels of b-glucan cause a viscous wort that may cause problems with filtration or hazy beer. Thus, lower levels of b-glucan are preferred for brewing.

Brewing

Steps in Brewing

1. Malted barley is soaked in hot water to release the malt sugars.
2. The malt sugar solution is boiled with hops for seasoning.
3. The solution is cooled and yeast is added to begin fermentation.
4. The yeast ferments the sugars, releasing CO₂ and ethyl alcohol.
5. When the main fermentation is complete, the beer is bottled with a little bit of added sugar to
provide the carbonation.

Mashing - the hot water soaking process that provides the right conditions for the enzymes to convert the grain starches into fermentable sugars. The basic light colored malts such as pale ale malt and pilsener malt need to be mashed to convert the starches into fermentable sugars.

Adjuncts - fermentables not derived from malted barley.

Extract efficiency - typical amount of fermentable and non-fermentable sugars obtained from the grain.

German or US specialty beers use straight barley malt. Most brewers use adjuncts of rice, corn, wheat, or other grits to provide an additional carbohydrate source. Hops are added for ‘bitters’. Yeast is Saccharamyces carlsbergensis, occasionally S. cerevisiae.

The malt is treated with water under appropriate conditions (“mashing”) to obtain an extract (wort) that must perform several critical functions.

1. The extract must provide adequate nourishment to the yeast so that fermentation can occur.
2. The extract must provide sufficient fermentable sugars to enable the yeast to produce the desired levels of alcohol.

A high quality malt will contain the right amount of hydrolytic enzymes and metabolites to fulfill these requirements and will have the right degree of friability to allow many of its components to be readily solubilized during mashing. During malting and mashing, the barley starch should be almost completely degraded into sugars that can be utilized by the brewing yeasts, whereas only about 45% of the barley protein should be solubilized. Too much protein solubilization is thought to result in beers with poor foaming characteristics. When insufficient protein hydrolysis occurs, the remaining proteins may interact with polyphenols to form beer haze precipitates.

Four amylolytic enzymes are generally thought to participate in converting the starch in malted barley into fermentable sugars: these are a-amylase, b-amylase, a-glucosidase and limit dextrinase. During brewing, amylase enzymes digest amylose (linear starch) and amylopectin (branched starches) into hexose sugars. The sugars are a nutrient source for the yeast to facilitate fermentation. Sufficient sugars are needed to obtain the desired alcohol level.

Barley Diseases and Pests

Many of the important diseases and insect pests on barley also attack wheat.

There are fewer problems with disease and insect pests in the western US, where production conditions are drier with low relative humidity.

Major diseases

Source: http://plant-disease.ippc.orst.edu/plant_index.cfm

Barley yellow dwarf virus (BYDV)

BYDV is spread by several species of aphid. Symptoms can be variable and may be confused with nutrient deficiencies or stress. The severity of the damage will also be variable, depending on the susceptibility of the variety, virulence of the strain, the time of infection, and environmental conditions. The disease is most severe when the weather is cool and moist. The virus can be avoided to some extent by planting very early in the spring or late in the fall. Use of resistant varieties or systemic insecticides also provide control.

Fusarium head blight or scab (FHB)

http://www.cdl.umn.edu/scab/scab.html

FHB is a fungus that attacks both wheat and barley. Within the last dozen years there have been outbreaks of FHB in the Midwestern and Eastern states of the USA, as well as in Central and Eastern Canada. FHB is increasingly threatening wheat and barley food supplies worldwide.

There are several Fusarium species that can cause FHB, but the one that has been problematic in the Midwest in recent years is F. graminearum. Spread of the disease is favored by extended wet periods.

The damage due to the pathogen is two-fold. Infested cereals show significant reduction in seed quality and yield due to discolored, shriveled "tombstone" kernels, and secondly, scabby grain is often contaminated with mycotoxins making it unsuitable for food, beer production, or feed.
The U.S. Wheat and Barley Scab Initiative (USWBSI) is a major initiative that aims to develop effective control measures as quickly as possible.

Barley stripe rust (BSR)

Source: http://www.ars.usda.gov/is/AR/archive/aug99/barley0899.htm

Barley stripe rust is caused by a fungus Puccinia striiformis f. sp. hordei that was accidently introduced from Europe into South America in 1975. It first appeared in the US in 1991. It is particularly devastating in the cool, moist environments in the Pacific Northwest. BSR spreads by powdery, yellow spores. The spores are produced in large, yellow stripes between leaf veins, giving the leaves a striped, rusty appearance. When infection is severe, losses of 50% are common. Resistant cultivars are available, and efforts are underway to develop adapted, malting varieties with resistance for the PNW.

Photo courtesy of Patrick Hayes, OSU

Insects

Important insect pests of barley include:

• Green bug (Toxoptera graminum)
• Russian wheat aphid (Diuraphis noxia)
• jointworm (Tetramesa hordei)
• cereal leaf beetle (Oulema melanopus)
• Barley thrips (Limothrips denticornis)
• aphids

Genetic Resources and Breeding

There is extensive natural variation in barley, which makes it quite responsive to artificial selection.

Major germplasm collections

• USDA National Small Grains Collection
• Canada's Plant Gene Resources
• Nordic Barley Gene Bank (Sweden)
• ICARDA (Syria)
• Major collections in Germany, Japan, and the former Soviet Union

In the USA, there is both public sector and private sector involvement in barley improvement research.

Hulless (naked) barley - controlled by a single recessive gene that can be easily incorporated into adapted germplasm. Not suitable for malting.

Waxy types - controlled by a single gene that imparts 100% amylopectin starch.

Breeding and selection for malt quality

• Evaluations are expensive, limiting number of assays possible
• USDA-ARS lab in Madison, WI
• Micro-malting tests, enzyme assays
• Pilot-plant brewing
• Malt-house trials
• Final: taste tests
• Variety development: often 15 yr process
• Final release of malting variety is highly dependent on ‘product quality’ assessments. A poor sample, poor malt, or poor taste test can kill potential variety.

Breeding strategies

Most common: pureline variety development through conventional breeding techniques.

OSU breeding strategies: application of doubled haploid techniques and tissue culture for rapid development of homozygous purelines.

Funding for barley improvement

American Malting Barley Association (AMBA) has been highly successful in securing support through industry support and activities of a full-time director.

Examples: scab initiative, genomics funding, support for NSGC at Aberdeen, funding for ARS quality labs.

References

American Malting Barley Association (AMBA). http://www.ambainc.org/

BarleyWorld. 2004. Web site of the Barley project at Oregon State University.
http://barleyworld.org

Hayes, P.M., A. Castro, L. Marquez-Cedillo, A. Corey, C. Henson, B.L. Jones, J. Kling, D. Mather, I. Matus, C. Rossi, and K. Sato. 2003. Genetic diversity for quantitatively inherited agronomic and malting quality traits. In R. von Bothmer, H. Knüpffer, T. van Hintum, and K. Sato (eds.), Diversity in Barley (Hordeum vulgare L.). Elsevier Science Publishers, Amsterdam. pdf file

National Barley Foods Council. 2003. BarleyFoods website. http://www.barleyfoods.org/

Nilan, R.A., and S.E. Ullrich. 1993. Barley: Taxonomy, origin, distribution, production, genetics, and breeding. In W. MacGregor and R.S. Bhatty (eds.) Barley chemistry and technology. American Association of Cereal Chemists, Inc., St. Paul, MN.

North American Barley Genome Mapping Project. 2003.
http://barleyworld.org/NABGP.html

Oregon State University Extension Service. On-line guide to disease control. http://plant-disease.ippc.orst.edu/plant_index.cfm

Palmer, J. 1999. How to Brew. http://www.howtobrew.com/

Washington Barley Commission. 2003. http://www.washingtonbarley.org/mainset.html