Brewing is the production of beer through steeping a starch source (commonly cereal grains) in water and then fermenting with yeast. Brewing has taken place since

History of beer

Beer is one of the world's oldest beverages, with the history of beer dating back to 6000 BC, and being recorded in the written history of Ancient Iraq. The earliest Sumerian writings contain references to beer...

 around the 6th millennium BCE, and archeological evidence suggests that this technique was used in ancient Egypt

History of Egypt

Egyptian history can be roughly divided into the following periods:*Prehistoric Egypt*Ancient Egypt**Early Dynastic Period of Egypt: 31st to 27th centuries BC**Old Kingdom of Egypt: 27th to 22nd centuries BC...

. Descriptions of various beer recipes can be found in Sumer

Sumer

Sumer was a civilization and historical region in southern Mesopotamia, modern Iraq during the Chalcolithic and Early Bronze Age....

ian writings, some of the oldest known writing of any sort. Brewing takes place in a brewery by a brewer, and the brewing industry is part of most western economies.

The basic ingredients of beer are water; a fermentable (convertible into alcohol) starch source, such as malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

ed barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

; a brewer's yeast to produce the fermentation; and a flavouring, such as hops

Hops

Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...

. A secondary starch source (an adjunct) may be used, such as maize (corn), rice or sugar. Less widely used starch sources include millet

Millet

The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...

, sorghum

Sorghum

Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...

 and cassava

Cassava

Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...

 root in Africa, potato in Brazil, and agave

Agave

Agave is a genus of monocots. The plants are perennial, but each rosette flowers once and then dies ; they are commonly known as the century plant....

 in Mexico, among others. The amount of each starch source in a beer recipe is collectively called the grain bill.

There are several steps in the brewing process, which include malting, milling

Mill (grinding)

A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal , wind or water...

, mashing, lautering, boiling, fermenting

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

, conditioning, filtering, and packaging. There are three main fermentation methods, warm, cool and wild or spontaneous. Fermentation may take place in open or closed vessels. There may be a secondary fermentation which can take place in the brewery, in the cask

Cask ale

Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer which is conditioned and served from a cask without additional nitrogen or carbon dioxide pressure...

 or in the bottle

Bottle conditioning

Bottle conditioned beers are either unfiltered so the final conditioning of the beer takes place in the bottle, or filtered and then reseeded with yeast so that an additional fermentation may take place.-Priming:...

.

Brewing specifically refers to the process of steeping, such as with making tea, sake and soy sauce

Soy sauce

Soy sauce is a condiment produced by fermenting soybeans with Aspergillus oryzae or Aspergillus sojae molds, along with water and salt...

. Wine and cider

Cider

Cider or cyder is a fermented alcoholic beverage made from apple juice. Cider varies in alcohol content from 2% abv to 8.5% abv or more in traditional English ciders. In some regions, such as Germany and America, cider may be termed "apple wine"...

 technically aren't brewed, rather vinted, as the entire fruit is pressed, and then the liquid extracted. Mead

Mead

Mead , also called honey wine, is an alcoholic beverage that is produced by fermenting a solution of honey and water. It may also be produced by fermenting a solution of water and honey with grain mash, which is strained immediately after fermentation...

 isn't technically brewed, as the honey is used entirely, as opposed to being steeped in water.

Ingredients

The basic ingredients of beer are water; a starch source, such as malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

ed barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

, able to be fermented (converted into alcohol); a brewer's yeast to produce the fermentation; and a flavouring such as hops

Hops

Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...

. A mixture of starch sources may be used, with a secondary starch source, such as maize (corn), rice or sugar, often being termed an adjunct, especially when used as a lower-cost substitute for malted barley. Less widely used starch sources include millet

Millet

The millets are a group of small-seeded species of cereal crops or grains, widely grown around the world for food and fodder. They do not form a taxonomic group, but rather a functional or agronomic one. Their essential similarities are that they are small-seeded grasses grown in difficult...

, sorghum

Sorghum

Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...

 and cassava

Cassava

Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...

 root in Africa, potato in Brazil, and agave

Agave

Agave is a genus of monocots. The plants are perennial, but each rosette flowers once and then dies ; they are commonly known as the century plant....

 in Mexico, among others. The amount of each starch source in a beer recipe is collectively called the grain bill.

Water
Beer is composed mostly of water. Regions have water with different mineral components; as a result, different regions were originally better suited to making certain types of beer, thus giving them a regional character. For example, Dublin has hard water

Hard water

Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...

 well suited to making stout

Stout

Stout is a dark beer made using roasted malt or barley, hops, water and yeast. Stouts were traditionally the generic term for the strongest or stoutest porters, typically 7% or 8%, produced by a brewery....

, such as Guinness

Guinness

Guinness is a popular Irish dry stout that originated in the brewery of Arthur Guinness at St. James's Gate, Dublin. Guinness is directly descended from the porter style that originated in London in the early 18th century and is one of the most successful beer brands worldwide, brewed in almost...

; while Pilsen has soft water well suited to making pale lager

Pale lager

Pale lager is a very pale to golden-coloured beer with a well attenuated body and a varying degree of noble hop bitterness. The brewing process for this beer developed in the mid 19th century when Gabriel Sedlmayr took pale ale brewing techniques back to the Spaten Brewery in Germany and applied it...

, such as Pilsner Urquell

Pilsner Urquell

Plzeňský Prazdroj , known better by its German name Pilsner Urquell , is a bottom-fermented beer produced since 1842 in Pilsen, part of today's Czech Republic. Pilsner Urquell was the first pilsner beer in the world...

. The waters of Burton in England contain gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

, which benefits making pale ale

Pale ale

Pale ale is a beer which uses a warm fermentation and predominantly pale malt. It is one of the world's major beer styles.The higher proportion of pale malts results in a lighter colour. The term "pale ale" was being applied around 1703 for beers made from malts dried with coke, which resulted in a...

 to such a degree that brewers of pale ales will add gypsum to the local water in a process known as Burtonisation.

Starch source

The starch source in a beer provides the fermentable material and is a key determinant of the strength and flavour of the beer. The most common starch source used in beer is malted grain. Grain is malted by soaking it in water, allowing it to begin germination

Germination

Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...

, and then drying the partially germinated grain in a kiln. Malting grain produces enzymes that convert starches in the grain into fermentable sugars. Different roasting times and temperatures are used to produce different colours of malt from the same grain. Darker malts will produce darker beers.

Nearly all beer includes barley malt as the majority of the starch. This is because of its fibrous husk, which is not only important in the sparging stage of brewing (in which water is washed over the mashed

Mashing

In brewing and distilling, mashing is the process of combining a mix of milled grain , known as the "grain bill", and water, known as "liquor", and heating this mixture...

 barley grains to form the wort

Wort (brewing)

Wort, , is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars that will be fermented by the brewing yeast to produce alcohol.- Production :...

), but also as a rich source of amylase

Amylase

Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...

, a digestive

Digestion

Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

 enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 which facilitates conversion of starch into sugars. Other malted and unmalted grains (including wheat, rice, oats, and rye

Rye

Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...

, and less frequently, corn and sorghum) may be used. In recent years, a few brewers have produced gluten-free beer made with sorghum with no barley malt for people who cannot digest gluten

Gluten

Gluten is a protein composite found in foods processed from wheat and related grain species, including barley and rye...

-containing grains like wheat, barley, and rye.

Hops

Flavouring beer is the sole major commercial use of hops. The flower of the hop vine

Hop (plant)

Humulus, Hop, is a small genus of flowering plants native to temperate regions of the Northern Hemisphere. The female flowers of H. lupulus are known as hops, and are used as a culinary flavoring and stabilizer, especially in the brewing of beer...

 is used as a flavouring and preservative agent in nearly all beer made today. The flowers themselves are often called "hops".
Hops were used by monastery breweries, such as Corvey in Westphalia, Germany, from 822 AD, though the date normally given for widespread cultivation of hops for use in beer is the thirteenth century. Before the thirteenth century, and until the sixteenth century, during which hops took over as the dominant flavouring, beer was flavoured with other plants; for instance, Glechoma hederacea. Combinations of various aromatic herbs, berries, and even ingredients like wormwood would be combined into a mixture known as gruit

Gruit

Gruit is an old-fashioned herb mixture used for bittering and flavoring beer, popular before the extensive use of hops. Gruit or grut ale may also refer to the beverage produced using gruit....

 and used as hops are now used. Some beers today, such as Fraoch' by the Scottish Heather Ales company and Cervoise Lancelot by the French Brasserie-Lancelot company, use plants other than hops for flavouring.

Hops contain several characteristics that brewers desire in beer. They contribute a bitterness that balances the sweetness of the malt; the bitterness of beers is measured on the International Bitterness Units scale. Hops contribute floral, citrus, and herbal aromas and flavours to beer. They also have an antibiotic

Antibiotic

An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...

 effect that favours the activity of brewer's yeast over less desirable microorganisms, and hops aids in "head retention", the length of time that a foamy head created by carbonation will last. The acidity of hops is a preservative.

Yeast

Yeast is the microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

 that is responsible for fermentation in beer. Yeast metabolises

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 the sugars extracted from grains, which produces alcohol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 and carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, and thereby turns wort

Wort (brewing)

Wort, , is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars that will be fermented by the brewing yeast to produce alcohol.- Production :...

 into beer. In addition to fermenting the beer, yeast influences the character and flavour.
The dominant types of yeast used to make beer are Saccharomyces cerevisiae

Saccharomyces cerevisiae

Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...

, known as ale yeast, and Saccharomyces uvarum, known as lager yeast; their use distinguishes ale

Ale

Ale is a type of beer brewed from malted barley using a warm fermentation with a strain of brewers' yeast. The yeast will ferment the beer quickly, giving it a sweet, full bodied and fruity taste...

 and lager

Pale lager

Pale lager is a very pale to golden-coloured beer with a well attenuated body and a varying degree of noble hop bitterness. The brewing process for this beer developed in the mid 19th century when Gabriel Sedlmayr took pale ale brewing techniques back to the Spaten Brewery in Germany and applied it...

. Brettanomyces

Brettanomyces

Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of...

ferments lambic

Lambic

Lambic is a very distinctive type of beer brewed only in the Pajottenland region of Belgium and in Brussels itself at the Cantillon Brewery and museum...

s, and Torulaspora delbrueckii

Torulaspora delbrueckii

Torulaspora delbrueckii is a yeast species which is also known as Saccharomyces delbrueckii or Saccharomyces rosei .The genetic analyses have revealed that the various strains treated as T...

ferments Bavarian weissbier

Weissbier

Weissbier , also known as Weizenbier , is a Bavarian specialty beer in which a significant proportion of malted barley is replaced with malted wheat: a wheat beer. By German law, Weissbiers brewed in Germany must be top-fermented...

.
Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts. A few styles such as lambics rely on this method today, but most modern fermentation adds pure yeast cultures

Microbiological culture

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...

.

Clarifying agent

Some brewers add one or more clarifying agents to beer, which typically precipitate (collect as a solid) out of the beer along with protein solids and are found only in trace amounts in the finished product. This process makes the beer appear bright and clean, rather than the cloudy appearance of ethnic and older styles of beer such as wheat beer

Wheat beer

Wheat beer is a beer that is brewed with a large proportion of wheat. Wheat beers often also contain a significant proportion of malted barley. Wheat beers are usually top-fermented...

s.

Examples of clarifying agents include isinglass

Isinglass

Isinglass is a substance obtained from the dried swim bladders of fish. It is a form of collagen used mainly for the clarification of wine and beer. It can also be cooked into a paste for specialized gluing purposes....

, obtained from swimbladders of fish; Irish moss, a seaweed; kappa carrageenan

Carrageenan

Carrageenans or carrageenins are a family of linear sulfated polysaccharides that are extracted from red seaweeds. There are several varieties of carrageen used in cooking and baking. Kappa-carrageenan is used mostly in breading and batter due to its gelling nature...

, from the seaweed Kappaphycus cottonii

Kappaphycus cottonii

Kappaphycus alvarezii is a species of red alga. It is one of the most important commercial sources of carrageenans, a family of gel-forming, viscosifying polysaccharides. Farming methods affect the character of the carrageenan that can be extracted from the seaweed.This alga grows to two meters...

; Polyclar (artificial); and gelatin

Gelatin

Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...

. If a beer is marked "suitable for Vegans", it was generally clarified either with seaweed or with artificial agents, although the Fast Cask method invented by Marston's in 2009 may provide another method.

Brewing process

All beers are brewed using a process based on a simple formula. Key to the process is malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

ed grain

Cereal

Cereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...

 – mainly barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

, though other cereals, such as wheat or rice, may be added. Malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

 is made by allowing a grain to germinate

Germination

Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...

, after which it is then dried in a kiln

Kiln

A kiln is a thermally insulated chamber, or oven, in which a controlled temperature regime is produced. Uses include the hardening, burning or drying of materials...

 and sometimes roasted. The germination process creates a number of enzymes, notably α-amylase and β-amylase, which convert the starch in the grain into sugar. Depending on the amount of roasting, the malt will take on a dark colour and strongly influence the colour and flavour of the beer. The malt is crushed to break apart the grain kernels, expose the cotyledon which contains the majority of the carbohydrates and sugars, increase their surface area, and separate the smaller pieces from the husks.

There are several steps in the brewing process, which include malting, milling

Mill (grinding)

A grinding mill is a unit operation designed to break a solid material into smaller pieces. There are many different types of grinding mills and many types of materials processed in them. Historically mills were powered by hand , working animal , wind or water...

, mashing

Mashing

In brewing and distilling, mashing is the process of combining a mix of milled grain , known as the "grain bill", and water, known as "liquor", and heating this mixture...

, lautering

Lautering

Lautering is a process in brewing beer in which the mash is separated into the clear liquid wort and the residual grain. Lautering usually consists of 3 steps: mashout, recirculation, and sparging.-Mashout:...

, boiling, fermenting

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

, conditioning, filtering, and packaging.

Malting is the process where the barley grain is made ready for brewing. Malting is broken down into three steps, which help to release the starches in the barley. First, during steeping

Steeping

Steeping or weltering may mean:# Saturation in a liquid solvent to extract a soluble ingredient, where the solvent is the desired product. Tea is prepared for drinking by steeping the leaves in heated water to release the flavor and nutrients...

, the grain is added to a vat with water and allowed to soak for approximately 40 hours. During germination, the grain is spread out on the floor of the germination room for around 5 days. The goal of germination is to allow the starches in the barley grain to breakdown into shorter lengths. When this step is complete, the grain is referred to as green malt. The final part of malting is kilning. Here, the green malt goes through a very high temperature drying in a kiln. The temperature change is gradual so as not to disturb or damage the enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s in the grain. When kilning is complete, there is a finished malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

 as a product.

The next step in the brewing process is milling. This is when the grains that are going to be used in a batch of beer are cracked. Milling the grains makes it easier for them to absorb the water that they are mixed with and which extracts sugars from the malt. Milling can also influence the general characteristics of a beer.

Mashing is the next step in the process. This process converts the starches released during the malting stage, into sugars that can be fermented. The milled grain is mixed with hot water in a large vessel known as a mash tun. In this vessel, the grain and water are mixed together to create a cereal mash. During the mash, naturally occurring enzymes present in the malt convert the starches (long chain carbohydrates) in the grain into smaller molecules or simple sugars (mono-, di-, and tri-saccharides). This "conversion" is called saccharification.
The result of the mashing process is a sugar rich liquid or "wort" , which is then strained through the bottom of the mash tun in a process known as lautering

Lautering

Lautering is a process in brewing beer in which the mash is separated into the clear liquid wort and the residual grain. Lautering usually consists of 3 steps: mashout, recirculation, and sparging.-Mashout:...

. Prior to lautering, the mash temperature may be raised to about 75 °C (165–170 °F) (known as a mashout) to deactivate enzymes. Additional water may be sprinkled on the grains to extract additional sugars (a process known as sparging).

At this point the liquid is known as wort

Wort (brewing)

Wort, , is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars that will be fermented by the brewing yeast to produce alcohol.- Production :...

. The wort is moved into a large tank known as a "copper" or kettle

Kettle

A kettle, sometimes called a tea kettle or teakettle, is a small kitchen appliance used for boiling water. Kettles can be heated either by placing on a stove, or by their own electric heating element.- Stovetop kettles :...

 where it is boiled with hops

Hops

Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...

 and sometimes other ingredients such as herbs or sugars. This stage is where many chemical and technical reactions take place, and where important decisions about the flavour, colour, and aroma of the beer are made. The boiling process serves to terminate enzymatic processes, precipitate

Precipitation (chemistry)

Precipitation is the formation of a solid in a solution or inside anothersolid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, or when compacted by a centrifuge, a pellet. The liquid remaining above the solid...

 proteins, isomerize hop resin

Resin

Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...

s, and concentrate and sterilize

Sterilization (microbiology)

Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

 the wort. Hops add flavour, aroma

Odor

An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...

 and bitterness to the beer. At the end of the boil, the hopped wort settles to clarify in a vessel called a "whirlpool", where the more solid particles in the wort are separated out.

After the whirlpool, the wort then begins the process of cooling. This is when the wort is transferred rapidly from the whirlpool or brew kettle to a heat exchanger

Heat exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

 to be cooled. The heat exchanger consists of tubing inside a tub of cold water. It is very important to quickly cool the wort to a level where yeast can be added safely. Yeast is unable to grow in high temperatures.

After the wort goes through the heat exchanger, the cooled wort goes into a fermentation tank. A type of yeast is selected and added, or "pitched", to the fermentation tank. When the yeast is added to the wort, the fermenting process begins, where the sugars turn into alcohol, carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and other components.

The second to last stage in the brewing process is called racking. This is when the brewer racks the beer into a new tank, called a conditioning tank. Conditioning of the beer is the process in which the beer ages, the flavour becomes smoother, and flavours that are unwanted dissipate.

After one to three weeks, the fresh (or "green") beer is run off into conditioning tanks. After conditioning for a week to several months, the beer enters the finishing stage. Here, beers that require filtration

Filtration

Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...

 are filtered, and given their natural polish and colour. Filtration also helps to stabilize the flavour of the beer. After the beer is filtered, it undergoes carbonation

Carbonation

Carbonation is the process of dissolving carbon dioxide in water. The process usually involves carbon dioxide under high pressure. When the pressure is reduced, the carbon dioxide is released from the solution as small bubbles, which cause the solution to "fizz." This effect is seen in carbonated...

, and is then moved to a holding tank until bottling.

Mashing

Mashing is the process of combining a mix of milled grain (typically malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

ed barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

 with supplementary grains

Adjuncts

Adjuncts are unmalted grains used in brewing beer which supplement the main mash ingredient , often with the intention of cutting costs, but sometimes to create an additional feature, such as better foam retention.- Definition :Ingredients which are standard for certain beers, such as wheat in a...

 such as corn

Maize

Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

, sorghum

Sorghum

Sorghum is a genus of numerous species of grasses, one of which is raised for grain and many of which are used as fodder plants either cultivated or as part of pasture. The plants are cultivated in warmer climates worldwide. Species are native to tropical and subtropical regions of all continents...

, rye

Rye

Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...

 or wheat), known as the "grain bill", and water, known as "liquor", and heating this mixture in a vessel called a "mash tun". Mashing allows the enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s in the malt to break down the starch

Starch

Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

 in the grain into sugars, typically maltose

Maltose

Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....

 to create a malty liquid called wort

Wort

Wort may refer to:* Wort, the liquid created by the mashing of malted barley to use in brewing beer* Worting, Hampshire, a large district and suburb of the town of Basingstoke, in Hampshire, England....

. There are two main methods – infusion

Infusion

An infusion is the outcome of steeping plants with desired chemical compounds or flavors in water or oil.-History:The first recorded use of essential oils was in the 10th or 11th century by the Persian polymath Avicenna, possibly in The Canon of Medicine.-Preparation techniques:An infusion is very...

 mashing, in which the grains are heated in one vessel; and decoction

Decoction

Decoction is a method of extraction, by boiling, of dissolved chemicals, or herbal or plant material, which may include stems, roots, bark and rhizomes. Decoction involves first mashing, and then boiling in water to extract oils, volatile organic compounds, and other chemical substances...

 mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature. Mashing involves pauses at certain temperatures (notably 45 °C, 62 °C and 73 °C), and takes place in a "mash tun" – an insulated brewing vessel with a false bottom

False bottom

A false bottom is an internal partition in a container, typically at the bottom of a drawer, suitcase or similar item, enabling the concealment of objects from a cursory examination of the item's contents...

. The end product of mashing is called a "mash".

Mashing usually takes 1 to 2 hours, and during this time the various temperature rests activate different enzymes depending upon the type of malt being used, its modification level, and the intention of the brewer. The activity of these enzymes convert the starches of the grains to dextrin

Dextrin

Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....

s and then to fermentable sugars such as maltose

Maltose

Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....

. A mash rest from 49–55 °C (120.2–131 F) activates various protease

Protease

A protease is any enzyme that conducts proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the protein....

s, which break down proteins that might otherwise cause the beer to be hazy. This rest is generally used only with undermodified (i.e. undermalted) malts which are decreasingly popular in Germany and the Czech Republic, or non-malted grains such as corn

Maize

Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 and rice, which are widely used in North American beers. A mash rest at 60 °C (140 °F) activates β-glucanase, which breaks down gummy β-glucans in the mash, making the sugars flow out more freely later in the process. In the modern mashing process, commercial fungal based β-glucanase may be added as a supplement. Finally, a mash rest temperature of 65–71 °C (149–159.8 F) is used to convert the starches in the malt to sugar, which is then usable by the yeast later
in the brewing process. Doing the latter rest at the lower end of the range favors β-amylase enzymes, producing more low-order sugars like maltotriose

Maltotriose

Maltotriose is a trisaccharide consisting of three glucose molecules linked with α-1,4 glycosidic bonds.It is most commonly produced by the digestive enzyme alpha-amylase on amylose in starch...

, maltose

Maltose

Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....

, and glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 which are more fermentable by the yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

. This in turn creates a beer lower in body and higher in alcohol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. A rest closer to the higher end of the range favors α-amylase enzymes, creating more higher-order sugars and dextrin

Dextrin

Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....

s which are less fermentable by the yeast, so a fuller-bodied beer with less alcohol is the result. Duration and pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 variances also affect the sugar composition of the resulting wort.

Lautering

Lautering is the separation of the wort

Wort (brewing)

Wort, , is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars that will be fermented by the brewing yeast to produce alcohol.- Production :...

 (the liquid containing the sugar extracted during mashing) from the grains. This is done either in a mash tun outfitted with a false bottom, a lauter tun, or a mash filter. Most separation processes have two stages: first wort run-off, during which the extract is separated in an undiluted state from the spent grains, and sparging, in which extract which remains with the grains is rinsed off with hot water. The lauter tun is a tank with holes in the bottom small enough to hold back the large bits of grist and hulls. The bed of grist that settles on it is the actual filter. Some lauter tuns have provision for rotating rakes

Mash rake

A mash rake or mashing rake is a tool used in the mashing process of brewing and distilling. The mash rake churns the mash to ensure it is mixed properly and is wet everywhere, so no sugars are wasted....

 or knives to cut into the bed of grist to maintain good flow. The knives can be turned so they push the grain, a feature used to drive the spent grain out of the vessel. The mash filter is a plate-and-frame filter. The empty frames contain the mash, including the spent grains, and have a capacity of around one hectoliter. The plates contain a support structure for the filter cloth. The plates, frames, and filter cloths are arranged in a carrier frame like so: frame, cloth, plate, cloth, with plates at each end of the structure. Newer mash filters have bladders that can press the liquid out of the grains between spargings. The grain does not act like a filtration medium in a mash filter.

Boiling

Boiling the malt extracts, called wort, ensures its sterility, and thus prevents a lot of infections. During the boil hops are added, which contribute bitterness, flavour, and aroma compounds to the beer, and, along with the heat of the boil, causes proteins in the wort to coagulate and the pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 of the wort to fall. Finally, the vapours produced during the boil volatilise off flavours, including dimethyl sulfide

Dimethyl sulfide

Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...

 precursors.

The boil must be conducted so that it is even and intense. The boil lasts between 15 and 120 minutes, depending on its intensity, the hop addition schedule, and volume of water the brewer expects to evaporate.

Boiling equipment

The simplest boil kettles are direct-fired, with a burner underneath. These can produce a vigorous and favourable boil, but are also apt to scorch the wort where the flame touches the kettle, causing caramelisation and making clean up difficult.

Most breweries use a steam-fired kettle, which uses steam jackets in the kettle to boil the wort. The steam is delivered under pressure by an external boiler.

State-of-the-art breweries today use many interesting boiling methods, all of which achieve a more intense boiling and a more complete realisation of the goals of boiling.

Many breweries have a boiling unit outside of the kettle, sometimes called a calandria

Calandria

A calandria is the reactor core of the CANDU reactor. The calandria contains heavy water, a moderator used to moderate neutrons to achieve nuclear fission....

, through which wort is pumped. The unit is usually a tall, thin cylinder, with many tubes upwards through it. These tubes provide an enormous surface area on which vapor bubbles can nucleate, and thus provides for excellent volitisation. The total volume of wort is circulated seven to twelve times an hour through this external boiler, ensuring that the wort is evenly boiled by the end of the boil. The wort is then boiled in the kettle at atmospheric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

, and through careful control the inlets and outlets on the external boiler, an overpressure can be achieved in the external boiler, raising the boiling point by a few Celsius degrees. Upon return to the boil kettle, a vigorous vaporisation occurs. The higher temperature due to increased vaporization can reduce boil times up to 30%. External boilers were originally designed to improve performance of kettles which did not provide adequate boiling effect, but have
since been adopted by the industry as a sole means of boiling wort.

Modern brewhouses can also be equipped with internal calandria, which requires no pump. It works on basically the same principle as external units, but relies on convection to move wort through the boiler. This can prevent overboiling, as a deflector above the boiler reduces foaming, and also reduces evaporation. Internal calandria are generally difficult to clean.

Whirlpooling

At the end of the boil, the wort is set into a whirlpool. The so-called tea leaf paradox

Tea leaf paradox

The tea leaf paradox describes a phenomenon where tea leaves in a cup of tea migrate to the center and bottom of the cup after being stirred rather than being forced to the edges of the cup, as would be expected from a spiral centrifugal force...

 forces the denser solids (coagulated proteins, vegetable matter from hops) into a cone in the center of the whirlpool tank.

In most large breweries, there is a separate tank for whirl pooling. These tanks have a large diameter to encourage settling, and is flat bottomed or with a slope of 1 or 2° towards the outlet, a tangential inlet near the bottom of the whirlpool, and an outlet on the bottom near the outer edge of the whirlpool. A whirlpool should have no internal protrusions that might slow down the rotation of the liquid. The bottom of the whirlpool is often slightly sloped towards the outlet. Newer whirlpools often have "Denk rings" suspended in the middle of the whirlpool. These rings are aligned horizontally and have about 75% of the diameter of the whirlpool. The Deck rings prevent the formation of secondary eddies in the whirlpool, encouraging the formation of a cohesive trub cone in the middle of the whirlpool. Smaller breweries often use the brew kettle as a whirlpool. The trub being the solids that the brewer wants to remove from the wort.

Hopback

A hopback is a sealed chamber that is inserted in between the brewing kettle and counter-flow wort

Wort (brewing)

Wort, , is the liquid extracted from the mashing process during the brewing of beer or whisky. Wort contains the sugars that will be fermented by the brewing yeast to produce alcohol.- Production :...

 chiller. Hops

Hops

Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...

 are added to the chamber, the hot wort from the kettle is run through it, and then immediately cooled in the wort chiller before entering the fermentation chamber. It facilitates maximum retention of volatile hop aroma compounds that would normally be driven off when the hops contact the hot wort. Because it is a sealed chamber, the volatile hop compounds are trapped in the hot wort, and then the wort is immediately cooled, which keeps the volatile compounds in solution.

In the United Kingdom, it is common practice to use a hopback to clear the green wort (green wort is wort to which yeast has not yet been added). This device has the same effect as, but operates in a completely different manner than, a whirlpool. The two devices are often confused but are in function, quite different. While a whirlpool functions through the use of centrifugal forces, a hopback uses a layer of fresh hop flowers in a confined space to act as a filter bed to remove trub . Furthermore, while a whirlpool is only useful for the removal of pelleted hops (as flowers don't tend to separate as easily), hopbacks are generally used only for the removal of whole flower hops (as the particles left by pellets tend to make it through the hopback.)

Wort cooling

After the whirlpool, the wort must be brought down to fermentation temperatures (20–26°Celsius) before yeast is added. In modern breweries this is achieved through a plate heat exchanger

Heat exchanger

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

. A plate heat exchanger has many ridged plates, which form two separate paths. The wort is pumped into the heat exchanger, and goes through every other gap between the plates. The cooling medium, usually water, goes through the other gaps. The ridges in the plates ensure turbulent flow. A good heat exchanger can drop 95 °C wort to 20 °C while warming the cooling medium from about 10 °C to 80 °C. The last few plates often use a cooling medium which can be cooled to below the freezing point

Freezing Point

Freezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...

, which allows a finer control over the wort-out temperature, and also enables cooling to around 10 °C. After cooling, oxygen is often dissolved into the wort to revitalize the yeast and aid its reproduction.

While boiling, it is useful to recover some of the energy used to boil the wort. On its way out of the brewery, the steam created during the boil is passed over a coil through which unheated water flows. By adjusting the rate of flow, the output temperature of the water can be controlled. This is also often done using a plate heat exchanger. The water is then stored for later use in the next mash, in equipment cleaning, or wherever necessary.

Another common method of energy recovery takes place during the wort cooling. When cold water is used to cool the wort in a heat exchanger, the water is significantly warmed. In an efficient brewery, cold water is passed through the heat exchanger at a rate set to maximize the water's temperature upon exiting. This now-hot water is then stored in a hot water tank.

Fermenting

Fermentation

Fermentation (food)

Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...

 in brewing is the conversion of carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

s to alcohols and carbon dioxide or organic acids using yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

s, bacteria, or a combination thereof, under anaerobic

Anaerobic respiration

Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...

 conditions. A more restricted definition of fermentation is the chemical conversion of sugars into ethanol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. The science of fermentation is known as zymurgy.

After the wort is cooled and aerated – usually with sterile

Asepsis

Asepsis is the state of being free from disease-causing contaminants or, preventing contact with microorganisms. The term asepsis often refers to those practices used to promote or induce asepsis in an operative field in surgery or medicine to prevent infection...

 air – yeast is added to it, and it begins to ferment. It is during this stage that sugars won from the malt

Malt

Malt is germinated cereal grains that have been dried in a process known as "malting". The grains are made to germinate by soaking in water, and are then halted from germinating further by drying with hot air...

 are metabolized into alcohol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 and carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

, and the product can be called beer for the first time. Fermentation happens in tanks which come in all sorts of forms, from enormous cylindro-conical vessels, through open stone vessels, to wooden vats.

Most breweries today use cylindro-conical vessels, or CCVs, which have a conical bottom and a cylindrical top. The cone's aperture

Aperture

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

 is typically around 60°, an angle that will allow the yeast to flow towards the cone's apex, but is not so steep as to take up too much vertical space. CCVs can handle both fermenting and conditioning in the same tank. At the end of fermentation, the yeast and other solids which have fallen to the cone's apex can be simply flushed out of a port at the apex.

Open fermentation vessels are also used, often for show in brewpubs, and in Europe in wheat beer fermentation. These vessels have no tops, which makes harvesting top fermenting yeasts very easy. The open tops of the vessels make the risk of infection greater, but with proper cleaning procedures and careful protocol about who enters fermentation chambers, the risk can be well controlled.

Fermentation tanks are typically made of stainless steel. If they are simple cylindrical tanks with beveled ends, they are arranged vertically, as opposed to conditioning tanks which are usually laid out horizontally. Only a very few breweries still use wooden vats for fermentation as wood is difficult to keep clean and infection-free and must be repitched more or less yearly.

After high krausen

Krausen

Kräusen, also spelled "kraeusen" or "krausen", pronounced "KROY-zen", is a beer-brewing term that has two definitions in that context.1. A method to carbonate beer in which wort is added to the fermented/finished beer to carbonate.2...

 occurs, a bung

Bung

A bung is truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal...

 device (German: Spundapparat) is often put on the tanks to allow the C

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 O

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

2

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

produced by the yeast to naturally carbonate the beer. This bung device can be set to a given pressure to match the type of beer being produced. The more pressure the bung holds back, the more carbonated the beer becomes.

Fermentation methods

There are three main fermentation methods, warm, cool and wild or spontaneous. Fermentation may take place in open or closed vessels. There may be a secondary fermentation which can take place in the brewery, in the cask

Cask ale

Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer which is conditioned and served from a cask without additional nitrogen or carbon dioxide pressure...

 or in the bottle

Bottle conditioning

Bottle conditioned beers are either unfiltered so the final conditioning of the beer takes place in the bottle, or filtered and then reseeded with yeast so that an additional fermentation may take place.-Priming:...

.

Brewing yeasts may be classed as "top cropping" (or "top fermenting") and "bottom cropping" (or "bottom-fermenting"). This distinction was introduced by the Dane Emil Christian Hansen

Emil Christian Hansen

Emil Christian Hansen was a Danish mycologist and fermentation physiologist.Born in Ribe, he financed his education by writing novels and he was awarded a gold medal in 1876 for an essay on fungi....

. Top cropping yeasts are so called because they form a foam at the top of the wort

Wort

Wort may refer to:* Wort, the liquid created by the mashing of malted barley to use in brewing beer* Worting, Hampshire, a large district and suburb of the town of Basingstoke, in Hampshire, England....

 during fermentation. They can produce higher alcohol

Ethanol

Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

 concentrations and in higher temperatures, typically 16 to 24 °C (60.8 to 75.2 F), produce fruitier, sweeter beers. An example of a top cropping yeast is Saccharomyces cerevisiae

Saccharomyces cerevisiae

Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...

. Bottom cropping yeasts are typically used to produce cool fermented, lager

Lager

Lager is a type of beer made from malted barley that is brewed and stored at low temperatures. There are many types of lager; pale lager is the most widely-consumed and commercially available style of beer in the world; Pilsner, Bock, Dortmunder Export and Märzen are all styles of lager...

-type beers, though they can also ferment at higher temperatures if kept under 34C. These yeasts ferment more sugars, creating a dryer beer, and grow well at low temperatures. An example of bottom cropping yeast is Saccharomyces pastorianus

Saccharomyces pastorianus

Saccharomyces pastorianus is a yeast, used industrially for the production of lager beer. It is a synonym of the yeast species Saccharomyces carlsbergensis, which was originally described in 1883 by Emil Christian Hansen, who was working for the Danish brewery Carlsberg.-Genomics:As S...

, formerly known as Saccharomyces carlsbergensis.

For both types, yeast is fully distributed through the beer while it is fermenting, and both equally flocculate

Yeast flocculation

Yeast flocculation typically refers to the clumping together of brewing yeast once the sugar in a beer has been fermented into ethyl alcohol...

 (clump together and precipitate to the bottom of the vessel) when fermentation is finished. By no means do all top cropping yeasts demonstrate this behaviour, but it features strongly in many English yeasts which may also exhibit chain forming (the failure of budded cells to break from the mother cell) which is technically different from true flocculation.

The most common top cropping brewer's yeast, Saccharomyces cerevisiae, is the same species as the common baking yeast. However, baking and brewing yeasts typically belong to different strains, cultivated to favour different characteristics: baking yeast strains are more aggressive, in order to carbonate dough

Dough

Dough is a paste made out of any cereals or leguminous crops by mixing flour with a small amount of water and/or other liquid. This process is a precursor to making a wide variety of foodstuffs, particularly breads and bread-based items , flatbreads, noodles, pastry, and similar items)...

 in the shortest amount of time; brewing yeast strains act slower, but tend to produce fewer off-flavours and tolerate higher alcohol concentrations (with some strains, up to 22%).

To ensure purity of strain, a "clean" sample of brewing yeast is sometimes stored, either dried or refrigerated in a laboratory. After a certain number of fermentation cycles, a full scale propagation

Biological reproduction

Reproduction is the biological process by which new "offspring" individual organisms are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction...

 is produced from this laboratory sample. Typically, it is grown up in about three or four stages using sterile brewing wort and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

.

Warm fermenting

Yeasts such as Saccharomyces cerevisiae

Saccharomyces cerevisiae

Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...

are generally fermented at warm temperatures between 15–20 °C (59–68 F), occasionally as high as 24 °C (75.2 °F), while the yeast used by Brasserie Dupont for saison

Saison

Saison is the name originally given to low-alcohol pale ales brewed seasonally in farmhouses in Wallonia, the French-speaking region of Belgium, for farm workers during harvest season...

 ferments even higher at 29 °C (84 °F) to 35 °C (95 °F). They generally form a foam on the surface of the fermenting beer, as during the fermentation process its hydrophobic surface causes the flocs to adhere to CO₂ and rise; because of this they are often referred to as "top cropping" or "top fermenting" – though this distinction is less clear in modern brewing with the use of cylindro-conical tanks. Warm fermented beers are generally ready to drink within three weeks after the beginning of fermentation, although some brewers will condition them for several months.

Cool fermenting

Lager is beer that has been cool fermented at around 10 °C (50 °F), compared to typical warm fermentation temperatures of 18 °C (64.4 °F). It is then stored for 30 days or longer close to the freezing

Freezing

Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....

 point, and during this storage sulphur components developed during fermentation dissipate.

Though it is the cool fermenting that defines lager, the main technical difference with lager yeast is its ability to process raffinose

Raffinose

Raffinose is a trisaccharide composed of galactose, fructose, and glucose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase , an enzyme not found in the...

 (a trisaccharide composed of the sugars galactose

Galactose

Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....

, fructose

Fructose

Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...

, and glucose

Glucose

Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

) which means that all sugars are fermented, resulting in a well attentuated

Attenuation (brewing)

In brewing attenuation is the percentage that measures the conversion of sugars into alcohol and carbon dioxide by the fermentation process. The percentage is calculated by comparing weight or specific gravity of the extract before and after fermentation....

 beer; warm fermenting yeast only cleaves and ferments the fructose portion of raffinose, leaving melibiose

Melibiose

Melibiose is a reducing disaccharide formed by an alpha-1,6 linkage between galactose and glucose . It can be formed by invertase mediated hydrolysis of raffinose, which produces melibiose and fructose. Melibiose can be broken down into its component saccharides, glucose and galactose, by the...

, which it cannot further cleave into two monosaccharides due to its lack of melibiase, so ale remains sweeter with a lower conversion of sugar into alcohol. Raffinose is a minor dry component of Carlsberg barley, but once malted is practically nonexistent.

While the nature of yeast was not fully understood until Emil Hansen of the Carlsberg brewery in Denmark isolated a single yeast cell in the 1800s, brewers in Bavaria

Bavaria

Bavaria, formally the Free State of Bavaria is a state of Germany, located in the southeast of Germany. With an area of , it is the largest state by area, forming almost 20% of the total land area of Germany...

 had for centuries been selecting cold-fermenting lager yeasts by storing ("lagern") their beers in cold alpine caves. The process of natural selection meant that the wild yeasts that were most cold tolerant would be the ones that would remain actively fermenting in the beer that was stored in the caves. Some of these Bavarian yeasts were brought back to the Carlsberg brewery around the time that Hansen did his famous work.

Today, lagers represent the vast majority of beers produced. Examples include Budweiser Budvar, Birra Moretti

Birra Moretti

Birra Moretti was an Italian brewing company, founded in Udine in 1859 by Luigi Moretti. In 1996 the company was acquired by Heineken International. The brewing plant in Udine was sold to the newly formed Birra Castello S.p.A.; Moretti is now a brand of Heineken.- Brands :There are eight beers...

, Stella Artois

Stella Artois

Stella Artois is a 5% ABV lager brewed in Leuven, Belgium since 1926. In the UK, Canada and New Zealand a 4% ABV version is also available.-Production:...

, Red Stripe

Red Stripe

Red Stripe is a Jamaican lager beer whose logo is a bold, diagonal red stripe. It is brewed by Desnoes & Geddes Limited, originally a soft drink manufacturer incorporated on July 31, 1918, by Kingston, Jamaica natives Eugene Peter Desnoes and Thomas Hargreaves Geddes...

, and Singha

Singha

Singha, , is a 5% alcohol-by-volume pale lager produced by Boon Rawd Brewery. It is also available in 5% abv draught version as Singha Lager Draft, and the new 3.5% abv Singha Light introduced in 2006.- History :...

. Some lager-style beers market themselves as Pilsner which originated in Pilsen, Czech Republic (Plzeň in Czech

Czech language

Czech is a West Slavic language with about 12 million native speakers; it is the majority language in the Czech Republic and spoken by Czechs worldwide. The language was known as Bohemian in English until the late 19th century...

). However, Pilsners are brewed with 100% barley malt and aggressive hop bitterness, flavor, and aroma.

Lager yeast normally ferments at a temperature of approximately 5 °C (40 °Fahrenheit). Lager yeast can be fermented at a higher temperature normally used for top-fermenting yeast, and this application is often used in a beer style known as California Common or colloquially as "steam beer

Steam beer

Steam beer may be defined as a highly effervescent beer made by brewing lager yeasts at warm fermentation temperatures. It has two distinct but related meanings:*Historic steam beer produced in California from the mid-19th century to the mid-20th century;...

". Saccharomyces pastorianus

Saccharomyces pastorianus

Saccharomyces pastorianus is a yeast, used industrially for the production of lager beer. It is a synonym of the yeast species Saccharomyces carlsbergensis, which was originally described in 1883 by Emil Christian Hansen, who was working for the Danish brewery Carlsberg.-Genomics:As S...

is used in the brewing of lager

Lager

Lager is a type of beer made from malted barley that is brewed and stored at low temperatures. There are many types of lager; pale lager is the most widely-consumed and commercially available style of beer in the world; Pilsner, Bock, Dortmunder Export and Märzen are all styles of lager...

.

Spontaneous fermentation

These beers are primarily brewed around Brussels, Belgium. They are fermented in oak barrels after being inoculated with wild yeast and bacteria while cooling in a Koelship. Wild yeast and bacteria ferment the wort

Wort

Wort may refer to:* Wort, the liquid created by the mashing of malted barley to use in brewing beer* Worting, Hampshire, a large district and suburb of the town of Basingstoke, in Hampshire, England....

 in the oak barrels. The beers fermented from yeast and bacteria in the Brussels area are called Lambic

Lambic

Lambic is a very distinctive type of beer brewed only in the Pajottenland region of Belgium and in Brussels itself at the Cantillon Brewery and museum...

 beers. These bacteria add a sour flavour to the beer. Of the many styles of beer very few use bacteria, most are fermented with yeast alone and bacterial contamination is avoided.
However, with the advent of yeast banks and the National Collection of Yeast Cultures

National Collection of Yeast Cultures

The National Collection of Yeast Cultures is a yeast culture collection, established in 1951, and working under the Budapest Treaty for the storage of over 4,000 yeast cultures. Located at the Institute of Food Research in Norwich, England, since 1980. NCYC is part funded by the UK government but...

, brewing these beers – albeit not through spontaneous fermentation – is possible anywhere. Specific bacteria cultures are also available to reproduce certain styles.

Brettanomyces

Brettanomyces

Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of...

is a genus of yeast important in brewing lambic

Lambic

Lambic is a very distinctive type of beer brewed only in the Pajottenland region of Belgium and in Brussels itself at the Cantillon Brewery and museum...

, a beer produced not by the deliberate addition of brewer's yeasts, but by spontaneous fermentation with wild yeasts and bacteria.

Secondary fermentation

After initial or primary fermentation, the beer may be transferred into a second container, so that it is no longer exposed to the dead yeast and other debris (also known as "trub") that have settled to the bottom of the primary fermenter. This prevents the formation of unwanted flavours and harmful compounds such as acetylaldehydes, which are commonly blamed for hangovers. During secondary fermentation, most of the remaining yeast will settle to the bottom of the second fermenter, yielding a less hazy product.

Bottle fermentation

Some beers undergo a fermentation in the bottle, giving natural carbonation. This may be a second or third fermentation. They are bottled with a viable yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

 population in suspension. If there is no residual fermentable sugar left, sugar may be added. The resulting fermentation generates CO₂

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 which is trapped in the bottle, remaining in solution and providing natural carbonation.

Cask conditioning

Cask ale or cask-conditioned beer is the term for unfiltered

Filtration

Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...

 and unpasteurised

Pasteurization

Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...

 beer which is conditioned (including secondary fermentation) and served from a cask without additional nitrogen or carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

.

Conditioning

When the sugars in the fermenting beer have been almost completely digested, the fermentation slows down and the yeast starts to settle to the bottom of the tank. At this stage, the beer is cooled to around freezing, which encourages settling of the yeast, and causes proteins to coagulate and settle out with the yeast. If a separate conditioning tank is to be used, it is at this stage that the beer will be transferred into one. Unpleasant flavours such as phenolic compounds become insoluble in the cold beer, and the beer's flavour becomes smoother. During this time pressure is maintained on the tanks to prevent the beer from going flat.

Conditioning can take from 2 to 4 weeks, sometimes longer, depending on the type of beer. Additionally lagers, at this point, are aged at near freezing temperatures for 1–6 months depending on style. This
cold aging serves to reduce sulphur compounds produced by the bottom-fermenting yeast and to produce a cleaner tasting final product with fewer esters.

If the fermentation tanks have cooling jackets on them, as opposed to the whole fermentation cellar being cooled, conditioning can take place in the same tank as fermentation. Otherwise separate tanks (in a separate cellar) must be employed. This is where aging occurs.

Filtering

Filtering the beer stabilizes the flavour, and gives beer its polished shine and brilliance. Not all beer is filtered. When tax determination is required by local laws, it is typically done at this stage in a calibrated tank.

Filters come in many types. Many use pre-made filtration media such as sheets or candles, while others use a fine powder made of, for example, diatomaceous earth

Diatomaceous earth

Diatomaceous earth also known as diatomite or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 1 micrometre to more than 1 millimetre, but typically 10 to...

, also called kieselguhr, which is introduced into the beer and recirculated past screens to form a filtration bed.

Filters range from rough filters that remove much of the yeast and any solids (e.g. hops, grain particles) left in the beer, to filters tight enough to strain colour and body from the beer. Normally used filtration ratings are divided into rough, fine and sterile. Rough filtration leaves some cloudiness in the beer, but it is noticeably clearer than unfiltered beer. Fine filtration gives a glass of beer that you could read a newspaper through, with no noticeable cloudiness. Finally, as its name implies, sterile filtration is fine enough that almost all microorganisms in the beer are removed during the filtration process.

Sheet (pad) filters
These filters use pre-made media and are relatively straightforward. The sheets are manufactured to allow only particles smaller than a given size through, and the brewer is free to choose how finely to filter the beer. The sheets are placed into the filtering frame, sterilized (with hot water, for example) and then used to filter the beer. The sheets can be flushed if the filter becomes blocked, and usually the sheets are disposable and are replaced between filtration sessions. Often the sheets contain powdered filtration media to aid in filtration.

It should be kept in mind that pre-made filters have two sides. One with loose holes, and the other with tight holes. Flow goes from the side with loose holes to the side with the tight holes, with the intent that large particles get stuck in the large holes while leaving enough room around the particles and filter medium for smaller particles to go through and get stuck in tighter holes.

Sheets are sold in nominal ratings, and typically 90% of particles larger than the nominal rating are caught by the sheet.

Kieselguhr filters
Filters that use a powder medium are considerably more complicated to operate, but can filter much more beer before needing to be regenerated. Common media include diatomaceous earth

Diatomaceous earth

Diatomaceous earth also known as diatomite or kieselgur/kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that is easily crumbled into a fine white to off-white powder. It has a particle size ranging from less than 1 micrometre to more than 1 millimetre, but typically 10 to...

, or kieselguhr, and perlite

Perlite

Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently...

.

Packaging

Packaging is putting the beer into the containers in which it will leave the brewery. Typically this means putting the beer into bottles, aluminium cans and keg

Keg

A keg is a small barrel.Traditionally, a wooden keg is made by a cooper used to transport items such as nails, gunpowder., and a variety of liquids....

s, but it may include putting the beer into bulk tanks for high-volume customers.

Brewing methods

There are several additional brewing methods, such as barrel aging, double dropping, and Yorkshire Square.

By-products

Brewing by-products are "brewer's grains

Brewer's spent grain

Brewer's spent grain is a byproduct of beer brewing consisting of the residue of malt and grain which remains in the mash-kettle after the mashing and lautering process. It consists primarily of grain husks, pericarp, and fragments of endosperm...

" and dregs (typically dried and resold as "brewers dried yeast") from the filtration process. Brewer's grains are sold as fodder

Fodder

Fodder or animal feed is any agricultural foodstuff used specifically to feed domesticated livestock such as cattle, goats, sheep, horses, chickens and pigs. Most animal feed is from plants but some is of animal origin...

, and often used as an ingredient in compound feed

Compound feed

Compound feeds are feedstuffs that are blended from various raw materials and additives. These blends are formulated according to the specific requirements of the target animal...

. Yeast extract

Yeast extract

Yeast extract is the common name for various forms of processed yeast products made by extracting the cell contents ; they are used as food additives or flavourings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations. Monosodium...

 is obtained from an additional production process using brewers dried yeast.

External links

• An overview of the microbiology behind beer brewing from the Science Creative Quarterly
• Hyfoma on beer brewing – Hyfoma
• A pictorial overview of the brewing process at the Heriot-Watt University Pilot Brewery