Barley is the primary cereal used as the source of carbohydrates for brewing beer. It is designated Hordeum vulgare, a species of monocotyledonous grass, of the family Gramineae, which originated in the Fertile Crescent of the Middle East (formerly Mesopotamia and its surroundings, now Syria, Iraq, and neighboring lands).
The cereal spread north into and across Europe, becoming domesticated and improved for local agronomic conditions and weather as it went. It is a versatile crop, and is now grown in regions from the equator to the subarctic, from sea level to great altitudes, in areas of substantial rainfall and in deserts.
Modern breeding techniques have produced excellent varieties that deliver benefits to growers in all parts of the world, but the selection of a small number of strains in the middle of the 20th century to be the parents for modern elite lines has resulted in a relatively narrow gene pool for current maltsters and brewers. There are now many landraces of barley in different regions of Europe, fortunately held in academic collections, which retain different characteristics from the original genetic properties of ancient barleys. These landraces are not purebred varieties, but are instead a mixture of strains that results in a consequent breadth of the gene pool. It is certain that these older types of barley will provide wonderful resources for breeding improvements, and that they are needed in barley, as in other major crops, to meet the challenge of feeding the world during the 21st century.
Varieties were first selected from the best of the plants observed in the field by growers, an early example being Chevalier, which was selected in 1824 in England.
Individual grains of barley vary tremendously in size. Units of measurement include thousand corn weight (TCW) which may vary from 5 to 80 g, although malting varieties fall into the middle of this range at 30 to 45 g. Thickness varies from 1.8 to 4.5 mm; as this is a critical measurement for brewers to be able to set their malt mill correctly, it is best to have a narrow range of thickness. Although the length of a barleycorn may vary from 6 to 12 mm, for several centuries the barleycorn was the base standard of length for England and Wales. The inch (25.4mm) was defined as three barleycorns, so an average corn was deemed to be 8.5 mm in length—but there was plenty of room for argument over such a natural standard!
Barley, although supplanted by wheat as a cereal of choice for bread-making in most of the world, still ranks as the fourth cereal by tonnage grown annually. It is important for animal feed, barley breads, and in other cookery as flour, flakes, or whole corn (often dehulled or pearled), and for malting to produce the primary ingredient for beer-brewing and whiskey production. Although other cereal grains may be made into malt, barley really is the pre-eminent cereal for this process. Its husk offers protection against the damage caused by handling the grain, particularly the regular turning to separate the grains during germination. The high moisture content of the grains at this stage renders all cereals more fragile. The husk then acts as the filtration medium in the brewhouse, allowing the brewer to achieve bright worts and have better control of fermentation conditions and subsequent flavors.
Cultivated barley is classified in various ways. Common distinctions are between winter and spring sown grain, and between two-row and six-row. In shorthand, these lead to general classifications of, for example, 2RW (two-row winter), or 6RS (six-row spring). There is a further distinction made between feed and malting varieties.
Barley has six spikelets arranged in triplets that alternate along the main spike that forms the spine of the ear of barley (the rachis). In wild barley only the central spikelet of each three is fertile, while the other two are sterile. This condition is retained in those cultivars known as two-row barleys, which then appear to have two rows of corn, one along each side of the ear from top to bottom. A single mutation in the barley gene can result in fertile lateral spikelets, producing six-row barleys, with six rows of corns along the length of the ear. Six-row barleys have four of the corns from any set of six slightly thinner than the other two; the smaller corns are also twisted as they grow from their position on the rachis. This diversity of corn size makes six-row barley less attractive to brewers for two main reasons: the small corns have a lower starch content and higher protein content (and hence lower alcohol potential), and the mills in the brewhouse are most easily set to produce an optimum grist when the malt corns are even in size. However, it is the totality of the economics in the supply chain from the farm to the beer glass that influences exactly which type of barley is grown for the maltster and brewer to use—so the agronomic yield to the farmer may be greater from a six-row variety, and this can outweigh the loss of carbohydrate in the small corns. In Europe, the result is mostly two-row varieties with an occasional six-row variety emerging from the breeding program for a few years, which can compete successfully before becoming outclassed. However, six-row varieties are extensively and successfully grown and used in the United States and elsewhere in the world for malting and brewing.
Certain varieties need to be sown in the autumn; these are known as “winter” varieties because they are in the ground over winter. However, severe continental winters will kill most barley varieties—barley is not hardy enough to survive extreme cold—so countries in a continental land mass will generally grow and malt spring varieties. Winter varieties have agronomic advantages—in particular, they lead to higher yields and earlier harvesting. This latter benefit brings with it earlier sale of the crop and payment for it, extended use of combining equipment, early availability of land for tillage for the following crop, and good utilization of equipment and manpower, plus the opportunity to sow the following crop—perhaps high-yielding winter wheats—at the optimum time. Having arable land covered over winter helps to prevent run-off of nitrogen into watercourses. On the downside, winter crops are exposed for longer to diseases and will need additional fungicide sprays (unless they are bred to be resistant). Spring barley gives the opportunity for excellent weed control. For example, the pernicious weed blackgrass is related to barley and cannot be selectively killed, so allowing it to germinate on fallow soil over winter gives the opportunity to use a general weed killer in the spring before sowing barley as the commercial crop. Spring varieties yield best when sown as early as possible, allowing for the end of severely cold weather and then dependent on the land being dry enough for the farmer to be able to take his machinery across it.
The best malting varieties will take up water rapidly during steeping, commence germination rapidly and evenly, and deliver high enzyme activity and high extract potential in a friable grain of malt.
When a farmer is choosing whether to grow barley for the feed market or the malting market, he will expect to be able to charge a premium for the latter sector. This is because malting varieties tend to yield less than feed and less nitrogen can be applied during the growing season in order to meet maltsters’ specification—reducing yield further still—so there is a direct effect of fewer tons/hectares that needs to be recognized by a higher price per ton. There is also a risk factor with growing malting barley: that of possible failure to meet specification. With feed barley, the specification is not onerous. Potential malting barley that lacks germinative capacity, has pre-germinated, or is not acceptable for other quality reasons will be downgraded to the feed market. The grower, consequently, needs a risk premium to account for the occasions when this happens to his crop.
The key physical feature for the maltster is the distinction between the embryo and the endosperm. The embryo is the baby potential plant. The endosperm, which accounts for around 75% of the weight of the grain, is the food reserve that will see the growing embryo through its first few days until it can produce leaves. These will harness the sun’s energy to fuel continued growth to maturity as a new barley plant.
The main component of the food source is carbohydrate, stored as starch in granules, but there are also storage and functional proteins, which will be needed for the growing corn to develop material for new cells to grow.
The other primary features are the husk (comprised of palea and lemma wrapped around opposite sides of the corn); the pericarp, also surrounding and protecting the whole corn; the testa, which is a barrier to inward diffusion of salts and outward diffusion of sugars, amino acids, and other solubles from inside the grain; and the aleurone layer, which receives a signal from the embryo to start growing and which releases enzymes into the endosperm to start to mobilize the food reserves to feed the embryonic plant.
The embryo has several important features: the scutellum, which releases the messenger molecule gibberellic acid to stimulate the aleurone layer; the coleorhiza and coleoptile, which will develop into root and shoot, respectively; and the micropyle, a small hole in the proximal (embryo) end of the grain. Water enters readily through the micropyle during steeping, and it is also the exit route for the chit and subsequent growing rootlets that develop in the first days of malting. Hydration of the embryo is the signal for the baby plant to start growing.
The malting process aims to harness the natural growth tendency of the barley grain, allow it to proceed to a certain point, and stop it there, producing a package of natural compounds that can be further processed by the brewer to produce a nutritious wort for fermentation by yeast. The key concept is that of the nutrient package: the barley plant needs energy from carbohydrate and the building blocks for proteins, plus the vitamins necessary for its biochemical processes, to proceed, and so does the yeast. It is the maltster’s and brewer’s role to adapt the life process and materials of the barley to feed the yeast.
Accordingly, as the embryo is hydrated and sends out the gibberellins to call for nutrition from the endosperm, the maltster is looking for enzyme development to start to break down the cell walls of the starch granules in the endosperm and to deliver raised levels of amylase activity into the grain, but not to allow these amylases to break down too much starch before delivery of the malted grain to the brewery.
The physical characteristics of the two sources of starch are different with respect to their gelatinization temperature. Gelatinization is a phase change (similar to that in water when changing from ice into liquid) in which starch moves from a semi-crystalline phase to an amorphous phase. The large starch granules gelatinise at 140°F–149°F (60°C–65°C) and are readily hydrolyzed in their amorphous phase by amylases during mashing in the brewhouse. Starch in the small granules has gelatinization temperatures in the range 167°F–176°F (75°C–80°C), and so is not broken down by mash amylolytic activity and will form a paste that will slow run-off from the mash and cause haze in the beer that may be problematic at the later filtration stage.
Sound storage after harvest of any cereal crop is essential to protect the quality and against commercial losses. Threats to malting barley include mold, insects, mites, rodents, and birds. The vertebrates can be excluded from grain stores physically, and minor infestations can be cleared up quickly by suitable bait. Protection from the remaining hazards is best achieved through control of moisture and temperature. In warmer, drier climates, grain will come off the combine harvester at a suitable moisture content (around 12%), in more temperate climates it will be 14%–15%, and in wet climates it may rise to over 20% in rainy harvest seasons. The usual level of moisture regarded as safe for storage is 12%, although some maltsters are experimenting with 14%. At or below 12%, insects and mites will not proliferate. At 14%, the temperature becomes important, and ideally should be less than 50°F (10°C) within a few weeks of drying. In warmer countries, such a temperature is not possible without refrigeration, which is usually too expensive, so some losses to insect infestation may be expected. There are chemical insecticide protections, but fewer with tightening legislation, and again, these can be expensive. As a curative, fumigation with phosphine is feasible in closed silos, but much more difficult in flat stores. In either case, expert supervision is required.
Failure to protect against these threats to the corn can lead to loss of dry matter through the grain being eaten by the infesting species, to food safety issues with direct contamination, and to more serious food safety concerns with storage mycotoxins from mould growth. Local moist conditions in grain can undo otherwise good work looking after the bulk—the warmth of mold growth and insect infestation in a moist area can lead to condensation elsewhere in the bulk, with further infection and infestation possible as a result.
Sound storage will give the shelf life of over 12 months that is needed for one season’s barley to be processed in the maltings until the following crop becomes available.
In the natural cycle, cereal seeds have a disadvantage if they germinate immediately upon becoming ripe, as they will be attempting to grow into plants at the wrong time of year, with adverse weather conditions likely. Perhaps the clearest example is with spring varieties, which should not germinate until sown in the spring. The natural protection against early germination is dormancy, and this can be bred into or out of varieties. Too much dormancy gives maltsters problems with starting to malt the new season’s barley at a reasonable time after harvest, say, 6 to 10 weeks. Too little dormancy and the barley may start to shoot while still on the ear of a plant in the field during a wet harvest period. In a bulk of grain that is likely to exhibit unacceptable dormancy, storage may take place at 104°F (40°C) for a period of weeks to break this dormancy. This temperature should not be extended into several months, as there would then be an increased risk of insect infestation.
A maltster will want to put together a bulk of barley that is consistent throughout and meets certain quality standards. When barley is presented for delivery against a contract, the intake laboratory will check for variety, germinative capacity (GC), nitrogen content, moisture, and corn size profile, and will ensure that it is free from other cereal and weed seeds and free from mold and insects. Several of these parameters are commercial. For instance, failure to meet exactly the moisture specification may lead to an adjustment in the price to be paid for the consignment. The ability to germinate, however, is key to being able to process the grain, and it is an absolute hurdle for quality for acceptance to a maltings or intermediate store. The threshold is set by reference to the standard achievable by the supply chain from the farm through storage and is commonly a minimum of 98%. Any corns that do not germinate will pass through to the brewing process with unmodified gums, proteins, and carbohydrates that will lead to problems in the brewery. Small amounts can be accommodated by the surplus natural enzymes from the malt, but larger amounts will cause additional processing time and cost.
GC testing at intake can prevent dead corns from being delivered to the maltings. The test also shows those corns that may have started to germinate in the ear, termed “pre-germination,” and may continue germination on subsequent steeping, or may not, which can cause subsequent process problems and cost.
Once in store, to determine readiness for transferring barley into process, a test for germinative energy (GE) is carried out, which involves incubating 100 corns on a filter paper in a Petri dish, moistened with 4 ml of water, for 3 or, less commonly, 4 days, removing chitted grains each day. (Barley kernels that have been properly steeped and now show evidence of root growth are referred to as “chatted.”) GE scores of at least 98% are desirable, showing that grain has been stored with no loss of viability and that dormancy has been broken. An indication of the vigor of the grain sample is given by the daily count of chitted corns: the earlier that corns chit, in general, the better. In a parallel test, by wetting the filter paper with 8 ml of water, a measure of the water sensitivity (WS) of the grain can be made. The additional water maintains a film of water over the surface of the grains (limiting the amount of oxygen available to the embryo to start germinating) and gives an indication to the maltster of the appropriate steeping regime—lengths of wet periods and dry periods—for that barley.
Brewers have long been interested in whether the variety of barley can influence the flavor of the resulting malt and the flavor of the beer made from the malt. In the early 20th century Hugh Lancaster, in his book Practical Floor Malting, praised the “finest qualities of sound clear-grown Chevaliers” for the delicate flavor they could bring to pale ales. Most brewers have been content to brew with malts that presented no processing difficulties, and to achieve malt flavor variations in their beers by different malt specifications. The variety Pipkin, popular in the UK in the late 1980s and 1990s, was known to produce a high level of the precursor for formation of dimethyl sulphide (DMS) during the brewing process.
Most recently, in the first years of this century, there has been investigation into the flavor of Maris Otter and its effect on beer.
Craft brewers, in their search for deeper malt flavors in their beers, are showing a particular interest in “heirloom” barley varieties. As the topic of barley varietal flavor comes to the forefront, there is hope that barley breeders may yet develop efficient but flavorful crosses from older varieties.
The carbon footprint of barley is similar to other cereals, the principal components being the manufacture of nitrogen fertilizers and the emission of nitrous oxide from the soil during the growing season. These two factors alone account for 80% of the greenhouse gas emissions of intensively farmed barley. The remaining emissions are associated with the use of diesel fuel to power tractors and combine harvesters, those associated with manufacture of other inputs, any post-harvest drying, and those coming from storage and haulage of the crop. The most promising area for reductions would seem to lie in a switch to organic materials—compost, anaerobic digestate, and sewage sludge—to replace the industrially produced fertilizer, and in establishing a better understanding and subsequent control of the mechanisms of production of nitrous oxide in the soil.
Being a relatively low-nitrogen crop, the input of fertilizers is a little lower than for other cereals on an acreage basis, but not by weight of cereals produced. Similarly, nitrate run-off again is slightly lower for malting barley than from other cereals as a result of less nitrogen input per area.
The crop is fairly drought tolerant, which will prove an advantage, as water is now forecast to be in deficit in many parts of the world in the coming decades.
There can be no question that barley is a crop with a strong past and a bright future.