A common acid produced by a variety of yeasts and bacteria. A major spoilage flavour resulting from the growth of acetic acid bacteria in beer and detectable by a vinegar like aroma and taste. Production by acetic acid bacteria involves the oxidation of ethanol to acetic acid.
A procedure used to clean yeast of unwanted bacteria by incubating in a solution of acid at pH 2.2 immediately before fermentation. Contaminating bacteria are more sensitive to the acid than yeast and die.
Additional extract material added to the mash or copper. Generally non barley grain adjuncts such as maize, rice or wheat are added to the mash to allow barley enzymes to digest their starch while syrup adjuncts are added to the copper as they do not require digestion.
A carcinogenic toxin produced by the growth of certain moulds on grains. Aspergillus is a common type of mould which may do this. Low levels may be carcinogenic and barley and malt should be kept dry to prevent such growth.
Alcohol by volume (ABV)
A measure of the strength of a beer by the level of alcohol it contains. If measured by volume the units would be millilitres of alcohol per 100 grams of beer. Beer ABV ranges from 3% in weak ales and milds to 10% in strong ales and barley wines.
Alcohol by weight (ABW)
A measure of the strength of a beer by the weight of alcohol it contains. If measured by weight the units would be grams of alcohol per 100 grams of beer. Alcohol by weight is 0.85 alcohol by volume. Beer ABW ranges from 2.5% for weak ales and milds to 8.5% for strong ales and barley wines.
A non specific term for top fermenting beers as opposed to bottom fermenting lager beers. Historically ale was used to indicate a beer without hops or a strong beer.
An outer layer of cells in the barley grain surrounding the endosperm. These cells synthesise a amylase during malting in response to stimulation by gibberellic acid produced by the embryo.
One of the two major forms of starch found in the endosperm of barley and other cereal grains. Composed of linear chains of glucose molecules and digested by a and b amylase enzymes during mashing.
One of the two major starch digesting enzymes active during mashing. Only small amounts of a amylase are present in raw barley but much is synthesised during malting. In mashing a amylase digests internal bonds of amylose and amylopectin to release a range of sizes of simple sugars and larger dextrins.
One of the two major starch digesting enzymes active during mashing. Large amounts of b amylase are present in the raw barley grain before malting. In mashing b amylase digests amylose and amylopectin molecules by releasing maltose units from the non reducing ends of the starch chains.
One of the two major forms of starch found in the endosperm of barley and other cereal grains. Composed of a branched chain of glucose molecules and digested by a and b amylase enzymes during mashing.
Phenolic compounds released from malt during mashing. They may contribute to colour of wort and beer as well as complexing with proteins and precipitating to cause haze if not removed earlier in the boil and fermentation.
ATNC (Apparent Total N-nitroso Compounds)
A measure of the level of nitrosamine compounds in beer. These compounds arise from the nitrosating of amide or amine groups during malt production or by bacteria during fermentation. Levels in malt are today very low at less than 0.5mg per Kg due to careful management during kilning of malt. Levels due to bacterial action depend on the cleanliness of yeast used in fermentation. Acid washing of yeast will reduce these bacteria.
Microscopic organisms with limited cell structure and small size – generally less than 1m in length. Bacteria generally like neutral acidity but some species, particularly acetic and lactic acid bacteria are able to grow in beer and produce spoilage flavours.
The principle cereal grain used in brewing. Two species, Hordeum vulgare and Hordeum distichon are most commonly grown and many varieties exist some of which are planted in the spring others in the winter. The grains of barley are quite large and contain high levels of starch and also of digestive enzymes. Two row barleys are larger than six or four row barleys due to the selection of two rows of grains down the stem rather than the wild type six rows.
A classic strong ale with an ABV between 6.5 and 11, a bitterness between 20 and 50 and a wide range of colour. Flavours are generally pungent alcohol, ester and hoppy and taste moderately bitter with a thick and smooth mouthfeel.
An alcoholic beverage produced by the fermentation of sugars from malt and other cereals. Generally containing between 3 and 10% alcohol by volume (ABV) and with the flavours of malt and hops. Most beers are distinguished by their balance of bitterness and sweetness compared to wine which has a balance of sourness and sweetness. Many beers also have secondary flavours produced by yeast fermentation, for example esters producing fruity flavours.
A hydraulic pump used to pull beer from a cellar to the bar for dispense. Designed like a simple water pump it contains one way valves in a chamber to prevent backflow of the beer. Beer, pulled into the chamber through a rubber flap on the piston, is dispensed out through a spout which may be extended to reach the bottom of the glass and minimise turbulence. The long pulling handle is the characteristic emblem of cask ales which are typically dispensed using beer engines.
A deposit of mineral and organic materials in the fermenter due to the precipitation of calcium salts and proteins. May be difficult to remove and can shield contaminating bacteria so posing a hygiene hazard.
A vitamin essential for the growth of most brewing yeast. Adequate quantities are normally released from the malt by mashing.
One of the predominant beers served in Britain and renowned for its balance of bitterness, malt and fruitiness. Generally brewed from pale and crystal malts with high hop additions the beer is light in colour, often amber or gold, and rich in hop aroma. ABV is between 3.2 and 6.0, bitterness up to 50 IBU and colour up to 100 EBC but generally around 30. Ordinary, best and strong bitters may be recognised as sub styles and differ in strength of alcohol as well as level of hop and fruit character.
A major beer flavour produced by the effect of heat on the a acids from hops. These humulone compounds are isomerised by boiling and converted to iso a acids which taste bitter. Bitterness levels are measured in IBU (International Bitterness Units) where 1 bitterness unit = 1 mg of iso a acid per litre. Beers generally have bitterness levels between 20 and 50 IBU.
Beer fermented with a yeast which readily settles to the bottom of the fermenter. Typically using a lager yeast which also ferments at low temperatures – 8 – 12oC. Bottom fermentation allows the yeast to be cropped after the beer has been racked. However, the yeast is surrounded by trub precipitated in the cold break and will be less pure than top cropped yeast.
A genus of wild (non standard brewing) yeast which produce acetic various distinctive flavours including butyric acid, caproic acid and capric esters. Acetic acid can be produced in the presence of oxygen.Brettanomyces yeasts are common in the production of sour Belgian beers and may have been typical in traditional UK beers before brewers began to purify and manage their yeast strains.
Brewery conditioned beer
Beer which is fully matured in the brewery and dispensed into kegs or casks without its yeast. Such beer is typically filtered or pasteurised to provide stability and has a shelf life of 6 – 10 weeks compared to the 3 – 6 weeks for cask conditioned beer.
Beer racked off its sediment of yeast into a fresh container for dispense. Such beer does not require settling and may be served immediately. However, it has a very short shelf life of less than 24 hours and will stale easily due to the absence of yeast to absorb oxygen.
A distinctive type of British beer characterised by a moderate bitterness and strong malt character. Taste is malty and sweet with a full body and light hop and fruit. ABV is between 4.5 and 5.0% and colour up to 70EBC.
A historic fermentation system developed in Burton upon Trent whereby the fermentation is conducted in large casks and the yeast is propelled from the casks into a collecting trough through a long spout rising from the shive. The system is suitable for the highly flocculent yeast used in Burton beers and is said to produce specific and desirable flavour features. However, it is very labour intensive and expensive to operate due to the extensive and difficult cleaning required.
The surface of a heating element in contact with wort. May be internal to the copper or external so as to heat wort which is pumped over it in a recirculation loop.
Insoluble salt precipitated from wort by boiling and over time during the fermentation. Will form crystals which may become embedded in beer stone or remain suspended in the beer to cause a light haze. Inadequate or excessive calcium in wort may cause precipitation.
A material produced by the heating of sugars with or without the presence of nitrogen materials. Typically produced during wort boiling synthetic caramels may be added to beer to adjust or intensify colour and flavour.
Seaweed extract of carbohydrate polymers used as finings to accelerate settlement of protein trub at the end of boiling and yeast after fermentation.
Vessels for dispensing beer. Traditionally made from wood but today from stainless steel or, less frequently, aluminium. Typical shape is cylindrical with a belly to keep settled yeast away from the tap. When stillaged the top has a shive bung which is opened to allow air or gas into the cask. Beer is drawn from a tap inserted into the keystone bung in the side.
A simple two way or demand valve used to supply carbon dioxide gas to the head space of cask conditioned beer during dispense. This reduces the oxidation of beer by excluding air and so lengthens the life of the beer whilst retaining the carbonation and flavour.
Cask conditioned beer
Beer dispensed from a container containing live yeast which has been allowed to condition the beer by the production of carbon dioxide gas and maturation flavours.
A heating vessel used to incubate malt and/or adjunct grains before or during mashing. Many adjuncts have low levels of enzymes and require the addition of barley malt or of processed enzymes to digest their starch. This is performed in the cereal cooker while separation is conducted in a separate lauter tun.
A major species of a acid extracted from hops. It is isomerised to iso a acid and is said to have a harsh bitter character although this feature may arise from tannins associated with the acid.
The precipitated trub produced by boiling. Will settle as flakes when the wort is chilled and at the start of fermentation. It is composed of lipids, proteins and tannins and a good cold break is important to minimise haze formation in the final beer.
The protein species present in isinglass finings.
A boiling vessel for wort. Boiling kills residual microorganisms extracted from malt during mashing, stabilizes flavours and converts a acids into iso a acids so making wort bitter. It is an essential stabilization stage in brewing.
A boiling vessel which has a tangential entry for wort recirculated in the vessel. The circular movement draws trub to the centre allowing a clear wort to be removed from the edge.
A metabolic control in yeast whereby pyruvic acid is converted into ethanol rather than carbon dioxide and water in the presence of oxygen. In many microbes oxygen initiates the Pasteur effect where glucose is digested to carbon dioxide and water.
A traditional continental mashing procedure where amounts of wort are boiled at stages during the mash and returned to the main body to increase the mash temperature in discrete steps. Temperatures increase from 35 to 45 to 65oC so allowing differential digestion of different grain components, particularly glucans, protein and starch respectively due to the different temperature optima of the relevant enzymes. This process is most relevant to the use or poorly modified malt which has been incompletely processed in malting.
Sugars composed of a number of glucose units bonded together. Generally produced by mashing and often containing between four and twenty glucose units and some extent of branching. Dextrins are not fermented by brewing yeast and remain in the beer to provide for the impression of body and mouthfeel.
A distinctive flavour present in some beers and resulting from the chemical conversion of acetolactate metabolic intermediate during fermentation. Levels rise with active yeast growth but decline during maturation when yeast reabsorb diacetyl and reduce it to 2,3 butanediol. Many breweries control diacetyl to non perceptible levels, below 0.2 mg per litre, but higher levels may be acceptable in some beers, particularly British and Scotch ales.
Dimethyl sulphide (DMS)
A distinctive flavour of beer with the character of cooked vegetables, cabbage, sweetcorn or brussel sprouts. Arises from the thermal decomposition during boiling of precursors such as S methyl methionine from malt. DMS is very volatile and will be driven off by the vapours produced in boiling. However, if wort is kept hot for a period after boiling it will accumulate DMS to levels which may be detected in beer (above 90 mg per litre). DMS may also be produced by bacterial contamination and so indicates poor handling.
Dissolved oxygen (DO)
The level of oxygen dissolved in wort or beer. Oxygen is poorly soluble in aqueous liquids and limited amounts will dissolve, generally between 12 and 20 mg per litre depending on temperature. However, only small amounts are needed to oxidize sensitive flavour compounds and oxygen will readily stale wort and beer if introduced.
Low growing hops with heights of around 3 meters compared to the 6 meters of traditional hops. This allows a more efficient cultivation and easier harvesting. First Gold was the initial variety developed but others are now available also with increased disease resistance.
Triticum dicocciodes: one of the major cereal species grown in antiquity. Used in Egyptian and Northern Europe as an ingredient in both baking and brewing but of value for brewing as the grains possess a hull which assists in the clarification of the wort after mashing.
The starch storage part of cereal grains. Consists of many large cells containing starch grains. Malting will soften the cells by digestion of the cell walls and mashing will digest the starch to release simple fermentable sugars and dextrins.
A common and predominant ester produced by yeast metabolism during fermentation and maturation. Results from the combination of acetate and ethanol and has a solvent like flavour.
The dominant reaction of yeast metabolism which produces ethanol and carbon dioxide from glucose. Energy is also produced and used by the cell for growth and multiplication.
A vessel used to contain fermenting wort. Commonly constructed of stainless steel for strength and hygiene but traditionally of slate or copper. Cooling panels or coils are often required to maintain temperature and a means of venting the carbon dioxide produced is essential.
A phenolic compound released by malt and converted to spicy flavours such as vinyl guaiacol by wild yeast. This may be perceived as an off flavour in standard beers but is an important feature of authentic wheat beers.
A means of clarifying worts and beers by passage through a membrane with pores or convoluted layers of fibres or particles. Solid materials such as trub and yeast are retained leaving the liquid clear. Retention depends on the specification of the membrane which can rapidly block if overloaded. Absolute filtration will remove over 99% of particulate material of a set size whilst depth filtration will be less efficient. Cross flow filtration involves the beer flowing across the membrane and is less likely to block.
Processing aids added to wort or beer to assist the flocculation and settlement of solid particles, particularly trub and yeast. Auxiliary finings are typically produced from carageenan seaweed extracts of silicate materials and are commonly used to clarify wort or beer from trub while isinglass finings produced from fish collagen are used to assist yeast settlement.
The first collected wort running from the copper to the fermenter. This fraction is most likely to be contaminated if the wort lines are poorly cleaned and it is common practice in some breweries to recirculate the first worts back into the copper for some minutes to sterilise the lines before collection in the fermenter.
The ability of yeasts to aggregate together and so float or settle rapidly. Flocculation is genetically controlled and is generally initiated towards the end of fermentation when sugar levels are low and alcohol is high. Yeast strains differ in their flocculation ability and so show different abilities to clarify during maturation and stillage in dispense.
The froth produced on the top of beer when dispensed with agitation. Composed of a mixture of protein, polysaccharides and iso humulones it forms a layer of liquid around gas bubbles released from the beer. This layer drains slowly so retaining the bubble shape. Antifoaming materials such as lipids reduce the integrity of the layer and collapse the foam. High levels of protein and bitterness in beer will increase foam levels and foam stability.
One of the first identified varieties of hops. Developed in 1875 by Richard Fuggle it remains an important variety used in traditional British beers.
A cell wall polymer found in cereal grains and released by the malting and mashing processes into wort. It is essentially a plant gum and will act to thicken wort and produce body to beer but also increase filtration time. Mashing procedures may be designed to digest b glucan by employing a b glucanase rest at 35oC where b glucanase enzymes are most active.
A digestive enzyme present in cereal grains which selectively digests b glucan. Well modified barley malt will have activated b glucanases during malting and so have limited b glucan to release in mashing. Poorly modified malt will require a temperature rest at 35oC for b glucanase to digest b glucan.
A storage polysaccharide accumulated in yeast cells towards the end of fermentation. Glycogen provides energy for the cells when they start fermentation after storage. Poor storage conditions will deplete glycogen levels and may compromise fermentation.
Gram negative bacteria
Bacteria which show a pink coloration in the Gram’s bacterial identification stain. This results from their cell wall structure not retaining the initial Gram stain, crystal violet, and showing the second counterstain, saffranin.
Gram positive bacteria
Bacteria which show a purple – violet colouration in the Gram’s bacterial identification stain. This results from their cell wall structure retaining the initial Gram stain, crystal violet.
Gravity of worts and beer
A measure of the density of wort and beer. Commonly measured by the buoyancy of a saccharometer calibrated for sugar solutions against a water density of 1.000. The starting or original gravity of a fermentation is termed the ‘og’ whilst the subsequent gravities are termed the ‘pg’ (present gravity) or ‘sg’ (specific gravity) or eventually, the ‘fg’ (final gravity).
The sum total of dry goods added to the mash tun. Generally composed of barley malts but may also include adjunct cereals such as wheat, rice and maize.
A violent release of gas and beer from a bottle. Normally beer releases its dissolved carbon dioxide slowly when dispensed leaving bubbles within the beer. Under some conditions such as when over carbonated the gas may release at once ejecting the beer at the same time. Specific gushing factors have been identified in malts contaminated with Fusarium moulds.
Calcium sulphate salt. Often added to the grist to provide treatment of the liquor in the mash. The calcium will help precipitate phytate released from the malt while the sulphate will enhance bitterness.
A traditional eastern European hop commonly used in lager beers.
A term used to describe light turbidity in worts and beers. May arise from the presence of protein-tannin particles, from oxalic acid crystals or from microbial contamination. Measured in a haze meter. Levels in beer above 1.0 units are regarded as problematic.
A Scottish term for a medium strength ale, generally with the character of a bitter.
A means of extending the brew length by producing high gravity wort and beer which may be diluted to give a larger volume. Such processes require the use of alcohol tolerant yeasts and careful control to minimise disproportionately produced flavours.
Humulus lupulus: A major brewing ingredient added to boiling wort to produce bitterness and hop aroma. The plant is a perennial climbing herb which may grow to 6 meters in height with clockwise twisting bines. Male and female plants are found but only the female produce cones. These may be fertilized by pollen from the male plants to produce seeds but this is not favoured in continental production although typical of British hops. Adapted into brewing in the last 1,000 years hops are a fundamental feature of contemporary beers providing bitterness from their a acids and aroma from their hydrocarbon and oxidized oils. Leaf hops are commonly compressed before use but retain the structure of the hop cone while pelleted hops are macerated before compression. Hop oils may be added instead of these and are selective extractions of the bitterness and aroma materials.
A vessel used to retain hops as the wort drains from the copper. Additional hops may be added to the wort at this point to provide a specific hop character. Syrup adjuncts may also be added to the hop back as they will dissolve easily in the hot wort but not be caramelised by the heating elements in the copper.
The volatile organic fraction of hops containing most of the aroma flavours of hops. 300 different compounds have been separated in this fraction. Three groups are recognised – hydrocarbons, chemically bound oxygen compounds and chemically bound sulphur compounds.
Waxy materials extracted from hops by organic solvents. The soft resin fraction (those soluble in hexane) contains the a and b acids which are responsible for the bitterness of beer.
Trub material precipitated by the boiling of wort. Consists of a mixture of lipids, proteins and tannins and forms a loose but sticky layer on the bottom of the copper. A good hop break is important in producing a clear beer as incompletely precipitated trub will form hazes later.
The major a acid extracted from hops. Is converted to bitter iso humulone by boiling.
The outer layer of the barley and malt grain. An inert and relatively impermeable layer composed of hard cellulose and polyphenols which remains intact during mashing to form a separation layer during wort collection.
Beer produced by freeze concentration where ice crystals are removed after freezing leaving a stronger beer. Protein is also precipitated by the process which produces a more stable beer with lower flavour.
Yeast attached to support materials within fermenters reactors. This yeast mostly remains in place during fermentation and allows a clearer beer to be produced. It is also more active in its metabolism but is mostly used to mature beer rather than primary fermentation.
A classic British beer developed as an export to overseas colonies and possessing strong bitterness to resist contamination during transit. Reputed as a high alcohol beer with pungent hop character and bitterness today’s examples are lighter versions with an ABV or around 4.0% and a bitterness of only 30IBU. Colour is generally straw or pale amber and final gravity low so giving the beer a light mouthfeel.
A traditional mashing process involving keeping the mash at a single temperature during the mash period. This is typically between 60 and 70oC where amylase activity is maximal. Infusion mashes are usually employed for UK beers produced using well modified malt which has incurred extensive protein and b glucan digestion during malting.
A seaweed extract added to boiling wort to encourage precipitation of proteins at the end of boil. Chrodrus crispus and Gigartina stellata were the species traditionally used intact but extracts may now be taken from other seaweeds including Laminaria and Fucus species.
A collagen extract from sturgeon and other fish swim bladders and used as a fining aid to settle yeast in conditioning of beer and in cask conditioned beer. The natural extract is hydrolysed by acid to release particles of highly positively charged collagen proteins which bind strongly to negatively charged yeast cells. Clarification is also enhanced by the production of a dense mesh work of fibers and cells which settles rapidly under gravity.
A straight sided pressure container for beer dispense. Kegs have a single entry valve with a central tube for exit of the beer and a surrounding collar for entry of pressurised gas to push the beer out. Application of the correct pressure for dispense is important as higher levels can result in gas being absorbed by the beer and fobbing on dispense. Most keg beer is brewery conditioned and stabilized by filtration and/or pasteurisation.
An inert material used to enhance filtration of beer by producing a finely porous cake on a filter membrane. This cake increases in depth as beer is progressively filtered and particles remain entrapped in the cake allowing clear beer to filter through. Keiselguhr is made from the shells of diatoms but other filter aids may be composed of clay or silica hydrogel.
A common acid produced by a variety of yeasts and bacteria. A major spoilage flavour resulting from the growth of lactic acid bacteria in beer and detectable by a yogurt like aroma and taste. Lactic acid bacteria also produce distinctive flavours along with lactic acid, for example the butterscotch flavour diacetyl.
One of the predominant groups of lactic acid bacteria. A number of species including L. brevis, L. delbrueckii and L. pastorianus are contaminants of beer producing lactic acid and other off flavours. Lactic acid bacteria are commonly used in other food fermentations such as yoghurt and sauerkraut.
A rather general term for bottom fermented beers although traditionally used to designate beers matured for long periods at cold temperature. Lager beers today are generally very light in colour, have some dimethyl sulphide aroma and are hoppy and moderately bitter in taste. They are filtered and brewery conditioned to produce a high carbonation and served from kegs through a fawcett.
Beers spontaneously fermented with a complex mixture of moulds, wild yeast and bacteria to produce a sour, cider like flavour. A traditional beer of Belgium with some varieties sweetened with fruits, particularly raspberry and cherry. The complex character changes considerably with age and blendings are often made to produce a balanced beer called Gueuze.
A separating vessel used to sparge a mash and separate clear wort from the residual grains. Differs from a mash tun in being wider with a larger floor area to give a faster run off. Lauter tuns also have stirring rakes to agitate the mash and may be used after the mash has been incubated in a cereal cooker with ajuncts. In this arrangements more mashings may be performed per day so increasing efficiency.
Brewing terminology for water used in brewing. Supply liquor is obtained from local boreholes or direct from water company supplies. Brewing liquor is that used in the process whilst process liquors are used for washing, heating or other activities. The total amount of liquor used in brewing may be between 4 and 10 times the volume of beer produced. Reducing this volume is a major target of increasing efficiency of production and minimising environmental impact.
Low alcohol beer
A beer produced from a low gravity wort and incompletely fermented or from a higher alcohol fermentation but with the alcohol removed by evaporation. Generally brewed for a specific market low alcohol beers lack the complex character of standard beers and are often supplemented with malt and hop extracts to provide additional flavour.
A spicy flavoured component of hop oil.
A major brewing ingredient providing sugars for yeast fermentation. Usually derived from barley although other grains such as wheat, oats and rye may also be malted. Malted grains are softened by enzyme action during malting producing a modified grain. This softening results from digestion of cell wall material and exposes the starch for full digestion in mashing.
A simple microbiological growth media used in the laboratory for yeasts and moulds. Produced by mixing malt extract with up to 2% agar.
Malt production involves steeping the grains in 2 or 3 changes of water for 2-3 days to stimulate germination. Germinating grains are spread on open floors (floor malting), in long Saladin boxes or in automatic vessels with rotating arms mix and control the growth. When the grains have developed sufficiently to produce adequate levels of enzymes they are dried in a kiln. Low temperature drying, less than 120oC, will preserve enzyme activity. Higher temperatures will roast the grain producing flavours but remove enzyme activity.
A major disaccharide sugar produced by digestion of starch in mashing. b amylase specifically hydrolyses the non reducing end of starch chains to release maltose which comprises between 40 and 50% of the total sugar produced by the digestion. Composed of two glucose bound together maltose is readily fermented by yeast.
A major sugar produced by digestion of starch in malting. a amylase releases maltotriose from starch chains by random hydrolysis. Maltotriose is fermentable by most brewing yeast but this depends on the health of the yeast. Old, stressed or continually repitched yeast may be less efficient at fermenting maltotriose and so leave the beer with an incomplete fermentation and an undesirably high final gravity.
The first major stage in the brewing process where malt and liquor are mixed and left to incubate at set temperature(s). Starch is digested to simple sugars and many compounds are released from the malt to enrich the wort. Infusion mashing maintains a constant temperature, generally between 60 and 68oC while temperature programmed and decoction mashing increases the temperature in steps from 35 oC to 45 oC to
65 oC and finishing at 75oC to curtain enzyme activity. Temperature programmed mashing is most suitable for poorly modified malt and allows rests at temperatures optimal for the digestion of b glucans, protein and starch respectively.
A large scale means of separating the mash solids from the wort at the end of mashing. Mash filters compress the mash in a large press allowing wort through filter cloth and retaining solids. Extraction of sugars may be more efficient than standard mash tun separation but the wort may be cloudier. Really only applicable to bulk production due to the high capital cost of the equipment.
Darkly pigmented compounds produced by the combination of simple sugars and amino acids. This reaction is accelerated by heating and mostly occurs during boiling. A range of melanoidins is produced from the different sugars and amino acids in the wort and also depends on the time of boiling. Melanoidins are good oxygen scavengers and can protect wort against oxidation and staling.
Distinctive flavour compounds with the aroma of skunk. Produced by the photolysis of a side chain of iso a acids and the subsequent reaction of this with sulphur containing thiol radicals to produce 3-methyl-2-butene-1-thiol. Exposing beer to light, particularly by using clear glass bottles, will initiate this reaction although specially treated hop oil, Tetra hop, will stabilise the iso a acid.
A distinctive British beer with low hop character typically drunk in the north and for some time the dominant ale in England. Traditional versions were brewed with dark malts to give a caramel and liquorice character and a solid body. Current examples are low in gravity and alcohol and some lack the dark malts and are low gravity bitters. ABV is between 3.1 and 4.8%, bitterness around 22 and colour 85 but sometimes up to 200 EBC. A few strong varieties with ABV up to 6.0 are closer to some original milds.
Milling crushes grains before mashing and so exposes the internal contents to the mash liquor and enhances dissolving and digestion by enzymes. Mills crush grain between two, four or six rollers running in opposite directions and are set to break open the grain but not to crush it into flour. Part crushing is particularly important to ensure that the husk is retained to provide the filter bed for separating wort at the end of mashing.
The addition of nitrogen gas to beer to produce a smoother palate on dispense. Nitrogen is poorly soluble in beer and requires a high pressure to dissolve. On dispense much of the gas leaves the beer producing small bubbles which provide a tight, compact head.
Potentially carcinogenic compounds produced from amides or amines in wort, usually by bacterial action. Levels are low today due to control over the brewing process and reduction in microbial contamination.
A ancillary grain used in some beers to give a malty character and smooth mouthfeel.
A traditional British beer with high alcohol levels and rich and complex flavours. Traditionally dark and well matured, often a seasonal winter brew. ABV is between 4.3 and 12%, bitterness around 29 and colour 70 but sometimes up to 220EBC.
An organic acid released into wort from barley and other grains. Can complex with calcium to produce precipitated crystals of calcium oxalate.
A protease enzyme produced by the pineapple plant. May be used in beer to reduce protein levels and protect against haze.
Paraflow heat exchangers are used to heat or cool bulk volumes of beer. They are typically constructed of a series of parallel plates of stainless steel with wort or beer running across one side and chilled water or steam across the other. The rate of heat exchange is a function of the flow rate of the product passing through.
The heat treatment of beer to kill microorganisms and provide stability to brewery processed beer. Flash pasteurisation is commonly conducted by passing beer through a heat exchanger heated with steam. The rapid flow of the beer ensures a limited time of contact of around 30 seconds at a temperature of 73oC and minimises degradative effects on the beer. Despite this pasteurised beer often tastes oxidised and aged due to the oxidisation of components at the high temperatures. Pasteurisation is measured in pasteurising units (PU) which are defined as the effect on microorganisms of holding the beer at 60oC for one minute.
A coccus variety of lactic acid bacteria with the ability to produce high levels of lactic acid and so readily spoil wort and beer. As with all lactic acid bacteria Pediococci are non-spore forming and gram negative. Unlike other lactic acid bacteria they are spherical in shape and are often distinguished by their diploid or tetrad arrangements of cells.
Permanently soluble nitrogen
The fraction of protein and other nitrogen compounds remaining after precipitation in the boil. These proteins will contribute to head formation and to mouthfeel and are an important component of beer.
Cyclic organic compounds present in wort and often possessing distinctive flavours. Aromatic alcohol phenols are produced by yeast fermentation and may give beer a floral character above 200 mg per litre. Other phenols are less attractive. Chlorophenols produced by the reaction of phenol with chlorine are very pungently medicinal at very low levels. Spicy, clove like flavours are produced by the decarboxylation of the phenol ferulic acid from malt into 4-vinyl guaiacol. This reaction is catalysed by wild yeasts but not brewing yeasts and indicates possible contamination of yeast or beer. It is, however, a desirable feature of wheat beers which thus require an appropriate yeast for an authentic production.
A classic continental beer using Saaz or Hallertau hops to provide a distinctive flowery aroma. The beer is a golden and aromatic lager with a dry finish originating from the Czech town of Plzen but now found throughout Germany and internationally.
Plato – degrees of measurement
Plato units relate wort strength to the concentration of sugar in solution rather than the density. 1o Plato is equivalent to 1 gram of sucrose dissolved in distilled water. For comparison a wort with a specific gravity of 1040 will be 10o Plato.
Polymerase chain reaction (PCR)
A molecular biology procedure whereby a single piece of DNA may be extracted from a sample and multiplied extensively to demonstrate the presence of a particular gene or organism. Currently being developed as an identification procedure for yeasts and beer contaminants but also to distinguish barley and hop varieties.
A distinctive type of British beer developed as a mixture of different beers. Typically characterised by a balance of malt, roast, hop, bitterness, fruit and spicy flavours. Traditionally with the harsh burnt taste of brown malt many current versions have a full body with roast malt in the aftertaste. ABV is between 3.8 and 6.1%, bitterness around 33 and colour 120 but sometimes up to 300EBC.
Sugars added to beer after fermentation to restart yeast activity and fermentation. Important in some cask ales and bottle conditioned beers where a secondary fermentation is necessary to produce additional carbonation. Sucrose would commonly be used but malt gives a better flavour profile.
Enzymes found in malt which digest proteins into polypeptides and amino acids. They are very active in malting where much of the barley protein is digested. In poorly modified malt it may be necessary to further digest protein in mashing by a temperature infusion at 50-55oC to avoid beer hazes from excess protein remaining in the wort.
Phenolic compounds produced by the oxidation of polyphenols. Can act as oxidising agents themselves in wort and so produce stale flavours.
A peculiarly distinctive German beer with a rich smoky flavour produced by the use of malt dried in the smoke of moist beechwood fires. Generally dark in colour and bottom fermented.
A term for cask ale – beer which undergoes a secondary conditioning after the primary fermentation. This conditioning typically takes place in a cask or bottle which thus contains live yeast.
The genus of yeast which are particularly adapted to fermentation of strong sugar solutions and which thus produce high levels of alcohol. Saccharomyces cereisiae is the traditional brewing yeast and produces the typical flavour balance characteristic of beer. Other Saccharomyces yeasts also ferment but produce high levels of other flavours such as the spicy 4-vinyl guaiacol or the butterscotch diacetyl which are not so desirable. These Saccharomyces yeasts would be considered contaminants and may be termed wild yeasts. Saccharomyces diastaticus is a particularly undesirable contaminant in that it has the ability to ferment dextrins by producing amylase enzymes. As a result the beer becomes over fermented and lacks the body provided by the unfermentable sugars.
A bulk container for the semi automatic malting of cereals. Barley grains are placed in the box immediately after steeping and grow. Air is sparged through the floor of the box and rakes are slowly run through the box turning the grains and keeping the rootlets from entangling.
National beers brewed in Scotland are less hoppy and maltier than other British beers and may have a sweeter taste due to a higher finishing gravity. Diacetyl may be more apparent on these beers complimenting the malt character. Light, heavy and special or export designate the increasing strengths.
The wooden plug sealing the top of a cask. The shive contains a central plug which is opened to the air before dispense. Wooden pegs called spiles are inserted in the centre of the shive to control air inlet and gas release from the beer. Porous spiles allow air through but reduce contamination from particles and are used during the serving period. Impermeable, hard spiles are used to temporarily seal the cask between serving periods.
Commonly known as lucilite, silica hydrogel specifically absorbs proteins and polypeptides from wort. The particles are added to beer during maturation or at filtration and can act in as little as 5 minutes to adsorb polypeptides with an isoelectric point between 3.0 and 5.0. As a result they are used in clarification and stabilisation, particularly when a long shelf life is required.
Malt which has absorbed water and become soft and stale.
Washing of grains at the end of mashing to remove residual sugars and
maximise extract. Ideally using treated liquor at 77oC to reduce
viscosity and terminate enzyme activity. Sparging liquor should be
added as a fine spray to the grain bed to avoid disturbance of the
The solids remaining at the end of sparging. Consisting of husks, barley embryo, roots and shoots, undissolved starch grains and precipitated proteins and tannins. Spent grains are typically used as animal feed or for composting but may have occasional uses in foods such as biscuits.
The major storage polysaccharide in barley endosperm cells. Produced by the polymerisation of glucose molecules starch has two molecular species, the linear polymer amylase (around 20%) and the branched polymer amylopectin (around 80%). Starch molecules are condensed into rigid starch grains during growth of the barley grain. These grains provide an inert energy store for when the grain germinates and are of two types, small grains 1-5m diameter and large grains 10-25m diameter. Mashing rapidly dissolves the small grains but most dissolved starch derives from the larger grains.
Lipids which are essential for yeast membrane growth. Sterols contribute to the flexibility of yeast membranes and require oxygen for their synthesis by the yeast cell. Although yeast may multiply extensively without oxygen during fermentation they must be exposed to oxygen before a further pitching so that they have an opportunity to produce sterols. This will typically happen during cropping but many brewers aerate their collected worts before fermentation to ensure that their yeast is fully prepared.
A support for casks when positioned in the cellar. Stillaging is necessary so that yeast may settle into the belly of the cask and not be pulled out into the beer when it is dispensed through the tap. Stillages are usually two bars of wood or steel with the rear bar raised slightly higher than the front bar. The cask is further raised during dispense by placing chocks under the rear edge to assist flow.
A distinctive type of British beer developed as a strong version of Porter. Characterised by a strong roast flavour due to the use of roast barley grains stout was initially a high alcohol beer with a rich aroma and strong burnt taste. Today many versions are lower in strength and have less harsh character. Variations exist with added sweetness through the use of lactose (milk stout) or of shellfish (oyster stout) and with very high alcohol levels (Imperial stout). ABV is between 4.0 and 5.3%, bitterness around 34 and colour 130 but sometimes up to 280EBC.
The temperature of the brewing liquor which is added to the mash. This is typically between 75 and 80oC to compensate for the lower temperature of the mash and adjusted to achieve a final temperature in the mash of 60-70oC. A high strike temperature is also desirable to swell and gelatinise the starch grains and so expose them to digestive amylase enzymes.
Common table sugar, sucrose is a disaccharide composed of molecules of glucose and of fructose bonded together. Only small amounts (<5%) of sucrose are found in malt but sucrose may be added to wort as an adjunct and after fermentation as a priming sugar to restart fermentation.
Beer which has been photolysed by light. The photolysis releases a side chain of iso a acids and the subsequent reaction of this with sulphur containing thiol radicals to produce 3-methyl-2-butene-1-thiol which has the characteristic smell of skunk (also shown by grass snakes).
Temperature programmed mashing
A mashing regime which involves a stepped increase in temperature during the mash. Typical steps involve one temperature stands at 35-40 oC for digestion of b glucans, another at 50 oC for digestion of proteins, a third at 65 oC for digestion of starch and a final rise to a 75oC mash-off to stop enzyme activity by denaturation.
The inner of three protective layers around the barley grain and composing the husk.
Top fermenting yeast
Yeasts which rise to the top of the wort during fermentation. These yeasts remain on the surface as a yeast head and may be skimmed for repitching in a future brew. In general ale yeasts are top fermenting whilst lager yeasts are bottom fermenting.
A storage sugar found in yeast and providing energy reserves and stress protection. High levels (15% of dry weight) may develop towards the end of fermentation in preparation for dormancy before the next exposure to sugars and subsequent fermentation. Trehalose acts like glycogen in providing readily available energy but is unique in becoming intimately associated with cell membranes to stabilize them against stress conditions such as high temperature, high ethanol levels and desiccation.
Precipitated proteins, tannins and lipids produced in hot wort during
boiling and in cold wort after collection in the fermenter. Ideally
should be left behind in the copper and fermenter when wort and beer
are racked to another vessel as may cause haze and encourage microbial
A fermentation vessel which may also be used for conditioning. Common in large scale production.
Removal of alcohols from beer by means of exposure to low pressures and enhanced evaporation of volatile compounds.
A test of yeast functioning which measures the metabolic ability of yeast. Tests use the rate of uptake of oxygen when fermenting sugars or the release of acid and reduction in pH as an index of vitality. The higher the vitality the better the yeast’s fermentative potential.
Vicinyl diketones (VDK)
Molecules with a double aldehyde group produced during fermentation by nitrogen metabolism. The common VDK is diacetyl produced from acetolactate, an intermediate of valine metabolism. Acetolactate is released into the wort and decarboxylates to diacetyl which has a very strong butterscotch flavour at low concentrations. Levels rise towards the end of fermentation but diacetyl is then reduced by yeast to produce 2,3 butane diol, a compound with a much higher flavour threshold. These reactions occur during normal processing but if yeast is removed too early high levels of diacetyl may result in beer.
An agar medium used for the laboratory growth and characterisation of yeasts. Wallerstein nutrient agar (WLN) contains bromomethyl green dye which may be taken up to different extents by different yeast strains so distinguishing their colonies. Wallerstein differential agar (WLD) also contains actinomycin, an antibiotic which inhibits yeast growth. WLD media is used to show the presence of bacteria in a beer or wort sample.
Treatments to adjust and control the acidity of the mash, usually by the addition of acid to neutralise the bicarbonate salts and by addition of calcium salts to enhance the release of acid from phytate. Typical treatments may be to add sulphuric acid to the hot liquor followed by a mixture of calcium sulphate and calcium chloride to the mash.
A device inserted into a beer can to induce the rapid release of nitrogen gas when the pressure is release on opening. The rapid release results in many small bubbles which form a thick, creamy head which lasts longer than a carbon dioxide head.
Non brewing yeasts are commonly called wild. Even non brewing strains of Saccharomyces cerevisiae may be termed wild in a brewery if they alter the beer flavour or affect the fermentation performance of the standard brewing yeast. Most wild yeasts found in beer are of a different Saccharomyces species or a different genera such as Pichia, Bretannomyces or Hansenula and produce distinctive flavours as well as turbidity.
The sugar solution produced by the mashing process. Wort also contains proteins, amino acids, phenols, vitamins and minerals and is an excellent medium for the growth of microorganisms. The major sugar in most worts is maltose (40-45%) but glucose (12%), maltotriose (15%) and dextrins (20-25%) are also present.
The basic sugar of pentosan compounds found in malt cell walls. Pentosans are not easily digested but those that are will release xylose into the wort.
A microscopic fungus. Over 700 species are recognised but all share a common single celled morphology with a rigid cell wall and an eukaryotic cell structure. Most yeasts reproduce by budding and many produce spores which help resist adverse conditions. The common brewing yeast is the species Saccharomyces cerevisiae which has the ability to ferment high sugar concentrations and may be distinguished by this in identification tests.
The standard measurement of packaged hops. One zentner of whole leaf hops is equivalent to 50Kg.
A pernicious bacterial contaminant of beer. Zymonomas mobilis is the major species found and produces very distinctive vegetal off flavours as well as some lactic acid so rapidly spoiling beer. The bacteria grows particularly well with glucose and sucrose and is most likely to contaminate primings or beer primed for cask conditioning.Return to Brewlab blog