Editing Brewing (section)

===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>