Brewing

Brewing (and malting) is nowadays conducted in well-designed and highly hygienic facilities, for the most part fabricated from stainless steel. The equipment is repeatedly cleaned using regimes of acid or caustic, followed by thorough rinsing with clean water and perhaps a sterilant of the type that would nd use in the domestic kitchen.
In the brewery, the malted grain must rst be milled to generate relatively ne particles, which are then intimately mixed with hot water in a process called mashing. Mashes typically have a thickness of around three parts water to one part malt and contain a stand in the vicinity of 65°C. At this temperature the granules of starch are converted in a transition called gelatinisation into a 'melted' form that is much more susceptible to digestion by amylases. These enzymes are developed during malting, but only start to act once the gelatinisation of the starch has occurred in the mash tun. Some brewers will add starch from other sources, such as unmalted barley, maize or rice, to supplement that from malt. These other sources are called adjuncts. It may be neces­sary for the brewer to add extra enzymes at this stage, to help deal with some of these adjuncts. Many brewers, though, outlaw the adoption of such 'exogenous' enzymes, even though they are fully recognised as safe and are derived from harmless organisms, e.g. Aspergillus and Pencillium, which naturally thrive throughout nature, including on the surface of grain (Flannigan 2003).
After a period typically of one hour, the liquid portion of the mash, known as wort, is recovered in a 'lautering' or ltration operation and run to the kettle where it is boiled, again typically for an hour. Boiling serves various functions, including sterilisation of wort, precipitation as 'trub' of proteins and tannins (which would otherwise come out of solution in the rushed beer and cause cloudiness), and the driving away of unpleasant grainy characters that originate in the cereal. Many brewers add some adjunct sugars at this stage, and most brewers also introduce at least a proportion of their hops.
The hops have two principal components: resins and essential oils. The resins (so-called a-acids) are changed ('isomerised') during boiling to yield iso-a-acids, which provide the bitterness to beer. This process is rather inef cient. Nowadays, hops are often extracted with lique ed carbon dioxide and the extract is either added to the kettle or is isomerised outside the brewery for addition to the nished beer (thereby avoiding losses due to the tendency of bitter substances to stick on to yeast).
The oils in hops are responsible for the 'hoppy nose' on beer.
After the precipitate produced during boiling has been removed, the hopped wort is cooled and pitched with yeast. There are many strains of brewing yeast (Saccharomyces cerevisiae), and brewers carefully select and maintain their own strains because of their importance in determining brand identity. Yeast needs a little oxygen to trigger off its metabolism, but otherwise the alcoholic fermentation is anaerobic. Ale fermentations are usually complete within a few days at temperatures as high as 20°C, whereas lager fermentations at as low as 6°C can take several weeks. Fermentation is complete when the desired alcohol content has been reached and when an unpleasant butterscotch a-vour, which develops during all fermentations, has been mopped up by yeast. The yeast is harvested for use in the next fermentation. It may be washed with acid to eliminate contaminating microbes that can produce non-volatile nitrosamines (Simpson et al.
1988).
In traditional ale brewing the beer is now mixed with a small quantity of hops (to supplement hoppy avour), some priming sugars and isinglass nings, which settle out the solids in the cask. Isinglass is basically hydrolysed collagen, a protein found in many animal tissues. The collagen used for brewing comes from the swim bladders of certain species of sh that breed in the South China Seas. The swim bladders are dried, and then partially hydrolysed using sulphurous acid to generate a solution that has good capability for reacting with beer proteins to form large aggregates, which precipitate and settle. Under Draft Directive 2000/13/EC of the European Union it will in future be required that process aids or ingredients that are included in one of the major aller­gen groups be labelled. As sh and sh products are in the list that forms an annex to the Directive, this means that isinglass would need to be declared. Phillips (2003) has argued convincingly why this seems preposterous, for the collagen is vastly modi ed during processing and the levels that survive into beer are minimal.
In traditional lager brewing the 'green beer' is matured by several weeks of cold storage, prior to ltering. Filtration generally involves the use of lter aids that keep the lter bed loose and prevent it from clogging up. The two main types of lter aid are kieselguhr and perlite. They leave no residue in the beer.
Nowadays many beers, both ales and lagers, receive a relatively short conditioning period after fermentation and before ltration. This conditioning is ideally performed at -1°C for a minimum of three days, under which conditions more proteins drop out of solution, making the beer less likely to go cloudy in the package or glass. The long-term stability of beer may also be aided by the use of materials downstream that remove haze-forming protein or polyphenol. For the latter, the one choice is polyvinyl-polypyrrolidone. Protein may be removed in three ways: by adsorption on silica gels that are made from sand, by precipitation with tannic acid derived from gallnuts, or by hydrolysis with the enzyme papain from the pawpaw. This is the same enzyme that comprises meat tenderiser.
The ltered beer is adjusted to the required carbonation before packaging into cans, kegs or glass or plastic bottles. The packaging operations are rigorously designed to ensure that the product is delivered in secure (tamper-proof or at the very least tamper-evident) packages that minimise the opportunity for air ingress (oxygen promotes staling). Modern packaging lines incorporate highly ef cient systems to ensure that packages will not contain foreign bodies and furthermore that such items cannot be introduced during the packaging process itself.
Countries such as the UK have regulations which stipulate that packaging materials may not react with or alter the organoleptic properties of the food which they contact (Partington 2003). Aluminium or stainless steel cans, casks or kegs, therefore, are lined with epoxy lacquer coatings to prevent metal from leaching into the relatively low pH beer.