Water

As already stated, most beers comprise 90-95% water and so its composition is critical as a determinant of beer quality. Brewing demands much more water (5-20 times) than the amount which ends up in the beer (UNEP 1996). A lot is needed for cleaning and for raising the steam needed for heating vessels.
The water must contain no taints or hazardous components and a brewer may treat all water coming into the brewery by procedures such as charcoal ltration and ultra-ltration (Katayama et al. 1987). The water must also have the correct balance of ions (Taylor 1990). Traditionally ale brewing was established in towns such as Burton-on-Trent in England. The level of calcium in the water of the region is relatively high (about 350 mg/L), and it is claimed that this is good for ales, whereas low levels of calcium, such as the less than 10 mg/L in Pilsen, is best for bottom-fermented lagers. In many places in the world the salt composition of the water is adjusted to match that rst used by the monks in Burton in the year 1295, a process known as 'Burtonisation'. Often the brewer will simply add the appropriate blend of salts to achieve this speci cation. To match a Pilsen-type water it is usually necessary to remove existing dissolved ions by deionisation, perhaps by a ltration technique.
Carbohydrates
While most of the sugar found in wort is fermented to ethanol by yeast, some carbo­hydrates remain in the beer. Furthermore, extra sugars ('primings') may be added to sweeten the nal product.
The carbohydrates surviving into beer from wort are the non-fermentable dextrins and some polysaccharide material. The dextrins are remnants of starch degradation, whereas the polysaccharides derive from cell walls in barley.
Most of the starch in the endosperm of barley survives malting, because it is rela­tively resistant to enzymatic hydrolysis over anything other than prolonged contact times. However, if starch is gelatinised (which can be likened to melting) by heat treat­ment, then its constituent molecules, amylose and amylopectin, become much more accessible to enzymes. Thus the start of brewing involves gelatinisation, typically at 65°C, a stage known as 'conversion'. Other cereals, which may be used as adjuncts, have starches that need higher gelatinisation temperatures, e.g. rice and corn, in which starch gelatinises over the range 70-80°C. As stated above, amylase enzymes in the malt degrade the gelatinised starch to fermentable sugars; however, a proportion (usu­ally around 20-25%) remains in the form of unfermentable dextrins. A range of beers is available, which are termed 'super-attenuated' but generally marketed as 'light', in which all of the available starch is converted into ethanol. To effect this, an exogenous heat-stable glucoamylase or pullulanase of microbial origin is often added to the mash or to the fermenter (Bamforth 1985a). It is not obligatory to approach the problem in this way. By judicious use of the mashing regime, and also perhaps the addition of an extract of lightly kilned or unkilned malt to the fermenter, the enzymes native to malt are suf cient to deal with all the dextrins.
The world's rst approved, genetically modi ed (GM) brewing yeast was transformed to express a glucoamylase; however, as yet this strain has not been used in any com­mercial operation (Hammond & Bamforth 1994). Indeed, no GM material is knowingly or deliberately introduced into beer by any brewer. The only commodities that are based overtly on products of gene technology are some of the commercial enzymes. However, most brewers do not use these and, where they are used, they are added to the mash, and are denatured and precipitated in the kettle boil. Even so, it needs to be stressed that GM commercial enzymes are themselves rigorously screened before approval for commercial use.
Another major carbohydrate component in brewing systems is in the cell walls of barley, a P-glucan comprising P 1-4 links (as in cellulose) but disrupted by occasional P 1-3 links. This molecule is very similar to the P-glucan that is found in oats and which is well known as the 'soluble bre' championed as part of oat-based breakfast cereals (Lasztity 1998). While one of the main purposes of malting is to degrade the cell walls through the action of P-glucanase enzymes during germination, in practice some glucan always survives into malt (Bamforth & Barclay 1993). Unless it is properly degraded it renders the wort extremely viscous, with attendant problems in the operations of separat­ing the wort from the spent grains and with downstream beer ltration (Bamforth 1994). Thus some brewers mash-in at low temperatures (say 50°C) to allow the P-glucanase (which is sensitive to heat) to act. Additionally a heat-stable glucanase from bacteria (such as Bacillus subtilis) or fungi (such as Trichoderma reesei or Penicillium funicu-losum) may be employed (Bamforth 1985a). Barley has been transformed to express a heat-resistant P-glucanase, but it is not yet cleared for commercial use (Mannonen et al. 1993). All of these efforts to eliminate P-glucan are important if production problems are to be avoided, as well as quality problems, for the glucan can cause hazes and pre­cipitates in beer. The beers that will contain the most residual glucan are those that are produced with a high charge of barley adjunct, for instance some well-known stouts. The products of P-glucan breakdown in malting and mashing are not fermentable by yeast, so they survive into beer. Even those beers in which most of the glucan has been converted to low molecular-weight oligosaccharides may be of some value as sources of bre, as it is now understood that any P-linked sugar, no matter how small, may retain some bene cial properties when they reach the lower gut (Schneeman 1999).
P-Glucan is not the only polysaccharide found in the cell walls of barley, the other being arabinoxylan. For reasons that are not entirely understood, this seems to survive malting and brewing more readily than does P-glucan, such that beers tend to contain more arabinoxylan than glucan (Schwarz & Han 1995). It also ranks as soluble bre. In the cell wall the arabinoxylan is covalently linked to ferulic acid (Ahluwalia & Fry 1986). This phenolic acid is released during mashing (McMurrough et al. 1996) and survives into beer (unless the beer is made with yeasts, such as those used in the fermentation of wheat-based beers, which contain an enzyme that can decarboxylate the ferulic acid to 4-vinylguiacol, a substance that gives the classic clove-like character to such products). There is huge interest in ferulic acid as an antioxidant (Kroon & Williamson 1999).