missouri 2006). In US the area under cultivation of barley and wheat is continuously decreasing while that under corn and soyabean is increasing. Total area under barley cultivation has decreased from 9 million acres in 1991 to about 3. 5 million acres in 2006 and accordingly the total production of barley has also decreased from about 9 million ton in 1991 to just 4. 4 million ton in 2005. US production averages 400 million bushels per year with an annual value of $923 million as a raw commodity (1988 1997). In USA production of the malt barley is mainly in the western states.
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. Malting and Brewing It is imperative to examine the malting, brewing and fermentation process in primarily to understand the quality requirements for the barley to be use for production of beer.
Various unit processes in production of beer are making malt, drying and milling of malt, producing wort, brewing, fermentation, maturation and bottling. We will examine each of the unit processes in somewhat detail. In the malt house, barley grain germination is initiated by the uptake of water in a steeping vessel. The grain imbibes water during controlled cycles of water spraying or water immersion followed by aeration, until the water content of the grain reaches 42 to 48%. Water enters the grain via the embryo, and after approximately 24 hours, the first visible sign of germination is the appearance of the root, as a white chit.
The grains are then transferred to malting beds where germination is allowed to proceed over a period of around 5 days. The speed of germination is controlled by temperature and aeration of the malt bed, while moisture content is maintained by spraying. Further embryo growth, with the appearance of rootlets and acrospires, can lead to root entangling. The grain bed is regularly turned with a rotating screw to prevent grains matting together. Green malt, produced after five days of germination, is kiln dried and partly cooked in a forced flow of hot air.
Hydrolases produced during malting are partially inactivated during this process. Malt color, enhanced by kilning at higher temperatures, may be desirable for production of darker beer, but it leads to further heat-inactivation of hydrolases. The brittle malt rootlets are separated from the malt and utilized in animal feeds. The kilned malt is stable for storage and has a friable texture suitable for the milling process which proceeds brewing. The brew house consists of brewery buildings housing machinery and equipment for the production of wort.
Processes taking place here include milling of the kiln dried malt, mashing, filtration and wort boiling. The malt is milled into fine grits to ensure good access of water to grain particles in the subsequent phase of beer production. Milling energy is a good indication of malt quality, where homogeneously modified malt has a lower milling energy. Malt may be supplemented with solid adjunct, i. e. a sugar source such as flaked or roasted barley, in order to impart specific flavor or colour characteristics to the finished beer.
Milled malt is mixed thoroughly with two to four volumes of water to yield mash, and subjected to a process denoted mashing that fundamentally is an extension of malting with the action of various enzymes. Boiled, gelatinized starch from maize or rice grains may be supplemented as adjunct during mashing to achieve a higher content of fermentable sugars. At the end of the mashing operation, soluble substances and residual solid particles are separated by filtration into sweet wort and spent grains, respectively.
Factors influencing mash filtration are complex and range from physical effects, such as particle size, to high viscosity caused by gum and protein aggregates. In the next process in the brew house, hops are added to the wort as a source of bitter substances, which are solubilized during wort boiling (> 1 h) and give beer its characteristic taste and aroma. In addition, wort boiling serves to denature enzymes and other proteins, sterilizes the wort, and yields a darker liquid which is an excellent medium for subsequent fermentation with brewers yeast.
During the primary fermentation, the fermentable sugars, mainly maltose and glucose are converted to ethanol and carbon dioxide. This action is performed by the brewing yeast, which during the brewing process also produces many of the characteristic aroma compounds found in beer. At the end of the primary fermentation, the yeast cells flocculate and sediment at the bottom of the fermenter and can be cropped and used for a new fermentation. Not all yeast cells sediment; some will remain in suspension, and these cells are responsible for maturation of the beer.
During this process the off-flavor, diacetyl is degraded to below the taste threshold. The fermentation characteristics of brewers yeast are strain-dependent and are genetically inherited. Much of the genetics of Saccharomyces yeasts has been elucidated, and the knowledge gained, forms the basis for breeding of brewing yeast. Thus, new types of beer with altered aromas can be produced with yeast strains selected through breeding. After fermentation the temperature is lowered and the beer is maturated for a period during which the off-flavor component diacetyl is assimilated by yeast cells.
Mature beer is then chilled to a temperature of -2 oC for a couple of days. By doing so the colloidal stability of the beer is greatly improved due to precipitation of protein-tannin complexes, which are only sparingly soluble at low temperature. The beer is now ready for final stabilization, which removes further amounts of proteinaceous matter and/or tannins, and subsequent filtration. The bright beer so obtained, and adjusted to the correct carbon dioxide content, is now ready for bottling.
When the residual yeast cells have been removed it is of utmost importance that oxygen uptake is reduced as much as possible, since oxygen will damage the flavor stability of the beer and, despite intensive stabilisation, also impairs its colloidal stability. Finished beer is either bottled or canned or filled into kegs. It may be tunnel pasteurized, flash pasteurized or aseptically bottled. In either case the beer must appear fresh, bright and without faults to the customer and hence the quality is a matter of great concern. The beer must also be free from micro-organisms to ensure wholesomeness and biological stability.
The ethanol content must obey fiscal rules but is also of major importance for the flavor of the beer. This is further influenced by a wide range of compounds that may be present in even very small amounts. Visually the finished beer must form nice foam on pouring; it must have an attractive colour. Despite use of the choicest raw materials and careful brewing performance the beer is a fragile liquid, especially when not stored cold. The fine balanced aroma of fresh beer is eventually replaced by a less attractive smell and likewise the taste deteriorates. The basis for this decay is a matter of intense research.