Editing Brewing

{{short description|Process in beer production}}
{{About|the brewing of beer|other uses|Brewing (disambiguation)}}
{{Redirect|Brewer}}{{About|2=the chemical details on the conversion of sugars into ethanol by fermentation|3=Ethanol fermentation}}{{See also|Brewing methods|Homebrewing}}
{{pp|small=yes}}

{{Use dmy dates|date=June 2020}}

[[File:The Brewer designed and engraved in the Sixteenth. Century by J Amman.png|right|thumb|A 16th-century brewery]]

'''Brewing''' is the production of [[beer]] by [[steeping]] a [[starch]] source (commonly [[cereal]] grains, the most popular of which is [[barley]])<ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA236|page=236|author=Evan Evans|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20191223055227/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA236|archive-date=23 December 2019|url-status=live}}</ref> in water and [[#Fermenting|fermenting]] the resulting sweet liquid with [[Yeast#Beer|yeast]].  It may be done in a [[brewery]] by a commercial brewer, at home by a [[homebrewer]], or communally.<ref>{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA111|title=Encyclopaedia of Brewing|page=111|author=Chris Boulton|publisher=John Wiley & Sons|date=20 May 2013|isbn=9781118598122|archive-url=https://web.archive.org/web/20160521101002/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA111|archive-date=21 May 2016|url-status=live}}</ref> Brewing has taken place since around the 6th millennium BC, and archaeological evidence suggests that emerging civilizations, including [[ancient Egypt]],<ref name="Arnold" /> [[China]],<ref name=China/> and [[Mesopotamia]], brewed beer.<ref name="Hartman">{{cite journal|author1=Louis F Hartman  |author2=A. L. Oppenheim |name-list-style=amp |date=December 1950 |title=On Beer and Brewing Techniques in Ancient Mesopotamia |journal=Journal of the American Oriental Society |volume=10|issue=Supplement }}</ref> Since the nineteenth century the [[#brewing industry|brewing industry]] has been part of most western economies.

The basic ingredients of beer are water and a [[Fermentation|fermentable]] starch source such as [[malted barley]]. Most beer is fermented with a [[brewer's yeast]] and flavoured with [[hops]].<ref name="alabev.com"/> Less widely used starch sources include [[millet]], [[sorghum]] and [[cassava]].<ref name="BeerHunter.com"/> Secondary sources ([[adjuncts]]), such as maize (corn), rice, or sugar, may also be used, sometimes to reduce cost, or to add a feature, such as adding wheat to aid in retaining the foamy head of the beer.<ref name="beer-brewing.com"/> The most common starch source is ground cereal or "grist" – the proportion of the starch or cereal ingredients in a beer recipe may be called grist, grain bill, or simply [[mash ingredients]].<ref name="grist" />

Steps in the brewing process include [[malting]], [[Mill (grinding)|milling]], [[#Mashing|mashing]], [[#Lautering|lautering]], [[#Boiling|boiling]], [[#Fermenting|fermenting]], [[#Conditioning|conditioning]], [[#Filtering|filtering]], and [[#Packaging|packaging]]. There are three main fermentation methods: [[#Warm fermenting|warm]], [[#Cool fermenting|cool]] and [[#Spontaneous fermentation|spontaneous]]. Fermentation may take place in an open or closed fermenting vessel; a secondary fermentation may also occur in the [[#Cask conditioning|cask]] or [[#Bottle conditioning|bottle]]. There are several additional [[brewing methods]], such as [[Brewing methods#Burtonisation|Burtonisation]], [[Brewing methods#Double dropping|double dropping]], and [[Brewing methods#Yorkshire Square|Yorkshire Square]], as well as post-fermentation treatment such as [[#Filtering|filtering]], and [[Barrel-aged beer|barrel-ageing]].

==History==
{{Further|History of beer|Women in brewing}}
[[File:Alulu Beer Receipt.jpg|left|thumb|The Alulu beer receipt records a purchase of  "best" beer from a brewer, {{Circa|2050 BC}}, from the [[Sumer]]ian city of [[Umma]] in [[Mesopotamia]] (ancient Iraq).<ref>{{Cite web |url=http://www.thefreelibrary.com/World%27s+oldest+beer+receipt%3F-a0141346971 |title=World's oldest beer receipt? – Free Online Library |publisher=thefreelibrary.com |access-date=8 May 2010 |archive-url=https://web.archive.org/web/20110511170952/http://www.thefreelibrary.com/World%27s+oldest+beer+receipt%3F-a0141346971 |archive-date=11 May 2011 |url-status=live }}</ref>]]{{See also|Fermentation in food processing#Brewing and winemaking}}
Brewing has taken place since around the 6th millennium BC, and archaeological evidence suggests emerging civilizations including [[China]],<ref name=China>{{cite journal|title=Fermented beverages of pre- and proto-historic China|author=Patrick E. McGovern|journal=Proceedings of the National Academy of Sciences |date=December 8, 2004|volume=101 |issue=51 |pages=17593–17598 |publisher=[[PNAS]]|doi=10.1073/pnas.0407921102 |pmid=15590771 |pmc=539767 |bibcode=2004PNAS..10117593M |doi-access=free }}</ref> [[ancient Egypt]], and [[Mesopotamia]] brewed beer. Descriptions of various beer recipes can be found in [[cuneiform]] (the oldest known writing) from ancient [[Mesopotamia]].<ref name="Arnold">{{Cite book|author=John P. Arnold |year=2005 |orig-year=1911 |title=Origin and History of Beer and Brewing: From Prehistoric Times to the Beginning of Brewing Science and Technology |publisher=BeerBooks |location=Cleveland, Ohio |page=34 |isbn=978-0-9662084-1-2 |oclc=71834130}}</ref><ref>{{Cite book |author=Max Nelson |title=The barbarian's beverage: a history of beer in ancient Europe |publisher=[[Routledge]] |location=London |year=2005 |url=https://www.amazon.co.uk/gp/reader/0415311217?p=S00H&checkSum=ha%2FMenougrV%2FCPWZg6P4td6OJoeMeVfRptT8FuSLUrk%3D |page=6 |isbn=978-0-415-31121-2 |oclc=58387214 |access-date=30 August 2017 |archive-url=https://web.archive.org/web/20071205213808/http://www.amazon.co.uk/gp/reader/0415311217?p=S00H&checkSum=ha%2FMenougrV%2FCPWZg6P4td6OJoeMeVfRptT8FuSLUrk%3D |archive-date=5 December 2007 |url-status=live }}</ref><ref>{{cite encyclopedia|url=https://www.britannica.com/eb/article-66615/beer|title=Beer - Alcoholic Beverage|author=Thomas W. Young|encyclopedia=Britannica.com|access-date=14 February 2010|archive-url=https://web.archive.org/web/20070511010251/https://www.britannica.com/eb/article-66615/beer|archive-date=11 May 2007|url-status=live}}</ref> In Mesopotamia the brewer's craft was the only profession which derived social sanction and divine protection from female deities/goddesses, specifically: [[Ninkasi]], who covered the production of beer, [[Siris (goddess)|Siris]], who was used in a metonymic way to refer to beer, and [[Siduri]], who covered the enjoyment of beer.<ref name="Hartman" /> In pre-industrial times, and in developing countries, women are frequently the main brewers.<ref>{{cite book|author=Christine Eber|title=Women and Alcohol in a Highland Maya Town: Water of Hope, Water of Sorrow|url=https://archive.org/details/womenalcoholinhi0009eber|url-access=registration|edition=revised|year=2000|publisher=University of Texas Press|location=Austin, Texas|isbn=978-0-292-72104-3|page=[https://archive.org/details/womenalcoholinhi0009eber/page/7 7]|access-date=20 November 2016}}</ref><ref>{{cite journal|author=Ray Anderson|title=The Transformation of Brewing: An Overview of Three Centuries of Science and Practice|journal=Brewery History|date=2005|volume=121|pages=5–24|url=http://www.breweryhistory.com/journal/archive/121/bh-121-005.htm |publisher=Brewery History Society |access-date=16 November 2016 |archive-url=https://web.archive.org/web/20161116171741/http://www.breweryhistory.com/journal/archive/121/bh-121-005.htm|archive-date=16 November 2016|url-status=live}}</ref>

As almost any cereal containing certain sugars can undergo [[#Spontaneous fermentation|spontaneous fermentation]] due to wild yeasts in the air, it is possible that beer-like beverages were independently developed throughout the world soon after a tribe or culture had domesticated cereal. Chemical tests of ancient pottery jars reveal that beer was produced as far back as about 7,000 years ago in what is today Iran. This discovery reveals one of the earliest known uses of fermentation and is the earliest evidence of brewing to date. In Mesopotamia, the oldest evidence of beer is believed to be a 6,000-year-old Sumerian tablet depicting people drinking a beverage through reed straws from a [[communal bowl]]. A 3900-year-old Sumerian poem honouring Ninkasi, the patron goddess of brewing, contains the oldest surviving beer recipe, describing the production of [[beer]] from barley via bread. The invention of bread and beer has been argued to be responsible for humanity's ability to develop technology and build civilization.<ref>{{Cite journal|url=http://www.sciam.com/article.cfm?chanID=sa006&articleID=E699E9C7-E7F2-99DF-38A7329520CF67D6&colID=15|journal=[[Scientific American]]|volume=296|issue=5|pages=102|date=May 2007|title=Ale's Well with the World|author=Steve Mirsky|access-date=4 November 2007|archive-url=https://web.archive.org/web/20071016205228/http://www.sciam.com/article.cfm?chanID=sa006&articleID=E699E9C7-E7F2-99DF-38A7329520CF67D6&colID=15|archive-date=16 October 2007|url-status=dead|bibcode=2007SciAm.296e.102M|doi=10.1038/scientificamerican0507-102|url-access=subscription}}</ref><ref>{{Cite news|author=Horst Dornbusch|url=http://www.aina.org/ata/20060827151956.htm|title=Beer: The Midwife of Civilization|publisher=Assyrian International News Agency|date=27 August 2006|access-date=4 November 2007|archive-url=https://web.archive.org/web/20100327184922/http://www.aina.org/ata/20060827151956.htm|archive-date=27 March 2010|url-status=live}}</ref><ref>{{cite web|url=http://www.beer-pages.com/stories/complete-guide-beer.htm|author=Roger Protz|title=The Complete Guide to World Beer|year=2004|quote=When people of the ancient world realised they could make bread and beer from grain, they stopped roaming and settled down to cultivate cereals in recognisable communities.|author-link=Roger Protz|access-date=18 December 2015|archive-url=https://web.archive.org/web/20110425062158/http://www.beer-pages.com/stories/complete-guide-beer.htm|archive-date=25 April 2011|url-status=live}}</ref> The earliest chemically confirmed barley beer to date was discovered at [[Godin Tepe]] in the central [[Zagros Mountains]] of Iran, where fragments of a jug, at least 5,000 years old was found to be coated with [[beerstone]], a by-product of the brewing process.<ref>{{cite web|url=http://www.penn.museum/sites/biomoleculararchaeology/?page_id=84|title=Barley Beer|publisher=[[University of Pennsylvania Museum of Archaeology and Anthropology]]|access-date=21 June 2011|archive-url=https://web.archive.org/web/20111008123537/http://www.penn.museum/sites/biomoleculararchaeology/?page_id=84|archive-date=8 October 2011|url-status=live}}</ref> Beer may have been known in [[Neolithic Europe]] as far back as 5,000 years ago,<ref>[http://www.stonepages.com/news/archives/000123.html] {{Webarchive|url=https://web.archive.org/web/20170712080128/http://www.stonepages.com/news/archives/000123.html|date=12 July 2017}} ''Prehistoric brewing: the true story'', 22 October 2001, Archaeo News. Retrieved 13 September 2008</ref> and was mainly brewed on a domestic scale.<ref>[http://www.dreherrt.hu/portal/main.php?heading_id=27&article_id=&language=en] {{Webarchive|url=https://web.archive.org/web/20090709015742/http://www.dreherrt.hu/portal/main.php?heading_id=27&article_id=&language=en|date=9 July 2009}} Dreher Breweries, ''Beer-history''</ref>

Ale produced before the [[Industrial Revolution]] continued to be made and sold on a domestic scale, although by the 7th century AD beer was also being produced and sold by European [[monasteries]]. During the Industrial Revolution, the production of beer moved from [[artisan]]al manufacture to [[Manufacturing|industrial manufacture]], and domestic manufacture ceased to be significant by the end of the 19th century.<ref name="Cornell 2003">{{Cite book|author=Martyn Cornell|title=Beer: The Story of the Pint|pages=47–49|year=2003|isbn=978-0-7553-1165-1|publisher=Headline}}</ref> The development of [[hydrometer]]s and [[thermometer]]s changed brewing by allowing the brewer more control of the process, and greater knowledge of the results. Today, the brewing industry is a global business, consisting of several dominant [[Multinational corporation|multinational companies]] and many thousands of smaller producers ranging from [[brewpub]]s to [[regional brewery|regional breweries]].<ref name="market"/> More than 133&nbsp;billion litres (35&nbsp;billion gallons) are sold per year—producing total global revenues of $294.5&nbsp;billion (£147.7&nbsp;billion) in 2006.<ref>{{cite web|url=http://www.researchandmarkets.com/reports/53577/beer_global_industry_guide.htm|title=Beer: Global Industry Guide|publisher=Research and Markets|access-date=5 November 2007|archive-url=https://web.archive.org/web/20071011084307/http://researchandmarkets.com/reports/53577/beer_global_industry_guide.htm|archive-date=11 October 2007|url-status=live}}</ref>

==Ingredients==
[[File:Sjb whiskey malt.jpg|right|thumb|[[Malting|Malted]] barley before kilning or roasting]]

The basic ingredients of beer are water; a starch source, such as [[malt]]ed [[barley]], able to be fermented (converted into alcohol); a [[brewer's yeast]] to produce the fermentation; and a flavouring, such as [[hops]],<ref name="alabev.com">[http://www.alabev.com/ingredie.htm alabev.com] {{webarchive|url=https://web.archive.org/web/20160123045417/http://www.alabev.com/ingredie.htm |date=23 January 2016 }} ''The Ingredients of Beer''. Retrieved 29 September 2008</ref> to offset the sweetness of the malt.<ref>{{cite book |url=https://books.google.com/books?id=ZjSKh24ZN9kC&pg=PA51 |title=Homebrewing For Dummies |page=51 |author=Marty Nachel |publisher=John Wiley & Sons |date=31 March 2008 |isbn=9781118052440 |access-date=18 April 2012 |archive-url=https://web.archive.org/web/20160504194419/https://books.google.com/books?id=ZjSKh24ZN9kC&pg=PA51 |archive-date=4 May 2016 |url-status=live }}</ref> A mixture of starch sources may be used, with a secondary saccharide, such as maize (corn), rice, or sugar, these often being termed [[adjuncts]], especially when used as a lower-cost substitute for malted barley.<ref name="beer-brewing.com">[http://www.beer-brewing.com/apex/beer_chapters/ch06_beer_adjuncts.htm beer-brewing.com] {{webarchive|url=https://web.archive.org/web/20071027063059/http://www.beer-brewing.com/apex/beer_chapters/ch06_beer_adjuncts.htm |date=27 October 2007 }} Ted Goldammer, ''The Brewers Handbook'', Chapter 6 – Beer Adjuncts, Apex Pub (1 January 2000), {{ISBN|0-9675212-0-3}}. Retrieved 29 September 2008</ref> Less widely used starch sources include [[millet]], [[sorghum]], and [[cassava]] root in Africa, potato in Brazil, and [[agave]] in Mexico, among others.<ref name="BeerHunter.com">{{cite web |url=http://www.beerhunter.com/documents/19133-000120.html |work=BeerHunter.com |author=Michael Jackson |title=A good beer is a thorny problem down Mexico way |date=1 October 1997 |access-date=29 September 2008 |archive-url=https://web.archive.org/web/20101204115213/http://www.beerhunter.com/documents/19133-000120.html |archive-date=4 December 2010 |url-status=live}}</ref> The most common starch source is ground cereal or "grist" – the proportion of the starch or cereal ingredients in a beer recipe may be called grist, grain bill, or simply [[mash ingredients]].<ref name="grist">{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA408|page=408|author=Paul Buttrick|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=9 September 2011|isbn=9780199912100|archive-url=https://web.archive.org/web/20191226172242/https://books.google.co.uk/books?id=Ga4MYyZq-RMC&pg=PA408|archive-date=26 December 2019|url-status=live}}</ref>

;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.<ref name="geot"/><ref>{{cite web |url=http://brewconductor.com/brewing/ingredients/water-for-brewing/ |title=Water For Brewing |access-date=18 June 2016 |archive-url=https://web.archive.org/web/20160817203048/http://brewconductor.com/brewing/ingredients/water-for-brewing/ |archive-date=17 August 2016 |url-status=live }}</ref> For example, [[Dublin]] has [[hard water]] well suited to making [[stout]], such as [[Guinness]]; while [[Plzeň|Pilsen]] has soft water well suited to making [[pale lager]], such as [[Pilsner Urquell]].<ref name="geot">{{Cite news|url=http://www.agiweb.org/geotimes/aug04/resources.html|title=Geology and Beer|work=Geotimes|date=August 2004|access-date=5 November 2007|archive-url=https://web.archive.org/web/20070927200414/http://www.agiweb.org/geotimes/aug04/resources.html|archive-date=27 September 2007|url-status=live}}</ref> The waters of [[Beer in England#Burton upon Trent|Burton]] in England contain [[gypsum]], which benefits making [[pale ale]] to such a degree that brewers of pale ales will add gypsum to the local water in a process known as [[Burtonisation]].<ref>[http://www.beerhunter.com/documents/19133-000098.html] {{Webarchive|url=https://web.archive.org/web/20100619014900/http://www.beerhunter.com/documents/19133-000098.html|date=19 June 2010}} Michael Jackson, BeerHunter, 19 October 1991, ''Brewing a good glass of water''. Retrieved 13 September 2008</ref>

;Starch source
{{Main|Malt|Mash ingredients}}
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]], and then drying the partially germinated grain in a kiln. Malting grain produces enzymes that will allow conversion from starches in the grain into fermentable sugars during the mash process.<ref>[[s:en:1911 Encyclopædia Britannica/Brewing/Chemistry|Wikisource]] 1911 Encyclopædia Britannica/Brewing/Chemistry. Retrieved 29 September 2008</ref> Different roasting times and temperatures are used to produce different colours of malt from the same grain. Darker malts will produce darker beers.<ref>[http://www.farm-direct.co.uk/farming/stockcrop/barley/malt.html Farm-direct] {{Webarchive|url=https://web.archive.org/web/20090814221734/http://www.farm-direct.co.uk/farming/stockcrop/barley/malt.html |date=14 August 2009 }} Oz, ''Barley Malt'', 6 February 2002. Retrieved 29 September 2008</ref>

Nearly all beer includes barley malt as the majority of the starch. This is because of its fibrous husk, which is important not only in the sparging stage of brewing (in which water is washed over the [[Mashing|mashed]] barley grains to form the [[wort]]) but also as a rich source of [[amylase]], a [[digestion|digestive]] [[enzyme]] that facilitates conversion of starch into sugars. Other malted and unmalted grains (including wheat, rice, oats, and [[rye]], and, less frequently, maize (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]]-containing grains like wheat, barley, and rye.<ref>{{cite web |author=Carolyn Smagalski |year=2006 |url=http://www.bellaonline.com/articles/art39558.asp |title=CAMRA & The First International Gluten Free Beer Festival |publisher=Carolyn Smagalski, Bella Online |access-date=14 July 2009 |archive-url=https://web.archive.org/web/20101002170600/http://www.bellaonline.com/articles/art39558.asp |archive-date=2 October 2010 |url-status=live}}</ref>

;Hops
{{Main|Hops}}
[[File:Humulus Lupulus Hopfendolde-mit-hopfengarten.jpg|thumb|left|[[Hops|Hop cone]] grown in a hop field, [[Hallertau]], Germany]]

Hops are the female flower clusters or seed cones of the hop vine ''[[Humulus lupulus]]'',<ref>{{cite web |url=http://www.lib.umn.edu/botanical/plant.php |title=University of Minnesota Libraries: The Transfer of Knowledge. Hops-''Humulus lupulus'' |publisher=Lib.umn.edu |date=13 May 2008 |access-date=20 May 2012 |archive-url=https://web.archive.org/web/20120305173530/http://www.lib.umn.edu/botanical/plant.php |archive-date=5 March 2012 |url-status=live }}</ref> which are used as a flavouring and preservative agent in nearly all beer made today.<ref>{{cite book |url=https://books.google.com/books?id=ojc4Uker_V0C&pg=PA45 |title=Encyclopedia of Jewish Food |author=Gil Marks |year=2012 |publisher=Wiley |isbn=9780470943540 |access-date=31 July 2012 |archive-url=https://web.archive.org/web/20160528211653/https://books.google.com/books?id=ojc4Uker_V0C&pg=PA45&lpg=PA45 |archive-date=28 May 2016 |url-status=live }}</ref> Hops had been used for medicinal and food flavouring purposes since Roman times; by the 7th century in [[Carolingian dynasty|Carolingian]] monasteries in what is now Germany, beer was being made with hops,<ref>{{cite book |url=https://books.google.com/books?id=7eYLjJp0y7UC&pg=PA54 |title=Beer in the Middle Ages and the Renaissance |page=54 |author=Richard W. Unger |publisher=University of Pennsylvania Press |year=2007 |isbn=978-0812203745 |access-date=1 August 2012 |archive-url=https://web.archive.org/web/20160522092458/https://books.google.com/books?id=7eYLjJp0y7UC&pg=PA54 |archive-date=22 May 2016 |url-status=live }}</ref> though it isn't until the thirteenth century that widespread cultivation of hops for use in beer is recorded.<ref name="Cornell 2003 62">{{Cite book|author=Martyn Cornell|title=Beer: The Story of the Pint|page=62|year=2003|isbn=978-0-7553-1165-1|publisher=Headline}}</ref> Before the thirteenth century, beer was flavoured with plants such as [[Achillea millefolium|yarrow]], [[Rhododendron tomentosum|wild rosemary]], and [[Myrica gale|bog myrtle]], and other ingredients such as [[Juniper berry|juniper berries]], [[aniseed]] and [[ginger]], which would be combined into a mixture known as [[gruit]] and used as hops are now used; between the thirteenth and the sixteenth century, during which hops took over as the dominant flavouring, beer flavoured with gruit was known as ale, while beer flavoured with hops was known as beer.<ref>{{cite book |url=https://books.google.com/books?id=QqnvNsgas20C&pg=PA534 |title=A History of Beer and Brewing |pages=534–535 |author=Ian S Hornsey |publisher=Royal Society of Chemistry |date=22 December 2003 |isbn=9780854046300 |access-date=1 August 2012 |archive-url=https://web.archive.org/web/20160506012014/https://books.google.com/books?id=QqnvNsgas20C&pg=PA534 |archive-date=6 May 2016 |url-status=live }}</ref><ref name="Ellix Pollan 2012">{{cite book|url=https://books.google.com/books?id=-zmLa205d0QC&pg=PA274|title=The Art of Fermentation|page=274|author1=Sandor Ellix Katz|author2=Michael Pollan|publisher=Chelsea Green Publishing|date=14 May 2012 |isbn=9781603583640 |access-date=1 August 2012|archive-url=https://web.archive.org/web/20160518220122/https://books.google.com/books?id=-zmLa205d0QC&pg=PA274|archive-date=18 May 2016|url-status=live}}</ref> Some beers today, such as ''Fraoch'' by the Scottish [[Williams Bros Brewing Co|Heather Ales company]] and ''Cervoise Lancelot'' by the French Brasserie-Lancelot company, use plants other than hops for flavouring.<ref>{{cite web|url=http://www.fraoch.com/historicales.htm |title=Heatherale.co.uk |publisher=Fraoch.com |access-date=28 September 2008 |archive-url=https://web.archive.org/web/20080629071231/http://www.fraoch.com/historicales.htm <!-- Bot retrieved archive --> |archive-date=29 June 2008}}</ref><ref>{{cite web |url=http://www.brasserie-lancelot.com/brasserie-lancelot.php |title=La Brasserie Lancelot est située au coeur de la Bretagne, dans des bâtiments rénovés de l'ancienne mine d'Or du Roc St-André, construits au XIX{{sup|e}} siècle sur des vestiges néolithiques |publisher=Brasserie-lancelot.com |access-date=28 September 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080819030220/http://www.brasserie-lancelot.com/brasserie-lancelot.php |archive-date=19 August 2008}}</ref>

Hops contain several characteristics that brewers desire in beer: they contribute a bitterness that balances the sweetness of the malt; they provide floral, citrus, and herbal aromas and flavours; they have an [[antibiotic]] effect that favours the activity of [[brewer's yeast]] over less desirable microorganisms; and they aid in "head retention", the length of time that the foam on top of the beer (the [[beer head]]) will last.<ref>{{cite book |url=https://books.google.com/books?id=8h4Ze5s6sFUC&pg=PA177 |title=Laboratory Manual of Food Microbiology |page=177 |author1=Neelima Garg |author2=K. L. Garg |author3=K. G. Mukerji |publisher=I. K. International Pvt Ltd |date=1 March 2010 |isbn=9789380578019 |access-date=1 August 2012 |archive-url=https://web.archive.org/web/20160424103623/https://books.google.com/books?id=8h4Ze5s6sFUC&pg=PA177&lpg=PA177 |archive-date=24 April 2016 |url-status=live }}</ref> The preservative in hops comes from the lupulin glands which contain soft resins with alpha and beta acids.<ref>{{Cite book|url=https://books.google.com/books?id=XRyxWu8rRnQC&q=alpha+and+beta+acids&pg=PA43|title=The Dictionary of Beer and Brewing
|publisher=Taylor & Francis |date=1998 |author1=Dan Rabin |author2=Carl Forget |isbn=9781579580780
}}</ref><ref>{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA317|title=Encyclopaedia of Brewing|page=317|author=Chris Boulton|publisher=John Wiley & Sons|date=20 May 2013|isbn=9781118598122|archive-url=https://web.archive.org/web/20160603004027/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA317|archive-date=3 June 2016|url-status=live}}</ref> Though much studied, the preservative nature of the soft resins is not yet fully understood, though it has been observed that unless stored at a cool temperature, the preservative nature will decrease.<ref>{{cite book|url=https://books.google.com/books?id=JcFri96bbpkC&pg=PA51|pages=51–54|title=Brewing|author=A. Chaston Chapman|publisher=Cambridge University Press|date=22 March 2012|isbn=9781107605954|archive-url=https://web.archive.org/web/20160501074725/https://books.google.com/books?id=JcFri96bbpkC&pg=PA51|archive-date=1 May 2016|url-status=live}}</ref><ref>{{cite web |url=http://cat.inist.fr/?aModele=afficheN&cpsidt=17772625 |title=A better control of beer properties by predicting acidity of hop iso-α-acids|author1=Blanco Carlos A. |author2=Rojas Antonio |author3=Caballero Pedro A. |author4=Ronda Felicidad |author5=Gomez Manuel |author6=Caballero |access-date=13 September 2008 |archive-url=https://web.archive.org/web/20110810071512/http://cat.inist.fr/?aModele=afficheN&cpsidt=17772625 |archive-date=10 August 2011 |url-status=live}}</ref> Brewing is the sole major commercial use of hops.<ref>{{cite book|author=A. H. Burgess|title=Hops: Botany, Cultivation and Utilization |publisher=Leonard Hill |date=1964 |isbn=978-0-471-12350-7}}</ref>

;Yeast
{{Main|Brewer's yeast|Saccharomyces cerevisiae|Saccharomyces pastorianus}}
Yeast is the [[microorganism]] that is responsible for fermentation in beer. Yeast [[metabolism|metabolises]] the sugars extracted from grains, which produces [[Ethanol|alcohol]] and [[carbon dioxide]], and thereby turns [[wort]] into beer. In addition to fermenting the beer, yeast influences the character and flavour.<ref>{{cite journal |author1=S. Ostergaard |author2=L. Olsson |author3=J. Nielsen |title=Metabolic Engineering of Saccharomyces cerevisiae Microbiol. Mol. Biol. Rev. 2000 64 |journal=Microbiology and Molecular Biology Reviews |date=March 2000 |volume=64 |issue=1 |pages=34–50 |doi=10.1128/mmbr.64.1.34-50.2000 |pmid=10704473 |pmc=98985 }}</ref>
The dominant types of yeast used to make beer are ''[[Saccharomyces cerevisiae]]'', known as ale yeast, and ''[[Saccharomyces pastorianus]]'', known as lager yeast;  ''[[Brettanomyces]]'' ferments [[lambic]]s,<ref>{{cite book  |title=Brewing |url=https://archive.org/details/brewingrscpaperb00horn |url-access=limited |pages=[https://archive.org/details/brewingrscpaperb00horn/page/n232 221]–222 |author=Ian Spencer Hornsey |publisher=Royal Society of Chemistry |date=25 November 1999 }}</ref> and ''[[Torulaspora delbrueckii]]'' ferments Bavarian [[Wheat beer#Weissbier|weissbier]].<ref>[http://web.mst.edu/~microbio/BIO221_2001/torulospora_delbrueckii.htm Web.mst.edu] {{Webarchive|url=https://web.archive.org/web/20110809212726/http://web.mst.edu/~microbio/BIO221_2001/torulospora_delbrueckii.htm |date=9 August 2011 }} David Horwitz, ''Torulaspora delbrueckii''. Retrieved 30 September 2008</ref> Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts, and a few styles such as [[lambic]]s still use this method today. [[Emil Christian Hansen]], a Danish biochemist employed by the [[Carlsberg Laboratory]], developed pure yeast [[Microbiological culture|cultures]] which were introduced into the Carlsberg brewery in 1883,<ref>{{cite book |url=https://books.google.com/books?id=QqnvNsgas20C&pg=PA601 |title=A History of Beer and Brewing |pages=601–604 |author=Ian S Hornsey |publisher=Royal Society of Chemistry |date=22 December 2003 |isbn=9780854046300 |access-date=1 August 2012 |archive-url=https://web.archive.org/web/20160610084753/https://books.google.com/books?id=QqnvNsgas20C&pg=PA601 |archive-date=10 June 2016 |url-status=live }}</ref> and pure yeast strains are now the main fermenting source used worldwide.<ref>{{cite book |url=https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA280 |title=Brewing |page=280 |author1=Michael Lewis |author2=Tom W. Young |publisher=Springer |date=31 October 2002 |access-date=1 August 2012 |isbn=9780306472749 |archive-url=https://web.archive.org/web/20160528220023/https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA280&lpg=PA280 |archive-date=28 May 2016 |url-status=live }}</ref>

;Clarifying agent
{{Main|Finings}}
Some brewers add one or more [[clarifying agent]]s to beer, which typically [[Precipitation (chemistry)|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 beer|bright]] and clean, rather than the cloudy appearance of ethnic and older styles of beer such as [[wheat beer]]s.<ref>{{cite web |url=http://www.beerhunter.com/documents/19133-000717.html |title=Michael Jackson's Beer Hunter&nbsp;– A pint of cloudy, please |publisher=Beerhunter.com |access-date=28 September 2008 |archive-url=https://web.archive.org/web/20080926132813/http://www.beerhunter.com/documents/19133-000717.html |archive-date=26 September 2008 |url-status=live }}</ref>

Examples of clarifying agents include [[isinglass]], obtained from [[swim bladder]]s of fish; [[Chondrus crispus|Irish moss]], a seaweed; kappa [[carrageenan]], from the seaweed ''[[kappaphycus]]''; [[Polyvinylpolypyrrolidone|polyclar]] (a commercial brand of clarifier); and [[gelatin]].<ref>[http://www.efsa.europa.eu/EFSA/efsa_locale-1178620753812_1178630797698.htm EFSA] {{Webarchive|url=https://web.archive.org/web/20070903235033/http://www.efsa.europa.eu/EFSA/efsa_locale-1178620753812_1178630797698.htm |date=3 September 2007 }} ''Opinion of the Scientific Panel on Dietetic Products, Nutrition and Allergies'', 23 August 2007. Retrieved 29 September 2008</ref> If a beer is marked "suitable for Vegans", it was generally clarified either with seaweed or with artificial agents,<ref>[http://www.food.gov.uk/multimedia/pdfs/consultationresponse/summrespvegi.pdf Food.gov.uk] {{webarchive |url=https://web.archive.org/web/20081002104412/http://www.food.gov.uk/multimedia/pdfs/consultationresponse/summrespvegi.pdf |date=2 October 2008 }}    ''Draft Guidance on the Use of the Terms 'Vegetarian' and 'Vegan' in Food Labelling: Consultation Responses'' pp71, 5 October 2005. Retrieved 29 September 2008</ref> although the "Fast Cask" method invented by [[Marston's Brewery|Marston's]] in 2009 may provide another method.<ref>{{cite web|url=http://www.beer-pages.com/protz/features/fast-cask.htm|author=Roger Protz|author-link=Roger Protz|title=Fast Cask|date=15 March 2010|access-date=19 June 2010|archive-url=https://web.archive.org/web/20100523092017/http://www.beer-pages.com/protz/features/fast-cask.htm|archive-date=23 May 2010|url-status=live}}</ref>

==Brewing process==
{{Brewing}}
There are several steps in the brewing process, which may include malting, mashing, lautering, [[#Boiling|boiling]], [[Fermentation in food processing|fermenting]], [[#Conditioning|conditioning]], [[#Filtering|filtering]], and [[#Packaging|packaging]].<ref>{{cite book |url=https://books.google.com/books?id=W8TjCNuwCjUC&pg=PT383 |title=Handbook of Food Science, Technology, And Engineering |page=383 |author=Yiu H. Hui |publisher=CRC Press |year=2006 |access-date=18 April 2012 |isbn=9780849398490 |archive-url=https://web.archive.org/web/20160506022837/https://books.google.com/books?id=W8TjCNuwCjUC&pg=PT383 |archive-date=6 May 2016 |url-status=live }}</ref> The [[brewing equipment]] needed to make beer has grown more sophisticated over time, and now covers most aspects of the brewing process.<ref>{{cite book |url=https://books.google.com/books?id=yj09YkztozoC&pg=PA26 |page=26| title=Beer For Dummies |author=Marty Nachel |publisher=John Wiley & Sons |date=3 January 2012 |isbn=9781118120309}}</ref><ref>{{cite book|url=https://books.google.com/books?id=0os_gIvG_ccC&pg=PA97  |title=Handbook of Brewing |page=79 |publisher=CRC Press |date=15 November 1994 |author=William Hardwick |isbn=9780849390357 }}</ref>

[[Malting]] is the process where barley grain is made ready for brewing.<ref>{{cite book |url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA563 |title=The Oxford Companion to Beer |page=563 |author1=John Hall |author2=Wolfgang David Lindell |publisher=Oxford University Press |date=7 October 2011 |access-date=18 April 2012 |isbn=9780195367133 |archive-url=https://web.archive.org/web/20160610053055/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA563 |archive-date=10 June 2016 |url-status=live }}</ref> Malting is broken down into three steps in order to help to release the starches in the barley.<ref>{{cite book |url=https://books.google.com/books?id=u3qc7aqWt9oC&pg=PA6 |title=The Science of Drinking: How Alcohol Affects Your Body and Mind |page=6 |author=Amitava Dasgupta |publisher=Rowman & Littlefield |date=16 April 2011 |access-date=18 April 2012 |isbn=9781442204119 |archive-url=https://web.archive.org/web/20160501110737/https://books.google.com/books?id=u3qc7aqWt9oC&pg=PA6 |archive-date=1 May 2016 |url-status=live }}</ref> First, during steeping, the grain is added to a vat with water and allowed to soak for approximately 40 hours.<ref name="malting">{{cite book |url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA564 |title=The Oxford Companion to Beer |page=564 |author1=John Hall |author2=Wolfgang David Lindell |publisher=Oxford University Press |date=7 October 2011 |access-date=18 April 2012 |isbn=9780195367133 |archive-url=https://web.archive.org/web/20160506064407/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA564 |archive-date=6 May 2016 |url-status=live }}</ref> During [[germination]], the grain is spread out on the floor of the germination room for around 5 days.<ref name="malting" /> The final part of malting is kilning when the malt goes through a very high temperature drying in a kiln; with gradual temperature increase over several hours.<ref>{{cite book|url=https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA176|page=176|title=Brewing|author1=Michael J. Lewis|author2=Tom W. Young|publisher=Springer|date=31 October 2002|isbn=9780306472749|archive-url=https://web.archive.org/web/20160425071449/https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA176|archive-date=25 April 2016|url-status=live}}</ref> When kilning is complete, the grains are now termed [[malt]], and they will be milled or crushed to break apart the kernels and expose the [[cotyledon]], which contains the majority of the carbohydrates and sugars; this makes it easier to extract the sugars during mashing.<ref name="Ale U Brewing Process">{{cite web|url=http://www.merchantduvin.com/pages/2_ale_university/aleu_brew_process.html |title=Ale University – Brewing Process |publisher=Merchant du Vin |year=2009 |access-date=12 November 2009 |url-status=dead |archive-url=https://web.archive.org/web/20091103020852/http://www.merchantduvin.com/pages/2_ale_university/aleu_brew_process.html |archive-date=3 November 2009 }}</ref>

[[Mashing]] 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]] which occurs between the temperatures {{convert|60|–|70|C|F}}.<ref>{{cite web |author=John Palmer |url=http://howtobrew.com/book/section-3/the-methods-of-mashing/single-temperature-infusion |title=Single Temperature Infusion |publisher=How to Brew |access-date=2018-09-20 |archive-url=https://web.archive.org/web/20180217023955/http://howtobrew.com/book/section-3/the-methods-of-mashing/single-temperature-infusion |archive-date=17 February 2018 |url-status=live }}</ref> The result of the mashing process is a sugar-rich liquid or [[Wort (brewing)|"wort"]], which is then strained through the bottom of the mash tun in a process known as [[lautering]]. Prior to lautering, the mash temperature may be raised to about {{convert|75|–|78|C|F}} (known as a mashout) to free up more starch and reduce mash viscosity. Additional water may be sprinkled on the grains to extract additional sugars (a process known as [[Sparging (beer)|sparging]]).<ref name="Goldhammer 2008">{{Cite book|author=Ted Goldammer|title=The Brewer's Handbook: The Complete Book To Brewing Beer |publisher=Apex |edition=2nd |isbn=978-0-9675212-3-7 |date=1 October 2008}}</ref>

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. This stage is where many chemical reactions take place, and where important decisions about the flavour, colour, and aroma of the beer are made.<ref name="Fosters">{{cite web|url=http://www.fosters.com.au/enjoy/beer/history_of_beer.htm |title=History of Beer |publisher=Foster's Group |date=July 2005 |url-status=dead |archive-url=https://web.archive.org/web/20060216203039/http://www.fosters.com.au/enjoy/beer/history_of_beer.htm |archive-date=16 February 2006 }}</ref> The boiling process serves to terminate enzymatic processes, [[Precipitation (chemistry)|precipitate]] proteins, [[isomerization|isomerize]] hop [[resin]]s, and concentrate and [[sterilization (microbiology)|sterilize]] the wort. Hops add flavour, [[odor|aroma]] and [[Bitter (taste)|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.<ref name="Hornsey 2004">{{Cite book|author=I. Hornsey |title=A History of Beer and Brewing |edition=1st|location=Washington D.C. |publisher=Royal Society of Chemistry |isbn=978-0-85404-630-0 |year=2004}}</ref>

After the whirlpool, the wort is drawn away from the compacted hop trub, and rapidly cooled via a [[heat exchanger]] to a temperature where yeast can be added. A variety of heat exchanger designs are used in breweries, with the most common a plate-style. Water or glycol run in channels in the opposite direction of the wort, causing a rapid drop in temperature. It is very important to quickly cool the wort to a level where yeast can be added safely as yeast is unable to grow in very high temperatures, and will start to die in temperatures above {{Convert|60|°C}}.<ref name="Ale U Brewing Process" /><ref>{{cite book |url=https://books.google.com/books?id=oKDNAwAAQBAJ&pg=PA41 |page=41 |title=The Oxford Handbook of Food Fermentations |author1=Charles W. Bamforth |author2=Robert Edwin Ward |publisher=Oxford University Press |date=2014 |isbn=9780199742707}}</ref> 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.<ref name="Fosters" /> When the yeast is added to the wort, the fermenting process begins, where the sugars turn into alcohol, [[carbon dioxide]] and other components. When the fermentation is complete the brewer may rack the beer into a new tank, called a conditioning tank.<ref name="Goldhammer 2008" /> Conditioning of the beer is the process in which the beer ages, the flavour becomes smoother, and flavours that are unwanted dissipate.<ref name="Hornsey 2004" /> After conditioning for a week to several months, the beer may be [[Filtered beer|filtered]] and [[carbonation|force carbonated]] for bottling,<ref>{{cite book|url=https://books.google.com/books?id=gYVLHMmplRcC&pg=PA176|title=The Oxford Companion to Beer|page=176|author=Garrett Oliver|publisher=Oxford University Press|date=7 October 2011|access-date=30 July 2012|isbn=9780195367133|author-link=Garrett Oliver|archive-url=https://web.archive.org/web/20160504141318/https://books.google.com/books?id=gYVLHMmplRcC&pg=PA176&lpg=PA176|archive-date=4 May 2016|url-status=live}}</ref> or [[Finings|fined]] in the [[Cask ale|cask]].<ref>{{cite book |url=https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA306 |title=Brewing |page=306 |author1=Michael Lewis |author2=Tom W. Young |publisher=Springer |date=31 October 2002 |access-date=30 July 2012 |isbn=9780306472749 |archive-url=https://web.archive.org/web/20160616203606/https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA306 |archive-date=16 June 2016 |url-status=live }}</ref>

==Mashing==
{{Main|Mashing}}
[[File:Mash Tun exhibit in the Brewery Museum at Burton-upon-Trent - geograph.org.uk - 2664334.jpg|left|thumb|A mash tun at the [[National Brewery Centre|Bass Museum]] in Burton-upon-Trent]]

Mashing is the process of combining a mix of milled grain (typically [[malt]]ed [[barley]] with [[Adjuncts|supplementary grains]] such as [[Maize|corn]], [[sorghum]], [[rye]] or wheat), known as the "grist" or "grain bill", and water, known as "liquor", and heating this mixture in a vessel called a "mash tun". Mashing is a form of steeping,<ref>{{cite book |url=https://books.google.com/books?id=yjLqQPU_DzYC&pg=PT197 |title=The Illustrated Guide to Brewing Beer |author=Matthew Schaefer |page=197 |publisher=Skyhorse Publishing Inc. |date=15 February 2012 |access-date=13 November 2012 |isbn=9781616084639 |archive-url=https://web.archive.org/web/20160629172405/https://books.google.com/books?id=yjLqQPU_DzYC&pg=PT197 |archive-date=29 June 2016 |url-status=live }}</ref> and defines the act of brewing, such as with making tea, [[sake]], and [[soy sauce]].<ref>{{cite book |url=https://books.google.com/books?id=mb0SZIYCXREC&pg=PA41 |title=Alcohol in Popular Culture: An Encyclopedia |author=Rachel Black |page=41 |publisher=ABC-CLIO |date=14 October 2010 |access-date=13 November 2012 |isbn=9780313380488 |archive-url=https://web.archive.org/web/20160624101218/https://books.google.com/books?id=mb0SZIYCXREC&pg=PA41 |archive-date=24 June 2016 |url-status=live }}</ref> Technically, wine, [[cider]] and [[mead]] are not brewed but rather [[vinified]], as there is no steeping process involving solids.<ref>{{cite journal|url=https://books.google.com/books?id=TlYFAAAAQAAJ&pg=RA1-PA120|journal=The Saturday Magazine|page=120|author=The Saturday Magazine|title=The Useful Arts No. X|date=September 1835|access-date=13 November 2012|archive-url=https://web.archive.org/web/20160503074345/https://books.google.com/books?id=TlYFAAAAQAAJ&pg=RA1-PA120|archive-date=3 May 2016|url-status=live}}</ref> Mashing allows the [[enzyme]]s in the malt to break down the [[starch]] in the grain into sugars, typically [[maltose]] to create a malty liquid called [[wort]].<ref>{{cite book |title=Foods and Nutrition Encyclopedia  |author=Audrey Ensminger |page=188 |publisher=[[CRC Press]] |year=1994 |isbn=978-0-8493-8980-1}}</ref> There are two main methods – [[infusion]] mashing, in which the grains are heated in one vessel; and [[decoction]] mashing, in which a proportion of the grains are boiled and then returned to the mash, raising the temperature.<ref>{{cite book|author=Dan Rabin|title=The Dictionary of Beer and Brewing |publisher=[[Taylor & Francis]] |page=180 |year=1998 |isbn=978-1-57958-078-0}}</ref> Mashing involves pauses at certain temperatures (notably {{convert|45|-|62|-|73|C|F|disp=or}}), and takes place in a "mash tun" – an insulated brewing vessel with a [[false bottom]].<ref name="Van den Steen">"Abdijbieren. Geestrijk erfgoed" by Jef Van den Steen</ref><ref>{{cite web|url=http://www.geocities.com/bierbrouwen/bereiding.html |archive-url=https://web.archive.org/web/20080419004815/http://www.geocities.com/bierbrouwen/bereiding.html |archive-date=19 April 2008 |title=Bier brouwen |date=19 April 2008 |access-date=15 December 2011}}</ref><ref>{{cite web |url=http://www.realbeer.com/jjpalmer/ch14.html |title=What is mashing? |publisher=Realbeer.com |access-date=15 December 2011 |archive-url=https://web.archive.org/web/20120106051734/http://realbeer.com/jjpalmer/ch14.html |archive-date=6 January 2012 |url-status=live }}</ref> 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]]s and then to fermentable sugars such as [[maltose]]. A mash rest from {{convert|49|-|55|C|F}} activates various [[protease]]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 [[maize|corn]] and rice, which are widely used in North American beers. A mash rest at {{convert|60|°C|°F|abbr=on}} 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 {{convert|65|-|71|C|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 favours [[β-amylase]] enzymes, producing more low-order sugars like [[maltotriose]], [[maltose]], and [[glucose]] 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 favours [[α-amylase]] enzymes, creating more higher-order sugars and [[dextrin]]s which are less fermentable by the yeast, so a fuller-bodied beer with less alcohol is the result. Duration and [[pH]] variances also affect the sugar composition of the resulting wort.<ref>{{cite book |author=Wolfgang Kunze|date=2004|title=Technology Brewing and Malting |url=https://archive.org/details/technologybrewin00kunz |url-access=limited |publisher=[[VLB Berlin]] |isbn=3-921690-49-8 |pages=[https://archive.org/details/technologybrewin00kunz/page/n214 214]–218}}</ref>

===Lautering===
[[File:Brasserie Ratz - 20140926 - Cuve à mélanger.jpg|thumb|Lauter tun]]
{{Main|Lautering}}

Lautering is the separation of the [[wort]] (the liquid containing the sugar extracted during mashing) from the grains.<ref name="Hui Smith">{{Cite book |author1=Yiu H. Hui |author2=J. Scott Smith |title=Food Processing: Principles and Applications |publisher=[[Wiley-Blackwell]] |date=2004 |isbn=978-0-8138-1942-6}}</ref> This is done either in a mash tun outfitted with a false bottom, in a lauter tun, or in 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 [[Lautering#Sparging|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 ground or milled cereal).<ref>{{cite web |url=http://www.beer-brewing.com/beer-brewing/wort_separation/lauter_tun.htm |title=Lauter Tun Use in Brewing Beer |publisher=beer-brewing.com |access-date=31 March 2010 |archive-url=https://web.archive.org/web/20100411074046/http://www.beer-brewing.com/beer-brewing/wort_separation/lauter_tun.htm |archive-date=11 April 2010 |url-status=dead}}</ref> The bed of grist that settles on it is the actual filter. Some lauter tuns have provision for rotating [[mash rake|rakes]] 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.<ref>{{cite book |author=T. Goldhammer |date=2008 |title=The Brewer's Handbook, 2nd edition |publisher=Apex |isbn=978-0-9675212-3-7| page=181}}</ref> 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.<ref>{{cite web |url=http://www.beer-brewing.com/beer-brewing/wort_separation/mash_filters.htm |title=Mash Filter Use in Brewing Beer |publisher=beer-brewing.com |access-date=31 March 2010 |archive-url=https://web.archive.org/web/20090617230127/http://www.beer-brewing.com/beer-brewing/wort_separation/mash_filters.htm |archive-date=17 June 2009 |url-status=dead}}</ref>

==Boiling==

After mashing, the beer [[wort]] is boiled with [[hops]] (and other flavourings if used) in a large tank known as a "copper" or brew kettle – though historically the mash vessel was used and is still in some small breweries.<ref>{{cite book |url=https://books.google.com/books?id=7eYLjJp0y7UC&pg=PA5 |title=Beer in the Middle Ages and the Renaissance |page=5 |author=Richard W. Unger |publisher=University of Pennsylvania Press |year=2007 |access-date=15 November 2012 |isbn=978-0812203745 |archive-url=https://web.archive.org/web/20160603192722/https://books.google.com/books?id=7eYLjJp0y7UC&pg=PA5 |archive-date=3 June 2016 |url-status=live }}</ref> The boiling process is where chemical reactions take place,<ref name="Fosters" /> including [[sterilization (microbiology)|sterilization]] of the wort to remove unwanted bacteria, releasing of hop flavours, bitterness and aroma compounds through [[isomerization]], stopping of enzymatic processes, [[Precipitation (chemistry)|precipitation]] of proteins, and concentration of the wort.<ref>{{cite book |url=https://books.google.com/books?id=ogXc9xTTCVsC&pg=PA63 |title=Froth!: The Science of Beer |page=63 |author=Mark Denny |publisher=JHU Press |date=6 May 2009 |access-date=15 November 2012 |isbn=9780801895692 |archive-url=https://web.archive.org/web/20160624144735/https://books.google.com/books?id=ogXc9xTTCVsC&pg=PA63 |archive-date=24 June 2016 |url-status=live }}</ref><ref name="Bamforth 2011">{{cite book |url=https://books.google.com/books?id=gYVLHMmplRcC&pg=PA141 |title=The Oxford Companion to Beer |pages=141–142 |author=Charles W. Bamforth |access-date=15 November 2012 |isbn=9780195367133 |date=9 September 2011 |publisher=Oxford University Press, USA |archive-url=https://web.archive.org/web/20160529073112/https://books.google.com/books?id=gYVLHMmplRcC&pg=PA141 |archive-date=29 May 2016 |url-status=live }}</ref> Finally, the vapours produced during the boil volatilise [[off-flavour]]s, including [[dimethyl sulfide]] precursors.<ref name="Bamforth 2011"/> The boil is conducted so that it is even and intense – a continuous "rolling boil".<ref name="Bamforth 2011" /> The boil on average lasts between 45 and 90 minutes, depending on its intensity, the hop addition schedule, and volume of water the brewer expects to evaporate.<ref>{{cite book|url=https://books.google.com/books?id=i__29xn-8t4C&pg=PA47|title=Essays in Brewing Science|page=47|author1=Michael J. Lewis|author2=Charles W. Bamforth|publisher=Springer|date=4 October 2006|access-date=15 November 2012|isbn=9780387330105|archive-url=https://web.archive.org/web/20160506071219/https://books.google.com/books?id=i__29xn-8t4C&pg=PA47|archive-date=6 May 2016|url-status=live}}</ref> At the end of the boil, solid particles in the hopped wort are separated out, usually in a vessel called a "whirlpool".<ref name="Hornsey 2004" />

===Brew kettle or copper===
[[File:Brasserie La Choulette 12-11-2006.jpg|thumb|Brew kettles at Brasserie La Choulette in France]]

Copper is the traditional material for the boiling vessel for two main reasons: firstly because copper transfers heat quickly and evenly; secondly because the bubbles produced during boiling, which could act as an insulator against the heat, do not cling to the surface of copper, so the wort is heated in a consistent manner.<ref name="Brew p272">{{cite book |url=https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA272 |title=Brewing |page=272 |author1=Michael Lewis |author2=Tom W. Young |publisher=Springer |year=2002 |isbn=9780306472749 |access-date=19 November 2015 |archive-url=https://web.archive.org/web/20160511062855/https://books.google.com/books?id=cr9Pv0gefCQC&pg=PA272&dq |archive-date=11 May 2016 |url-status=live }}</ref> 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 cleanup difficult. Most breweries use a steam-fired kettle, which uses steam jackets in the kettle to boil the wort.<ref name="Bamforth 2011" /> Breweries usually have a boiling unit either inside or outside of the kettle, usually a tall, thin cylinder with vertical tubes, called a calandria, through which wort is pumped.<ref name="Hampson 2011">{{cite book|url=https://books.google.com/books?id=gYVLHMmplRcC&pg=PA201|title=The Oxford Companion to Beer|page=201|author=Tim Hampson|publisher=Oxford University Press|date=9 September 2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20160502054817/https://books.google.com/books?id=gYVLHMmplRcC&pg=PA201|archive-date=2 May 2016|url-status=live}}</ref>

===Whirlpool===

At the end of the boil, solid particles in the hopped wort are separated out, usually in a vessel called a "whirlpool" or "settling tank".<ref name="Hornsey 2004" /><ref name="Klimovitz 2011"/> The whirlpool was devised by Henry Ranulph Hudston while working for the [[Molson Brewery]] in 1960 to utilise the so-called [[tea leaf paradox]] to force the denser solids known as "trub" (coagulated proteins, vegetable matter from hops) into a cone in the centre of the whirlpool tank.<ref>{{cite journal |author=W. Reed |date=1969 |title=The Whirlpool |journal=International Brewers' Journal |volume=105 |issue=2 |page=41 }}</ref><ref>{{cite web|url=http://www.mooseheadbeeracademy.com/teacups-albert-einstein-and-henry-hudston-moosehead-brewmaster/|work=mooseheadbeeracademy.com|title=Teacups, Albert Einstein, and Henry Hudston|author=Darrell Little|date=20 March 2013|access-date=7 December 2016|archive-url=https://web.archive.org/web/20170305002814/http://www.mooseheadbeeracademy.com/teacups-albert-einstein-and-henry-hudston-moosehead-brewmaster/|archive-date=5 March 2017|url-status=live}}</ref><ref name="Bamforth 2009">{{cite book|url=https://books.google.com/books?id=V3Sr4bbTH5oC&pg=PT170|page=170|title=Beer: Tap into the Art and Science of Brewing|author=Charles Bamforth|publisher=Oxford University Press|date=6 March 2009|isbn=9780199756360|access-date=7 December 2016|archive-url=https://web.archive.org/web/20191223130933/https://books.google.com/books?id=V3Sr4bbTH5oC&pg=PT170|archive-date=23 December 2019|url-status=live}}</ref> Whirlpool systems vary: smaller breweries tend to use the brew kettle, larger breweries use a separate tank,<ref name="Klimovitz 2011"/> and design will differ, with tank floors either flat, sloped, conical or with a cup in the centre.<ref>{{cite book|url=https://books.google.com/books?id=ciA6-YMTI-UC&pg=PA517|pages=517–518|title=Malting and Brewing Science: Hopped Wort and Beer|author=Tom W. Young|publisher=Springer|year=1982|isbn=9780834216846|archive-url=https://web.archive.org/web/20160506011544/https://books.google.com/books?id=ciA6-YMTI-UC&pg=PA517|archive-date=6 May 2016|url-status=live}}</ref> The principle in all is that by swirling the wort the [[centripetal force]] will push the trub into a cone at the centre of the bottom of the tank, where it can be easily removed.<ref name="Klimovitz 2011">{{cite book|url=https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA841|page=841|author=Ray Klimovitz|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=9 September 2011|isbn=9780199912100|archive-url=https://web.archive.org/web/20160527011846/https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA841|archive-date=27 May 2016|url-status=live}}</ref>

===Hopback===

A hopback is a traditional additional chamber that acts as a sieve or filter by using whole [[hops]] to clear debris (or "[[Trub (brewing)|trub]]") from the unfermented (or "green") [[wort]],<ref>{{cite book|url=https://books.google.com/books?id=SCg0ct2JKSoC&pg=PT25|page=25|title=Beer: A Gauge for Enthusiasts|author=Greg Duncan Powell|publisher=Allen & Unwin|date=2010|isbn=9781741968132|archive-url=https://web.archive.org/web/20191219200622/https://books.google.com/books?id=SCg0ct2JKSoC&pg=PT25|archive-date=19 December 2019|url-status=live}}</ref> as the whirlpool does, and also to increase hop aroma in the finished beer.<ref>{{cite book|url=https://books.google.com/books?id=gYVLHMmplRcC&pg=PA540|page=540|author=Chad Michael Yakobson|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=9 September 2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20160604055338/https://books.google.com/books?id=gYVLHMmplRcC&pg=PA540|archive-date=4 June 2016|url-status=live}}</ref><ref>{{cite book|url=https://books.google.com/books?id=MonpQW63TKcC&pg=PA127|title=Brewing|page=127|author=Ian Hornsey|publisher=Royal Society of Chemistry|date=2013|isbn=9781849736022|archive-url=https://web.archive.org/web/20160509224128/https://books.google.com/books?id=MonpQW63TKcC&pg=PA127|archive-date=9 May 2016|url-status=live}}</ref> It is a chamber between the brewing kettle and wort chiller. Hops 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. Hopbacks utilizing a sealed chamber facilitate maximum retention of volatile hop aroma compounds that would normally be driven off when the hops contact the hot wort.<ref>{{cite book|url=https://books.google.com/books?id=NB8NAQAAIAAJ&pg=PA23|page=23|title=The Brewing Industry: A Guide to Historical Records|author=Peter Mathias|publisher=Manchester University Press|date=1 January 1990|isbn=9780719030321|archive-url=https://web.archive.org/web/20160617050459/https://books.google.com/books?id=NB8NAQAAIAAJ&pg=PA23|archive-date=17 June 2016|url-status=live}}</ref> While a hopback has a similar filtering effect as a whirlpool, it operates differently: a whirlpool uses centrifugal forces, a hopback uses a layer of whole hops to act as a filter bed. Furthermore, while a whirlpool is useful only for the removal of pelleted hops (as flowers do not tend to separate as easily), in general hopbacks are used only for the removal of whole flower hops (as the particles left by pellets tend to make it through the hopback).<ref>{{cite book |url=https://books.google.com/books?id=ciA6-YMTI-UC&pg=PA516 |title=Malting and Brewing Science: Hopped Wort and Beer |pages=516–517 |author1=J.S. Hough |author2=D.E. Briggs |author3=R. Stevens |author4=Tom W. Young |publisher=Springer |date=31 August 1982 |access-date=31 July 2012 |isbn=9780834216846 |archive-url=https://web.archive.org/web/20160603232406/https://books.google.com/books?id=ciA6-YMTI-UC&pg=PA516&lpg=PA516 |archive-date=3 June 2016 |url-status=live }}</ref> The hopback has mainly been substituted in modern breweries by the whirlpool.<ref>{{cite book|url=https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA453|page=453|author=Paul Buttrick|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=9 September 2011|isbn=9780199912100|archive-url=https://web.archive.org/web/20160514132504/https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA453|archive-date=14 May 2016|url-status=live}}</ref>

===Wort cooling===
After the whirlpool, the wort must be brought down to fermentation temperatures {{convert|20|-|26|C|F}}<ref name="Van den Steen" /> before yeast is added. In modern breweries this is achieved through a plate [[heat exchanger]].<ref name=Plate>{{cite book |url=https://books.google.com/books?id=0os_gIvG_ccC&pg=PA312|page=312|title=Handbook of Brewing|editor=William Hardwick|publisher=CRC Press|date= 15 Nov 1994|isbn=978-0-8493-9035-7 }}</ref> A plate heat exchanger has sereral ridged plates, which form two separate paths. The wort is pumped into the heat exchanger, and goes through every other gap between the plates.<ref name=Plate/> The cooling medium, usually water from a [[cold liquor tank]], goes through the other gaps. The ridges in the plates ensure turbulent flow.<ref>{{cite web|url=https://theengineeringmindset.com/how-plate-heat-exchangers-work/|work=theengineeringmindset.com|title=How Plate Heat Exchangers Work|author=Paul Evans|date=5 July 2019}}</ref>  A good heat exchanger can drop {{Convert|95|°C}} wort to {{Convert|20|°C}} while warming the cooling medium from about {{Convert|10|°C}} to {{Convert|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 {{Convert|10|°C}}. After cooling, oxygen is often dissolved into the wort to revitalize the yeast and aid its reproduction.<ref>{{cite web|url= https://byo.com/article/aerating-wort-techniques/|work=byo.com|title=Aerating Wort Techniques|author=Jon Stika|year=2009}}</ref> 

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.<ref name="Kunze 2004">{{cite book|author=Wolfgang Kunze |date=2004 |title=Technology Brewing and Malting|url=https://archive.org/details/technologybrewin00kunz |url-access=limited |publisher=VLB Berlin|isbn=3-921690-49-8|page=[https://archive.org/details/technologybrewin00kunz/page/n299 302]}}</ref> 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.<ref name="Kunze 2004" />

==Fermenting {{anchor|Brewing#Fermenting}}==
[[File:Cuves de fermentations.jpg|thumb|upright|left|Modern closed fermentation vessels]]

[[Fermentation]] takes place in fermentation vessels which come in various forms, from enormous cylindroconical vessels, through open stone vessels, to wooden vats.<ref name="ferm1">{{cite book|chapter-url=https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA347|title=The Oxford Companion to Beer|chapter=Fermentation vessels|author=Anders Brinch Kissmeyer |author2=Garrett Oliver|pages=347–351|publisher=Oxford University Press |date=9 September 2011|isbn=9780199912100}}</ref><ref name="ferm2">{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA236|page=236|title=Encyclopaedia of Brewing|publisher=John Wiley & Sons|date=20 May 2013|author=Chris Boulton|isbn=9781118598122|archive-url=https://web.archive.org/web/20160508235440/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA236&dq=|archive-date=8 May 2016|url-status=live}}</ref><ref name="ferm3">{{cite book|url=https://books.google.com/books?id=QpDVsu-vaBcC&pg=PT294|page=294|title=Brewing Yeast and Fermentation|author=Chris Boulton|author2=David Quain|publisher=John Wiley & Sons|date=25 April 2013|isbn=9781118685341|archive-url=https://web.archive.org/web/20160528201954/https://books.google.com/books?id=QpDVsu-vaBcC&pg=PT294&dq=|archive-date=28 May 2016|url-status=live}}</ref> After the wort is cooled and [[aerated]] – usually with [[Asepsis|sterile]] air – yeast is added to it, and it begins to ferment. It is during this stage that sugars won from the [[malt]] are converted into alcohol and [[carbon dioxide]], and the product can be called beer for the first time.

Most breweries today use cylindroconical vessels, or CCVs, which have a conical bottom and a cylindrical top. The cone's angle 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.<ref name="ferm1"/><ref name="ferm2"/><ref name="ferm3"/>
{{-}}

===Fermentation methods===
{{See also|Beer style}}
[[File:Black Sheep Brewery Tour.jpg|thumb|right|Open vessels showing fermentation taking place]]

There are three main fermentation methods, [[#Warm fermentation|warm]], [[#Cool fermentation|cool]], and [[#Spontaneous fermentation|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 ale|cask]] or in the [[#Bottle conditioning|bottle]].<ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA346|page=346|author=George Philliskirk|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20191202093529/https://books.google.co.uk/books?id=Ga4MYyZq-RMC&pg=PA346|archive-date=2 December 2019|url-status=live}}</ref>

Brewing yeasts are traditionally classed as "top-cropping" (or "top-fermenting") and "bottom-cropping" (or "bottom-fermenting"); the yeasts classed as top-fermenting are generally used in warm fermentations, where they ferment quickly, and the yeasts classed as bottom-fermenting are used in cooler fermentations where they ferment more slowly.<ref>{{cite book |url=https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |title=Handbook of Brewing |page=84 |author1=F. G. Priest |author2=Graham G. Stewart |publisher=CRC Press |date=22 February 2006 |access-date=16 July 2012 |isbn=9780824726577 |archive-url=https://web.archive.org/web/20160520045343/https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |archive-date=20 May 2016 |url-status=live }}</ref> Yeast were termed top or bottom cropping, because the yeast was collected from the top or bottom of the fermenting wort to be reused for the next brew.<ref name="Tom Colicchio 2011">{{cite book|author=Tom Colicchio|title=The Oxford Companion to Beer|publisher=Oxford University Press|year=2011}}</ref> This terminology is somewhat inappropriate in the modern era; after the widespread application of brewing mycology it was discovered that the two separate collecting methods involved two different yeast species that favoured different temperature regimes, namely ''Saccharomyces cerevisiae'' in top-cropping at warmer temperatures and ''Saccharomyces pastorianus'' in bottom-cropping at cooler temperatures.<ref>{{cite book|author=Emil Christian Hansen|title=Practical studies in fermentation: being contributions to the life history of micro-organisms|url=https://archive.org/details/practicalstudies00hansrich|publisher=E. & FN Spon|year=1896|access-date=10 November 2019|archive-url=https://web.archive.org/web/20070403050128/http://www.archive.org/details/practicalstudies00hansrich|archive-date=3 April 2007|url-status=live}}</ref> As brewing methods changed in the 20th century, cylindro-conical fermenting vessels became the norm and the collection of yeast for both ''Saccharomyces'' species is done from the bottom of the fermenter. Thus the method of collection no longer implies a species association. There are a few remaining breweries who collect yeast in the top-cropping method, such as Samuel Smiths brewery in Yorkshire, Marstons in Staffordshire and several German hefeweizen producers.<ref name="Tom Colicchio 2011"/>

For both types, yeast is fully distributed through the beer while it is fermenting, and both equally [[yeast flocculation|flocculate]] (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 that may also exhibit chain forming (the failure of budded cells to break from the mother cell), which is in the technical sense 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]] in the shortest amount of time; brewing yeast strains act slower, but tend to tolerate higher alcohol concentrations (normally 12–15% [[Alcohol by volume|abv]] is the maximum, though under special treatment some ethanol-tolerant strains can be coaxed up to around 20%).<ref>{{cite book |url=https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA331 |page=331 |author1=Charles W. Bamforth |author2=Chris White |title=The Oxford Companion to Beer |publisher=Oxford University Press |date=9 September 2011 |isbn=9780199912100 |access-date=19 November 2015 |archive-url=https://web.archive.org/web/20160430231035/https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA331 |archive-date=30 April 2016 |url-status=live }}</ref> Modern quantitative genomics has revealed the complexity of ''Saccharomyces'' species to the extent that yeasts involved in beer and wine production commonly involve hybrids of so-called pure species. As such, the yeasts involved in what has been typically called top-cropping or top-fermenting ale may be both ''Saccharomyces cerevisiae'' and complex hybrids of ''Saccharomyces cerevisiae'' and ''Saccharomyces kudriavzevii''. Three notable ales, [[Chimay Brewery|Chimay]], [[Orval Brewery#Beers|Orval]] and [[Westmalle Brewery|Westmalle]], are fermented with these hybrid strains, which are identical to wine yeasts from Switzerland.<ref>González, Sara S., Eladio Barrio, and Amparo Querol. "Molecular characterization of new natural hybrids of Saccharomyces cerevisiae and S. kudriavzevii in brewing". ''Applied and Environmental Microbiology'' 74.8 (2008): 2314–2320.</ref>

====Warm fermentation{{anchor|Warm fermentation}}{{anchor|Warm fermenting}}====

In general, yeasts such as ''[[Saccharomyces cerevisiae]]'' are fermented at warm temperatures between {{convert|15|and|20|C|F}}, occasionally as high as {{convert|24|°C|°F|abbr=on}},<ref>{{cite book|author1=Andrew G.H. Lea |author2=John Raymond Piggott |author3=John R. Piggott |title=Fermented Beverage Production|publisher=[[Springer Science+Business Media|Kluwer Academic/Plenum Publishers]] |date=2003 |isbn=0-306-47706-8 |pages=43–44}}</ref> while the yeast used by [[Dupont Brewery|Brasserie Dupont]] for [[saison]] ferments even higher at {{convert|29|to|35|C|F|0}}.<ref>''Farmhouse Ales: Culture and Craftsmanship in the European Tradition'', pages 168–173, Phil Markowski, Brewers Publications (2004), {{ISBN|0-937381-84-5}}</ref> They generally form a foam on the surface of the fermenting beer, which is called [[barm]], as during the fermentation process its [[hydrophobic]] surface causes the flocs to adhere to CO<sub>2</sub> and rise; because of this, they are often referred to as "top-cropping" or "top-fermenting"<ref>{{cite book|author1=Andrew G.H. Lea |author2=John Raymond Piggott |author3=John R. Piggott |title=Fermented Beverage Production|publisher=[[Springer Science+Business Media|Kluwer Academic/Plenum Publishers]]|date=2003|isbn=0-306-47706-8|page=43}}</ref> – though this distinction is less clear in modern brewing with the use of cylindro-conical tanks.<ref name="Bamforth 2005 66">{{cite book|author=Charles W. Bamforth|title=Food, Fermentation and Micro-organisms |page=66 |publisher=[[Wiley-Blackwell]] |year=2005 |isbn=978-0-632-05987-4}}</ref> Generally, warm-fermented beers, which are usually termed [[ale]], are ready to drink within three weeks after the beginning of fermentation, although some brewers will condition or mature them for several months.<ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA22|page=22|author=Garrett Oliver|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|author-link=Garrett Oliver|access-date=26 August 2019|archive-url=https://web.archive.org/web/20191227144338/https://books.google.co.uk/books?id=Ga4MYyZq-RMC&pg=PA22|archive-date=27 December 2019|url-status=live}}</ref>

====Cool fermentation====
{{anchor|Cool fermentation}}{{anchor|Cool fermenting}}
{{Main|Lager}}

When a beer has been brewed using a cool fermentation of around {{convert|10|°C|°F|abbr=on}}, compared to typical warm fermentation temperatures of {{convert|18|°C|°F|abbr=on}},<ref>{{cite book|url=https://books.google.com/books?id=Q82QAwAAQBAJ&pg=PT114|page=94|title=Yeast: The Practical Guide to Beer Fermentation|author=Chris White, Jamil Zainasheff|publisher=Brewers Publications|date=1 February 2010|isbn=9781938469060|archive-url=https://web.archive.org/web/20191222170637/https://books.google.com/books?id=Q82QAwAAQBAJ&pg=PT114|archive-date=22 December 2019|url-status=live}}</ref><ref>{{cite book|url=https://archive.org/details/palealehistorybr0000fost|url-access=registration|page=[https://archive.org/details/palealehistorybr0000fost/page/185 185]|title=Pale Ale|author=Terry Foster|publisher=Brewers Publications|date=7 April 1999|isbn=9781938469251}}</ref> then stored (or lagered) for typically several weeks (or months) at temperatures close to [[freezing]] point, it is termed a "[[lager]]".<ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA533|page=533|author=Garrett Oliver|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|author-link=Garrett Oliver|access-date=19 November 2015|archive-url=https://web.archive.org/web/20160528215325/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA533|archive-date=28 May 2016|url-status=live}}</ref> During the lagering or storage phase several flavour components developed during fermentation dissipate, resulting in a "cleaner" flavour.<ref>{{cite book|url=https://books.google.com/books?id=pkzx2TeYYT8C&pg=RA1-PA970|page=970|title=Comprehensive Natural Products II: Chemistry and Biology|author=Craig Townsend|publisher=Elsevier|date=2010|isbn=9780080453828|archive-url=https://web.archive.org/web/20191221030510/https://books.google.com/books?id=pkzx2TeYYT8C&pg=RA1-PA970|archive-date=21 December 2019|url-status=live}}</ref><ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA532|page=532|author=Garrett Oliver|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|author-link=Garrett Oliver|access-date=30 August 2017|archive-url=https://web.archive.org/web/20191219235900/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA532|archive-date=19 December 2019|url-status=live}}</ref> Though it is the slow, cool fermentation and cold conditioning (or lagering) that defines the character of lager,<ref>{{cite book|url=https://books.google.com/books?id=CazaCgAAQBAJ&pg=PR21|page=xxi|title=New Brewing Lager Beer|author=Gregory J. Noonan|publisher=Brewers Publications|date=17 September 2003|isbn=9781938469237|archive-url=https://web.archive.org/web/20191222040341/https://books.google.com/books?id=CazaCgAAQBAJ&pg=PR21|archive-date=22 December 2019|url-status=live}}</ref> the main technical difference is with the yeast generally used, which is ''[[Saccharomyces pastorianus]]''.<ref>{{cite book |chapter-url=https://books.google.com/books?id=hBO3N5qLTEIC&pg=PA89|page=89|title=Beer in Health and Disease Prevention |chapter=8 The Brewer's Yeast Genome |author=Sandra Rainieri |publisher=Academic Press |date=28 April 2011 |isbn=9780080920498}}</ref> Technical differences include the ability of lager yeast to metabolize [[melibiose]],<ref name="Boekhout Robert 2003" /> and the tendency to settle at the bottom of the fermenter (though ale yeasts can also become bottom settling by selection);<ref name="Boekhout Robert 2003">{{cite book|url=https://books.google.com/books?id=XqmjAgAAQBAJ&pg=PA349|page=349|title=Yeasts in Food|author=T Boekhout, V Robert|publisher=Elsevier|date=7 May 2003|isbn=9781845698485|archive-url=https://web.archive.org/web/20191223172609/https://books.google.com/books?id=XqmjAgAAQBAJ&pg=PA349|archive-date=23 December 2019|url-status=live}}</ref> though these technical differences are not considered by scientists to be influential in the character or flavour of the finished beer, brewers feel otherwise – sometimes cultivating their own yeast strains which may suit their brewing equipment or for a particular purpose, such as brewing beers with a high abv.<ref>{{cite book |title=Brewing: science and practice |author=Briggs, Dennis Edward |display-authors=et al |publisher=Elsevier |date= 2004|page=123}}</ref><ref>{{cite book|url=https://books.google.com/books?id=f--1V1ftgtsC&pg=PA132|page=132|title=Kirk-Othmer Food and Feed Technology: Volume 1|publisher=John Wiley & Sons|date=2007|isbn=9780470174487|archive-url=https://web.archive.org/web/20191222163820/https://books.google.com/books?id=f--1V1ftgtsC&pg=PA132|archive-date=22 December 2019|url-status=live}}</ref><ref>{{cite web|url=https://www.businessinbrighton.org.uk/blog/2013/11/08/harveys-let-us-some-brewing-secrets|title=Harveys let us in on some brewing secrets|work=businessinbrighton.org.uk|author=Dan Rose|access-date=27 January 2017|archive-url=https://web.archive.org/web/20170202061613/https://www.businessinbrighton.org.uk/blog/2013/11/08/harveys-let-us-some-brewing-secrets|archive-date=2 February 2017|url-status=live}}</ref><ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA331|page=331|author=Chris White|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=9 September 2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20191228080342/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA331|archive-date=28 December 2019|url-status=live}}</ref>
[[File:Timmermans.jpg|thumb|200px|Spontaneous fermentation at [[Timmermans Brewery|Timmermans]] in Belgium]]
Brewers in [[Bavaria]] had for centuries been selecting cold-fermenting 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. A sample of these Bavarian yeasts was sent from the Spaten brewery in Munich to the Carlsberg brewery in Copenhagen in 1845 who began brewing with it. In 1883 Emile Hansen completed a study on pure yeast culture isolation and the pure strain obtained from Spaten went into industrial production in 1884 as Carlsberg yeast No 1. Another specialized pure yeast production plant was installed at the Heineken Brewery in Rotterdam the following year and together they began the supply of pure cultured yeast to brewers across Europe.<ref>Meussdoerffer, Franz G. "A comprehensive history of beer brewing". ''Handbook of brewing: processes, technology, markets'' (2009): 1–42.</ref><ref>Boulton, Christopher, and David Quain. ''Brewing yeast and fermentation''. John Wiley & Sons, 2008.</ref> This yeast strain was originally classified as ''Saccharomyces carlsbergensis'', a now defunct species name which has been superseded by the currently accepted taxonomic classification ''Saccharomyces pastorianus''.<ref>{{cite book|url=https://books.google.com/books?id=Y4RgCgAAQBAJ&pg=PA428|page=428|title=Advances in Bioprocess Technology|author=Pogaku Ravindra|publisher=Springer|date=13 August 2015|isbn=9783319179155|archive-url=https://web.archive.org/web/20191221202844/https://books.google.com/books?id=Y4RgCgAAQBAJ&pg=PA428|archive-date=21 December 2019|url-status=live}}</ref>

====Spontaneous fermentation====
[[Lambic]] beers are historically brewed in [[Brussels]] and the nearby [[Pajottenland]] region of Belgium without any yeast inoculation.<ref>{{cite book|url=https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA536|title=The Oxford Companion to Beer|author=Bill Taylor|page=536|publisher=Oxford University Press|date=9 September 2011|access-date=14 June 2013|isbn=9780199912100|archive-url=https://web.archive.org/web/20160516125550/https://books.google.com/books?id=oWQdjnVo2B0C&pg=PA536|archive-date=16 May 2016|url-status=live}}</ref><ref>{{cite book |url=https://books.google.com/books?id=sGz6wEwkBOwC&pg=PA56-IA7 |title=The Brewmaster's Table |author=Garrett Oliver |page=62 |publisher=HarperCollins |date=19 October 2010 |access-date=14 June 2013 |isbn=9780062042835 |author-link=Garrett Oliver |archive-url=https://web.archive.org/web/20160603161532/https://books.google.com/books?id=sGz6wEwkBOwC&pg=PA56-IA7&dq |archive-date=3 June 2016 |url-status=live }}</ref> The wort is cooled in open vats (called "[[coolship]]s"), where the yeasts and [[microbiota]] present in the brewery (such as ''[[Brettanomyces]]'')<ref name="Verachtert 1995">{{Cite journal|vauthors=Verachtert H, Iserentant D |year=1995 |title=Properties of Belgian acid beers and their microflora. 1. The production of gueuze and related refreshing acid beers |journal=Cerevesia |volume=20 |issue=1 |pages=37–42}}</ref> are allowed to settle to create a spontaneous fermentation,<ref name="Oxford">{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA265|page=265|author=George Philliskirk|title=The Oxford Companion to Beer|publisher=Oxford University Press|date=2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20191224044414/https://books.google.co.uk/books?id=Ga4MYyZq-RMC&pg=PA265|archive-date=24 December 2019|url-status=live}}</ref> and are then conditioned or matured in oak barrels for typically one to three years.<ref>{{cite journal |title=The Microbial Diversity of Traditional Spontaneously Fermented Lambic Beer |volume=9 |issue=4 |pages=e95384 |author1=Freek Spitaels |author2=Anneleen D. Wieme |display-authors=etal |date=18 April 2014 |journal=[[PLoS ONE]] |pmc=3991685 |pmid=24748344 |doi=10.1371/journal.pone.0095384 |bibcode=2014PLoSO...995384S|doi-access=free }}</ref>

==Conditioning==
[[File:Anchor Brewing Company conditioning tanks.JPG|thumb|left|Conditioning tanks at [[Anchor Brewing Company]]]]

After an initial or primary fermentation, beer is ''conditioned'', matured or aged,<ref>{{cite book |url=https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |title=Handbook of Brewing |page=86 |author1=F. G. Priest |author2=Graham G. Stewart |publisher=CRC Press |date=22 February 2006 |access-date=16 July 2012 |isbn=9780824726577 |archive-url=https://web.archive.org/web/20160520045343/https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |archive-date=20 May 2016 |url-status=live }}</ref> in one of several ways,<ref>{{cite book |url=https://books.google.com/books?id=DvNhR0xfHtMC&pg=PA141 |title=Brewing |page=141 |author=Ian Spencer Hornsey |publisher=Royal Society of Chemistry |date=25 November 1999 |access-date=16 July 2012 |isbn=9780854045686 |archive-url=https://web.archive.org/web/20160427191135/https://books.google.com/books?id=DvNhR0xfHtMC&pg=PA141 |archive-date=27 April 2016 |url-status=live }}</ref> which can take from 2 to 4 weeks, several months, or several years, depending on the brewer's intention for the beer. The beer is usually transferred into a second container, so that it is no longer exposed to the dead yeast and other debris (also known as "[[Trub (brewing)|trub]]") that have settled to the bottom of the primary fermenter. This prevents the formation of unwanted flavours and harmful compounds such as [[acetaldehyde]].<ref>{{cite book |url=https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA308 |title=Handbook of Brewing |page=308 |author1=F. G. Priest |author2=Graham G. Stewart |publisher=CRC Press |date=22 February 2006 |access-date=16 July 2012 |isbn=9780824726577 |archive-url=https://web.archive.org/web/20160511024453/https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA308 |archive-date=11 May 2016 |url-status=live }}</ref>

;Kräusening
Kräusening (pronounced {{respell|KROY|zen|ing}}<ref>{{cite web |work=[[Merriam-Webster]] |access-date=13 April 2023 |url=https://www.merriam-webster.com/dictionary/krausen |title=Definition of KRAUSEN }}</ref>) is a conditioning method in which fermenting [[wort]] is added to the finished beer.<ref name="Thomas 2011">{{cite book |url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA521 |title=The Oxford Companion to Beer |author=Keith Thomas |publisher=Oxford University Press |date=7 October 2011 |access-date=16 July 2012 |isbn=9780195367133 |archive-url=https://web.archive.org/web/20160517000817/https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA521 |archive-date=17 May 2016 |url-status=live }}</ref> The active yeast will restart fermentation in the finished beer, and so introduce fresh carbon dioxide; the conditioning tank will be then sealed so that the carbon dioxide is dissolved into the beer producing a lively "condition" or level of carbonation.<ref name="Thomas 2011"/> The kräusening method may also be used to condition bottled beer.<ref name="Thomas 2011"/>

;Lagering
[[Lager]]s are stored at cellar temperature or below for 1–6 months while still on the yeast.<ref>Briggs, D.E.; Boulton, C.A.; Brookes, P. A.; and Stevens, R. ''Brewing'', 2004, CRC. {{ISBN|0-8493-2547-1}} p. 5.</ref> The process of storing, or conditioning, or maturing, or aging a beer at a low temperature for a long period is called "lagering", and while it is associated with lagers, the process may also be done with ales, with the same result – that of cleaning up various chemicals, acids and compounds.<ref>{{cite book |chapter-url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA533 |title=The Oxford Companion to Beer|chapter=Lagering|author=Horst Dornbusch |pages=533–534 |publisher=Oxford University Press|date=9 September 2011 |access-date=8 April 2013 |isbn=9780195367133}}</ref>

;Secondary fermentation{{anchor|Brewing#Secondary fermentation}}
During secondary fermentation, most of the remaining yeast will settle to the bottom of the second fermenter, yielding a less hazy product.<ref>{{cite book |url=https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |title=Handbook of Brewing |page=532 |author1=F. G. Priest |author2=Graham G. Stewart |publisher=CRC Press |date=22 February 2006 |access-date=16 July 2012 |isbn=9780824726577 |archive-url=https://web.archive.org/web/20160520045343/https://books.google.com/books?id=TIYbNdrIsPEC&pg=PA86 |archive-date=20 May 2016 |url-status=live }}</ref>

;{{anchor|Bottle conditioning}}Bottle fermentation
Some beers undergo an additional fermentation in the bottle giving natural carbonation.<ref>{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA79|title=Encyclopaedia of Brewing|page=79|author=Christopher M. Boulton|publisher=Wiley|date=20 May 2013|access-date=14 June 2013|isbn=9781118598122|archive-url=https://web.archive.org/web/20160505233917/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA79|archive-date=5 May 2016|url-status=live}}</ref> This may be a second and/or third fermentation. They are bottled with a viable yeast population in suspension. If there is no residual fermentable sugar left, sugar or wort or both may be added in a process known as priming. The resulting fermentation generates [[carbon dioxide|CO<sub>2</sub>]] that is trapped in the bottle, remaining in solution and providing natural carbonation. Bottle-conditioned beers may be either filled unfiltered direct from the fermentation or conditioning tank, or filtered and then reseeded with yeast.<ref>{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA80|title=Encyclopaedia of Brewing|page=80|author=Christopher M. Boulton|publisher=Wiley|date=20 May 2013|access-date=14 June 2013|isbn=9781118598122|archive-url=https://web.archive.org/web/20160519034408/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA80|archive-date=19 May 2016|url-status=live}}</ref>

;Cask conditioning
[[File:Didsbury Beer Festival 2013 - On a Whim (10861199193).jpg|thumb|200px|Cask ales with gravity dispense at a beer festival]]

Cask ale (or cask-conditioned beer) is [[filtration|unfiltered]], [[pasteurization|unpasteurised]] beer that is conditioned by a secondary fermentation in a metal, plastic or [[Beer from the wood|wooden]] cask. It is dispensed from the cask by being either poured from a tap by gravity, or pumped up from a cellar via a [[beer engine]] (hand pump).<ref>{{cite book|url=https://books.google.com/books?id=DvNhR0xfHtMC&pg=PA150|pages=150–151|title=Brewing|author=Ian Spencer Hornsey|publisher=Royal Society of Chemistry|date=1 January 1999|isbn=9780854045686|archive-url=https://web.archive.org/web/20160611021750/https://books.google.com/books?id=DvNhR0xfHtMC&pg=PA150|archive-date=11 June 2016|url-status=live}}</ref> Sometimes a [[cask breather]] is used to keep the beer fresh by allowing carbon dioxide to replace oxygen as the beer is drawn off the cask.<ref>{{cite book|url=https://books.google.com/books?id=uWXcajHd3W0C&pg=PA109|page=150|title=Encyclopaedia of Brewing|publisher=John Wiley & Sons|date=20 May 2013|isbn=9781118598122|archive-url=https://web.archive.org/web/20160514044502/https://books.google.com/books?id=uWXcajHd3W0C&pg=PA109|archive-date=14 May 2016|url-status=live}}</ref> Until 2018, the [[Campaign for Real Ale]] (CAMRA) defined real ale as beer "served without the use of [[carbonation|extraneous carbon dioxide]]", which would disallow the use of a cask breather,<ref>{{cite book|url=https://books.google.com/books?id=104W8SNEd9kC&pg=PA299|page=299|title=Man Walks into a Pub|author=Pete Brown|publisher=Pan Macmillan|date=11 August 2011|isbn=9780330536806|archive-url=https://web.archive.org/web/20160723000804/https://books.google.com/books?id=104W8SNEd9kC&pg=PA299|archive-date=23 July 2016|url-status=live}}</ref> a policy which was reversed in April 2018 to allow beer served with the use of cask breathers to meet its definition of real ale.<ref>{{Cite web|url=https://camra.org.uk/press_release/camra-looks-to-the-future-as-its-members-call-for-positive-change/|title=CAMRA looks to the future as its members call for positive change|website=CAMRA - Campaign for Real Ale|language=en-GB|access-date=2020-02-02|archive-url=https://web.archive.org/web/20200202105156/https://camra.org.uk/press_release/camra-looks-to-the-future-as-its-members-call-for-positive-change/|archive-date=2 February 2020|url-status=live}}</ref>

;Barrel-ageing
{{Main|Barrel-aged beer}}

Barrel-ageing ([[American English|US:]] Barrel aging) is the process of ageing beer in [[barrel|wooden barrels]] to achieve a variety of effects in the final product. [[Sour beer]]s such as [[lambic]]s are fully fermented in wood, while other beers are aged in barrels which were previously used for maturing [[wine]]s or [[distilled beverage|spirits]]. In 2016 "Craft Beer and Brewing" wrote: "Barrel-aged beers are so trendy that nearly every taphouse and beer store has a section of them.<ref>{{Cite web |url=https://beerandbrewing.com/single-barrel-double-barrel-no-barrel/ |title=Craft Beer and Brewing. ''Single Barrel, Double Barrel? No Barrel!'' |access-date=26 November 2019 |archive-url=https://web.archive.org/web/20191224042150/https://beerandbrewing.com/single-barrel-double-barrel-no-barrel/ |archive-date=24 December 2019 |url-status=live }}</ref>

==Filtering==
{{Main|Filtered beer}}
[[File:Diatomaceous Earth.jpg|thumb|[[Diatomaceous earth]], used to create a [[Diatomaceous earth filtration|filtration bed]]]]

Filtering stabilises the flavour of beer, holding it at a point acceptable to the brewer, and preventing further development from the yeast, which under poor conditions can release negative components and flavours.<ref>{{cite book|chapter-url=https://link.springer.com/chapter/10.1007/978-1-4615-0187-9_16|chapter=Filtration and Stabilization of Beers|pages=365–366 |title=Fermented Beverage Production|publisher=Springer Science+Business Media |date=2003|author1=J. Freeman |author2=M. T. McKechnie|doi=10.1007/978-1-4615-0187-9_16|isbn=978-0-306-47706-5}}</ref> Filtering also removes haze, clearing the beer, and so giving it a "polished shine and brilliance".<ref>{{cite book|url=https://books.google.com/books?id=Ga4MYyZq-RMC&pg=PA352|title=The Oxford Companion to Beer|page=352|author=Jeff S. Nickel|publisher=Oxford University Press|date=9 September 2011|isbn=9780195367133|archive-url=https://web.archive.org/web/20191222165203/https://books.google.co.uk/books?id=Ga4MYyZq-RMC&pg=PA352|archive-date=22 December 2019|url-status=live}}</ref> Beer with a clear appearance has been commercially desirable for brewers since the development of glass vessels for storing and drinking beer, along with the commercial success of [[pale lager]], which – due to the [[lager]]ing process in which haze and particles settle to the bottom of the tank and so the beer "[[drops bright]]" (clears) – has a natural bright appearance and shine.<ref>{{cite book|url=https://archive.org/details/atextbookscienc00morrgoog/page/n424/mode/1up?view=theater|page=405|title=The Science of Brewing|author1=Edward Ralph Moritz |author2=George Harris Morris |date=1891|publisher=E. & F. N. Spon}}</ref> 

There are several forms of filters; they may be in the form of sheets or "candles", or they may be a fine powder such as [[diatomaceous earth]] (also called kieselguhr),<ref>{{cite book|url=https://books.google.com/books?id=oZY9EQAAQBAJ&pg=PA441|title=Elastomers and Rubber Compounding Materials|author=Rohit Manglik|page=441|publisher=EduGorilla|date=6 Jan 2024|isbn=978-93-6906-436-6 }}</ref> which is added to the beer to form a filtration bed which allows liquid to pass, but holds onto suspended particles such as yeast.<ref>{{cite book|url=https://books.google.com/books?id=HGqFDQAAQBAJ&pg=PT251|page=251|title=Brewing – A Practical Approach|author=Bijay Bahadur|publisher=Notion Press|date= 18 Nov 2016|isbn=9781946204776}}</ref> Filters range from rough filters that remove much of the yeast and any solids (e.g., hops, grain particles) left in the beer,<ref>{{cite book|url=https://books.google.com/books?id=Ut3LBQAAQBAJ&pg=PA539|page=539|title=Handbook of Brewing, Second Edition|author1=Graham G. Stewart|author2= Fergus G. Priest|publisher=CRC Press|date= 22 Feb 2006|isbn=9781420015171}}</ref> to filters tight enough to strain colour and body from the beer.{{fact|date=January 2022}} Filtration ratings are divided into rough, fine, and sterile.{{fact|date=January 2022}} Rough filtration leaves some cloudiness in the beer, but it is noticeably clearer than unfiltered beer.{{fact|date=January 2022}} Fine filtration removes almost all cloudiness.{{fact|date=January 2022}} Sterile filtration removes almost all microorganisms.{{fact|date=January 2022}}

;Sheet (pad) filters
These filters use sheets that allow only particles smaller than a given size to pass through. The sheets are placed into a filtering frame, sanitized (with boiling water, for example) and then used to filter the beer. The sheets can be flushed if the filter becomes blocked. The sheets are usually disposable and are replaced between filtration sessions. Often the sheets contain powdered filtration media to aid in filtration.

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 regeneration. Common media include [[diatomaceous earth]] and [[perlite]].

==By-products==
{{anchor|Brewer's spent grain}}
[[File:Spent grain.jpg|thumb|left|Spent grain, a brewing by-product]]

Brewing by-products are "spent grain" and the sediment (or "[[Sediment#Dregs|dregs]]") from the filtration process which may be dried and resold as "brewers dried yeast" for poultry feed,<ref>{{cite book |url=https://books.google.com/books?id=9WZ9LJLoCZIC&pg=PA79 |title=Nutrition and Feeding of Organic Poultry |author=Robert Blair |page=79 |publisher=CABI |year=2008 |access-date=8 April 2013 |isbn=9781845934286 |archive-url=https://web.archive.org/web/20160521161949/https://books.google.com/books?id=9WZ9LJLoCZIC&pg=PA79 |archive-date=21 May 2016 |url-status=live }}</ref> or made into [[yeast extract]] which is used in brands such as [[Vegemite]] and [[Marmite]].<ref>{{cite book |url=https://books.google.com/books?id=V3Sr4bbTH5oC&pg=PT174 |title=Beer: Tap into the Art and Science of Brewing |author=Charles Bamforth |page=174 |publisher=Oxford University Press |date=6 March 2009 |access-date=8 April 2013 |isbn=9780199756360 |archive-url=https://web.archive.org/web/20160515000856/https://books.google.com/books?id=V3Sr4bbTH5oC&pg=PT174 |archive-date=15 May 2016 |url-status=live }}</ref> The process of turning the yeast sediment into edible yeast extract was discovered by German scientist [[Justus von Liebig]].<ref>{{cite book |url=https://books.google.com/books?id=azXx4cbrMZMC&pg=PA58 |title=Vitamin discoveries and disasters: history, science, and controversies |author=Frances R. Frankenburg |page=58 |publisher=ABC-CLIO |year=2009 |access-date=8 April 2013 |isbn=9780313354755 |archive-url=https://web.archive.org/web/20160502233212/https://books.google.com/books?id=azXx4cbrMZMC&pg=PA58 |archive-date=2 May 2016 |url-status=live }}</ref>

[[Brewer's spent grain]] (also called spent grain, brewer's grain or draff) is the main by-product of the brewing process;<ref>{{cite book|url=https://books.google.com/books?id=uUzRBQAAQBAJ&pg=PA130|title=Advances in Food Extrusion Technology|page=130|author=Medeni Maskan, Aylin Altan|publisher=CRC Press|date=19 April 2016|isbn=9781439815212|archive-url=https://web.archive.org/web/20191226112040/https://books.google.com/books?id=uUzRBQAAQBAJ&pg=PA130|archive-date=26 December 2019|url-status=live}}</ref> it consists of the residue of malt and grain which remains in the lauter tun after the lautering process.<ref name="beldman">{{cite journal |title=Enzymatic hydrolysis of beer brewers' spent grain and the influence of pretreatments |journal=Biotechnology and Bioengineering |volume=30 |issue=5 |date=18 February 2004 |pages=668–671 |author1=G. Beldman |author2=J. Hennekam |author3=A. G. J. Voragen |pmid=18581454 |doi=10.1002/bit.260300511 |doi-access=free }}</ref> It consists primarily of grain husks, [[pericarp]], and fragments of [[endosperm]].<ref name="forssell">{{cite journal |title=Hydrolysis of Brewers' Spent Grain by Carbohydrate Degrading Enzymes |journal=Journal of the Institute of Brewing |volume=114 |issue=4 |pages=306–314 |year=2008 |doi=10.1002/j.2050-0416.2008.tb00774.x |author=Forssell Pirkko |display-authors=etal |doi-access=free }}</ref> As it mainly consists of [[carbohydrate]]s and [[protein]]s,<ref name="forssell"/> and is readily consumed by animals,<ref name="FAO"/> spent grain is used in [[animal feed]].<ref name="FAO">Heuzé V., Tran G., Sauvant D., Lebas F., 2016. Brewers grains. Feedipedia, a programme by INRA, CIRAD, AFZ and FAO. https://www.feedipedia.org/node/74 {{Webarchive|url=https://web.archive.org/web/20170824220512/https://www.feedipedia.org/node/74 |date=24 August 2017 }} Last updated on 17 June 2016, 16:10</ref> Spent grains can also be used as [[fertilizer]], whole grains in bread,<ref name="Reinhart">{{cite book |title=Peter Reinhart's Whole Grain Breads: New Techniques, Extraordinary Flavor |publisher=Ten Speed Press |date=1 September 2007 |pages=[https://archive.org/details/peterreinhartswh00rein/page/205 205–209] |author=Peter Reinhart |isbn=978-1-58008-759-9 |url=https://archive.org/details/peterreinhartswh00rein/page/205}}</ref> as well as in the production of [[flour]] and [[biogas]].<ref>{{cite book|url=https://books.google.com/books?id=P7nnCAAAQBAJ&pg=PA300|page=300|title=Poultry Feed from Waste|author=A.H. El Boushy|publisher=Springer Science & Business Media|date=17 April 2013|isbn=9789401717502|archive-url=https://web.archive.org/web/20180114020218/https://books.google.co.uk/books?id=P7nnCAAAQBAJ&pg=PA300|archive-date=14 January 2018|url-status=live}}</ref><ref>{{cite book|url=https://books.google.com/books?id=ymZkDQAAQBAJ&pg=PA232|page=232|title=Current Research Topics in Applied Microbiology and Microbial Biotechnology|author=Antonio Mendez-Vilas|publisher=World Scientific|date=2009|isbn=9789812837554|archive-url=https://web.archive.org/web/20180114021851/https://books.google.co.uk/books?id=ymZkDQAAQBAJ&pg=PA232|archive-date=14 January 2018|url-status=live}}</ref> Spent grain is also an ideal medium for growing [[Edible mushroom|mushrooms]], such as [[shiitake]], and some breweries are already either growing their own mushrooms or supplying spent grain to mushroom farms.<ref>{{cite web |url=http://www.stormbrewing.ca/STORM%20BREWING/One%20Little%20Brewery.html |title=Storm Brewing – a Canadian brewery that grows shiitake mushrooms on spent grain |publisher=Stormbrewing.ca |access-date=4 September 2013 |archive-url=https://web.archive.org/web/20130603091301/http://www.stormbrewing.ca/STORM%20BREWING/One%20Little%20Brewery.html |archive-date=3 June 2013 |url-status=live }}</ref> Spent grains can be used in the production of red bricks, to improve the open porosity and reduce thermal conductivity of the ceramic mass.<ref>Ferraz et al., Spent brewery grains for improvement of thermal insulation of ceramic bricks. Journal of Materials in Civil Engineering. [https://dx.doi.org/10.1061/(ASCE)MT.1943-5533.0000729 DOI: 10.1061/(ASCE)MT.1943-5533.0000729]</ref>

==Brewing industry==

The brewing industry is a global business, consisting of several dominant [[Multinational corporation|multinational companies]] and many thousands of other producers known as [[Craft brewery and microbrewery|microbreweries]] or regional breweries or craft breweries depending on size, region, and marketing preference.<ref name="market"/><ref>{{cite web |url=http://www.brewersassociation.org/pages/business-tools/craft-brewing-statistics/market-segments |title=Market Segments: Microbrewery |year=2012 |publisher=Brewers Association |access-date=21 June 2012 |archive-url=https://web.archive.org/web/20110718215423/http://www.brewersassociation.org/pages/business-tools/craft-brewing-statistics/market-segments |archive-date=18 July 2011 |url-status=live }}</ref> More than {{convert|133|e9L|USgal impgal|abbr=none|sp=us}} are sold per year—producing total global revenues of $294.5 billion (£147.7 billion) as of 2006.<ref name="researchandmarkets1">{{cite web|url=http://www.researchandmarkets.com/reports/53577/beer_global_industry_guide.htm|title=Beer: Global Industry Guide|publisher=Research and Markets|access-date=5 November 2007 |archive-url=https://web.archive.org/web/20071011084307/http://researchandmarkets.com/reports/53577/beer_global_industry_guide.htm |archive-date=11 October 2007 <!-- Bot retrieved archive --> |url-status=live}}</ref> [[SABMiller]] became the largest brewing company in the world when it acquired Royal Grolsch, brewer of Dutch premium beer brand [[Grolsch]].<ref>{{Cite news|url=http://archives.cnn.com/2002/BUSINESS/05/30/sab.miller/|title=Brewer to snap up Miller for $5.6B|work=CNN|date=30 May 2002|access-date=4 November 2007 |archive-url=https://web.archive.org/web/20071207043821/http://archives.cnn.com/2002/BUSINESS/05/30/sab.miller/ |archive-date=7 December 2007 <!-- Bot retrieved archive --> |url-status=live}}</ref> [[InBev]] was the second-largest beer-producing company in the world and [[Anheuser-Busch]] held the third spot, but after the acquisition of Anheuser-Busch by InBev, the new [[Anheuser-Busch InBev]] company is currently the largest brewer in the world.<ref>{{cite press release |title=InBev Completes Acquisition of Anheuser-Busch |url=http://www.ab-inbev.com/documents/press_release.pdf |publisher=AB-InBev |date=18 November 2008 |access-date=21 June 2012 |archive-url=https://web.archive.org/web/20120325102821/http://www.ab-inbev.com/documents/press_release.pdf |archive-date=25 March 2012 |url-status=dead}}</ref>

[[homebrewing|Brewing at home]] is subject to regulation and prohibition in many countries. Restrictions on homebrewing were lifted in the UK in 1963,<ref name="ukrepeal">{{cite web |url=http://www.newstatesman.com/200104090044 |title=New Statesman&nbsp;– What's your poison? |publisher=newstatesman.com |access-date=10 November 2010 |archive-url=https://web.archive.org/web/20110728155250/http://www.newstatesman.com/200104090044 |archive-date=28 July 2011 |url-status=live }}</ref> Australia followed suit in 1972,<ref name="ausrepeal">{{cite web|url=http://www.adelaidereview.com.au/_archives.php?subaction=showfull&id=1119829107&archive=1120781372&start_from=&ucat=2&|title=Adelaide Times Online|access-date=10 October 2006 |archive-url=https://web.archive.org/web/20060820163637/http://www.adelaidereview.com.au/_archives.php?subaction=showfull&id=1119829107&archive=1120781372&start_from=&ucat=2& |archive-date=20 August 2006}}</ref> and the US in 1978, though individual states were allowed to pass their own laws limiting production.<ref name="Papazian 3rd">Papazian ''The Complete Joy of Homebrewing (3rd Edition)'', {{ISBN|0-06-053105-3}}</ref>

==References==
{{reflist|30em|refs=
<ref name="market">{{cite news |url=http://biz.yahoo.com/p/bevalcmktd.html|title=Industry Browser&nbsp;— Consumer Non-Cyclical&nbsp;— Beverages (Alcoholic)&nbsp;– Company List|work=Yahoo! Finance|access-date=5 November 2007 |archive-url=https://web.archive.org/web/20071002045616/http://biz.yahoo.com/p/bevalcmktd.html |archive-date=2 October 2007 <!-- Bot retrieved archive --> |url-status=live}}</ref>
}}

;Sources
* Bamforth, Charles; ''Food, Fermentation and Micro-organisms'', [[Wiley-Blackwell]], 2005, {{ISBN|0-632-05987-7}}
* Bamforth, Charles; ''Beer: Tap into the Art and Science of Brewing'', [[Oxford University Press]], 2009
* Boulton, Christopher; ''Encyclopaedia of Brewing'', [[Wiley-Blackwell]], 2013, {{ISBN|978-1-4051-6744-4}}
* Briggs, Dennis E., et al.; ''Malting and Brewing Science'', [[Aspen Publishers]], 1982, {{ISBN|0-8342-1684-1}}
* Ensminger, Audrey; ''Foods & Nutrition Encyclopedia'', [[CRC Press]], 1994, {{ISBN|0-8493-8980-1}}
* Esslinger, Hans Michael; ''Handbook of Brewing: Processes, Technology, Markets'', [[Wiley-VCH]], 2009, {{ISBN|3-527-31674-4}}
* Hornsey, Ian Spencer; ''Brewing'', [[Royal Society of Chemistry]], 1999, {{ISBN|0-85404-568-6}}
* Hui, Yiu H.; ''Food Biotechnology'', [[Wiley-Interscience|Wiley-IEEE]], 1994, {{ISBN|0-471-18570-1}}
* Hui, Yiu H., and Smith, J. Scott; ''Food Processing: Principles and Applications'', [[Wiley-Blackwell]], 2004, {{ISBN|978-0-8138-1942-6}}
* Andrew G.H. Lea, John Raymond Piggott, John R. Piggott ; ''Fermented Beverage Production'', [[Springer Science+Business Media|Kluwer Academic/Plenum Publishers]], 2003, {{ISBN|0-306-47706-8}}
* McFarland, Ben; ''World's Best Beers'', [[Sterling Publishing]], 2009, {{ISBN|978-1-4027-6694-7}}
* [[Garrett Oliver|Oliver, Garrett]] (ed); ''The Oxford Companion to Beer'', Oxford University Press, 2011
* Priest, Fergus G.; ''Handbook of Brewing'', [[CRC Press]], 2006, {{ISBN|0-8247-2657-X}}
* {{cite book |last1=Rabin |first1=Dan |first2=Carl |last2=Forget |title=The Dictionary of Beer and Brewing |location=Chicago |publisher=Fitzroy Dearborn/[[Taylor & Francis]] |year=1998 |type=Print |isbn=978-1-57958-078-0}}
* Stevens, Roger, et al.; ''Brewing: Science and Practice'', [[Woodhead Publishing]], 2004, {{ISBN|0-8493-2547-1}}
* Unger, Richard W.; ''Beer in the Middle Ages and the Renaissance'', [[University of Pennsylvania Press]], 2004, {{ISBN|0-8122-3795-1}}

==External links==
{{Portal|Beer}}
{{Commons category|Brewing}}
* {{cite EB9 |wstitle = Brewing |volume= IV | pages=264-275 |short=1}}
* [http://www.scq.ubc.ca/?p=345 An overview of the microbiology behind beer brewing from the Science Creative Quarterly]
* [http://www.inwithbacchus.com/2010/10/in-with-bacchus-guide-collegiate.html A pictorial overview of the brewing process at the Heriot-Watt University Pilot Brewery]

{{Alcoholic beverages}}

{{Authority control}}

[[Category:Brewing| ]]
[[Category:Fermentation in food processing]]