Brewing
From Wikipedia, the free encyclopedia
- Brewing can also refer to steeping, as in the preparation of tea.
Brewing is the production of alcoholic beverages and alcohol fuel through fermentation. This is the method used in beer production, although the term can be used for other drinks such as sake, mead and wine. The term is also sometimes used to refer to any chemical mixing process.
Brewing has a very long history, and archeological evidence tells us that this technique was used in ancient Egypt. Descriptions of various beer recipes can be found in Sumerian writings, some of the oldest known writing of any sort.
The brewing industry is part of most western economies.
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[edit] Brewing beer
All beers are brewed using a process based on a simple formula. Key to the process is malted grain, depending on the region traditionally barley, wheat or sometimes rye. (When malting rye, due care must be taken to prevent ergot poisoning (ergotism), as rye is particularly prone to developing this toxic fungus during the malting process.)
Malt is made by allowing a grain to germinate, after which it is then dried in a kiln and sometimes roasted. The germination process creates a number of enzymes, notably α-amylase and β-amylase, which will be used to convert the starch in the grain into sugar. Depending on the amount of roasting, the malt will take on dark colour and strongly influence the colour and flavour of the beer.
The malt is crushed to break apart the grain kernels, increase their surface area, and separate the smaller pieces from the husks. The resulting grist is mixed with heated water in a vat called a "mash tun" for a process known as "mashing". During this process, natural enzymes within the malt break down much of the starch into sugars which play a vital part in the fermentation process. Mashing usually takes 1 to 2 hours, and during this time various temperature rests (waiting periods) activate different enzymes depending upon the type of malt being used, its modification level, and the desires of the brewmaster. The activity of these enzymes convert the starches of the grains to dextrines and then to fermentable sugars such as maltose. The Mash Tun generally contains a slotted "false bottom" or other form of manifold which acts as a strainer allowing for the separation of the liquid from the grain.
A mash rest from 120 °F to 130 °F (49 °C to 55 °C) activates various proteinases, which break down proteins that might otherwise cause the beer to be hazy. But care is of the essence since the head on beer is also composed primarily of proteins, so too aggressive a protein rest can result in a beer that cannot hold a head. 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 and rice, which are widely used in North American beers. A mash rest at 60°C or 140°F activates beta-glucanase, which breaks down gummy beta-glucans in the mash, making the sugars flow out more freely later in the process. In the modern mashing process commercial fungal based beta-glucanase may be added as a supplement. Finally, a mash rest temperature of 149 to 160 °F (65 to 71 °C) 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 produces more low-order sugars which are more fermentable by the yeast. This in turn creates a beer lower in body and higher in alcohol. A rest closer to the higher end of the range creates more higher-order sugars which are less fermentable by the yeast, so a fuller-bodied beer with less alcohol is the result.
After the mashing, the resulting liquid is strained from the grains in a process known as lautering. Prior to lautering, the mash temperature may be raised to 165 °F to 170 °F (about 75 °C) (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 (rhymes with hurt). The wort is moved into a large tank known as a "copper" or kettle where it is boiled with hops and sometimes other ingredients such as herbs or sugars. The boiling process serves to terminate enzymatic processes, precipitate proteins, isomerize hop resins, concentrate and sterilize the wort. Hops add flavour, aroma and bitterness to the beer. At the end of the boil, the hopped wort settles to clarify it in a vessel called a "whirl-pool" and the clarified wort is then cooled.
The wort is then moved into a "fermentation vessel" where yeast is added or "pitched" with it. The yeast converts the sugars from the malt into alcohol, carbon dioxide and other components through a process called Glycolysis. After a week to three weeks, the fresh (or "green") beer is run off into conditioning tanks. After conditioning for a week to several months, the beer is often filtered to remove yeast and particulates. The "bright beer" is then ready for serving or packaging.
There are four main families of beer styles determined by the variety of yeast used in their brewing.
[edit] Ale (top-fermenting yeasts)
Ale yeasts ferment at warmer temperatures between 15°C and 20°C (60°F to 68°F), and occasionally as high as 24°C (75°F). Pure ale yeasts form a foam on the surface of the fermenting beer, because of this they are often referred to as Top-Fermenting yeast - though there are some British ale yeast strains that settle at the bottom. Ales are generally ready to drink within three weeks after the beginning of fermentation, however, some styles benefit from additional aging for several months or years. Ales range in color from very pale to black opaque. England is best known for its variety of Ales.
[edit] Lager (bottom-fermenting yeasts)
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 had for centuries been selecting these cold-fermenting Lager yeasts by storing or "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 stolen and brought back to the Carlsberg brewery around the time that Hansen did his famous work.
Lager yeast tends to collect at the bottom of the fermenter and is often referred to as Bottom-Fermenting yeast. Lager is fermented at much lower temperatures, around 10°C (50°F), compared to typical ale fermentation temperatures of 18°C (65°F). It is then stored for 30 days or longer close to the freezing point. During the storing or Lagering process, the beer mellows and flavours become smoother. Sulfur components developed during fermentation dissipate. The popularity of lager was a major factor that led to the rapid introduction of refrigeration in the early 1900s.
Today, lagers represent the vast majority of beers produced, the most famous being a light lager called Pilsner which originated in Pilsen, Czech Republic (Plzeň in czech language). It is a common misconception that all Lagers are light in color: lagers can range from very light to deep black, just like Ales.
[edit] Beers of Spontaneous Fermentation (wild yeasts)
These beers are nowadays primarily only brewed around Brussels, Belgium. They are fermented by means of wild yeast strains that live in a part of the Zenne river which flows through Brussels. These beers are also called Lambic beers. However with the advent of yeast banks and the NCYC, brewing these beers, although not through spontaneous fermentation, is possible anywhere.
[edit] Beers of mixed origin
These beers are blends of spontaneous fermentation beers and ales or lagers or they are ales/lagers which are also fermented by wild yeasts.
[edit] The brewing process
Work in the brewery is typically divided into 7 steps: mashing, lautering, boiling, fermenting, conditioning, filtering, and filling.
[edit] Mashing
Mashing is the process of mixing milled grain (typically malted grain) with water, and heating this mixture up with rests at certain temperatures to allow enzymes in the malt to break down the starch in the grain into sugars, typically maltose.
[edit] Lautering
Lautering is the separation of the extracts won during mashing from the spent grain. It is achieved in either a Lauter tun, a wide vessel with a false bottom, or a mash filter, a plate-and-frame filter designed for this kind of separation. Lautering has 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.
[edit] Lauter tun
A Lauter Tun is the traditional vessel used for separation of the extracted wort. While the basic principle of its operation has remained the same since its first use, technological advances have led to better designed lauter tuns capable of quicker and more complete extraction of the sugars from the grain.
The false bottom in a lauter tun has thin (0.7 to 1.1 mm) slits to hold back the solids and allow liquids to pass through. The solids, not the false bottom, form a filtration medium and hold back small solids, allowing the otherwise cloudy mash to run out of the lauter tun as a clear liquid. The false bottom of a lauter tun is today made of wedge wire, which can provide a free-flow surface of up to 12% of the bottom of the tun.
The run off tubes should be evenly distributed across the bottom, with one tube servicing about 1 m² of area. Typically these tubes have a wide, shallow cone around them to prevent drastic forces from compacting the grain directly above the outlet. In the past the run-off tubes flowed through swan-neck valves into a wort collection grant. While visually stunning, this system led to a lot of oxygen uptake. Such a system has mostly been replaced either by a central wort-collection vessel or the arrangement of outlet ports into concentric zones, with each zone having a ring-shaped collection pipe. Brewhouses in plain public view, particularly those in brewpubs, often maintain the swan-neck valves and grant for their visual effect.
A quality lauter tun has rotating rake arms with a central drive unit. Depending on the size of the lauter tun, there can be between two and six rake arms. Cutting blades hang from these arms. The blade is usually wavy and has a plough-like foot. Each blade has its own path around the tun and the whole rake assembly can be raised and lowered. Attached to each of these arms is a flap which can be raised and lowered for pushing the spent grains out of the tun. The brewer, or better yet an automated system, can raise and lower the rake arms depending on the turbidity (cloudiness) of the run-off, and the tightness of the grain bed, as measured by the pressure difference between the top and bottom of the grain bed.
There must be a system for introducing sparge water into the lauter tun. Most systems have a ring of spray heads that insure an even and gentle introduction of the sparge water. The watering system should not beat down on the grain bed and form a channel.
Large breweries have self-closing inlets on the bottom of the tun through which the mash is transferred to the lauter tun, and one outlet, also on the bottom of the tun, into which the spent grains fall after lautering is complete. Craft breweries often have manways on the side of the mash tun for spent grain removal, which then must be helped along to a large extent by the brewer.
Some small breweries use a combination mash/lauter tun, in which the rake system cannot be implemented because the mixing mechanism for mashing is of higher importance. The stirring blades can be used as an ersatz rake, but typically they cannot be moved up and down, and would disturb the bed too much were they used deep in the grain bed.
[edit] Mash filter
A 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.
[edit] Boiling
Boiling the won extracts, called wort, ensures its sterility, and thus prevents a lot of infections. During the boil hops are added, which contribute bitterness, flavor, and aroma compounds to the beer, and, along with the heat of the boil, causes proteins in the wort to coagulate and the pH of the wort to fall. Finally, the vapors produced during the boil volatilize off flavors, including dimethyl sulfide precursors.
The boil must be conducted so that is it even and intense. The boil lasts between 50 and 120 minutes, depending on its intensity, the hop addition schedule, and volume of wort the brewer expects to evaporate.
[edit] Boiling equipment
The simplest boil kettles are direct-fired, with a burner underneath. These can produce a vigorous and favorable boil, but are also apt to scorch the wort where the flame touches the kettle, causing caramelization 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 realization of the goals of boiling.
Many breweries have a boiling unit outside of the kettle, sometimes called a calandria, 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 volitization. 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, and through careful control the inlets and outlets on the external boiler, an overpressure can be achieve in the external boiler, raising the boiling point a few Celsius degrees. Upon return to the boil kettle, a vigorous vaporization 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.
[edit] Energy recovery
Boiling wort takes a lot of energy, and it is wasteful to let this energy escape into the atmosphere. The simplest was to recover this energy is with a kettle vapor condenser (German: Pfaduko, from the much longer Pfannendunstkondensator). A kettle vapor condenser is often nothing more than a plate heat exchanger.
[edit] Whirlpool
At the end of the boil, the wort is set into a whirlpool. The so-called teacup effect forces the more dense 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 whirlpooling. These tanks have a large diameter to encourage settling, a flat bottom, 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 Denk 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 brewkettle as a whirlpool.
[edit] Wort cooling
After the whirlpool, the wort must be brought down to fermentation temperatures before yeast is added. In modern breweries this is achieved through a plate heat exchanger. 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, 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.
[edit] Fermenting
Fermentation, as a step in the brewing process, starts as soon as yeast is added to the cooled wort. This is also the point at which the product is first called beer. It is during this stage that sugars won from the malt are metabolized into alcohol and carbon dioxide. Fermentation tanks come in all sorts of forms, from enormous tanks which can look like storage silos, to five gallon glass carboys in a homebrewer's closet.
Most breweries today use cylindroconical vessels, or CCVs, have a conical bottom and a cylindrical top. The cone's aperture is typically around 60°, an angle that will allow the yeast to flow towards the cones 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 cones apex can be simply flushed out 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 when, 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 kraeusen a bung device (German: Spundapparat) is often put on the tanks to allow the CO2 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.
[edit] 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. Unpleasant flavors such as phenolic compounds become insoluble in the cold beer, and the beer's flavor becomes smoother. During this time pressure is maintained on the tanks to prevent the beer from going flat.
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.
[edit] Filtering
Filtering the beer stabilizes the flavor, 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, 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 color 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.
[edit] 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.
[edit] 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, or kieselguhr, and perlite.
[edit] Packaging
Packaging is putting the beer into the containers in which it will leave the brewery. Typically this means in bottles and kegs, but it might include bulk tanks for high-volume customers.
[edit] Secondary fermentation
Secondary fermentation is an additional fermentation after the first or primary fermentation. Some beers may have three fermentations.
Bottle fermentation
- See Bottle conditioning.
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 population in suspension. If there is no residual fermentable sugar left, sugar may be added. The resulting fermentation generates CO2 which is trapped in the bottle, remaining in solution and providing natural carbonation.
Cask conditioning
- See Cask ale.
Beer in casks are managed carefully to allow some of the carbonation to escape.
[edit] See also
- distilling.
- The word zymurgy is sometimes used as a generic term for brewing, winemaking and distilling.
- Brewery#The Brewing Process
- Homebrew
- History of beer
- Mead, honey mead and meadmaking
[edit] External links
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Wikimedia Commons has media related to: |
- How To Brew The definitive book on making quality beers at home. (Free of charge.)
- Beer Brewing Tips
- Brewery History Society founded in 1972 to promote research into all aspects of the brewing industry, to encourage the interchange of information about breweries and brewing, and to collect photographic and other archive information about brewery history.
- The River Wey and Wey Navigations Community Site — a non-commercial site of over 200,000 words all about the Wey Valley including information about the history of Brewing in southern England
- The British Library - finding information about the brewing industry
- Webpage with interactive Flowsheets on beer brewing
- An overview of the microbiology behind beer brewing from the Science Creative Quarterly
- Brewing news page - Alcohol and Drugs History Society
- Carling Brewing Process
