Editing Draught beer (section)

== Keg beer ==
[[File:Beer Keg outside the Plasterers Arms, Hoylake.JPG|upright|thumb|A typical {{convert|11|impgal|L|adj=on|order=flip}} keg with single opening in the centre of the top end]]
Keg beer is often [[filtration|filtered]] and/or [[pasteurization|pasteurised]], both of which are processes that render the [[yeast]] inactive.<ref>{{Cite web|title=What is The Beer Pasteurization Process?|url=https://www.micromatic.com/beer-pasteurization|access-date=2021-04-30|website=micromatic.com}}</ref><ref>{{Cite web |last=universitydrafthouseadmin |date=2023-03-27 |title=The Benefits of Draft Beer |url=https://universitydrafthouse.com/2023/03/27/the-benefits-of-draft-beer/ |access-date=2024-01-15 |website=University Draft House |language=en-US}}</ref>

In brewing parlance, a keg is different from a [[cask]]. A cask has a tap hole near the edge of the top, and a [[spile]] hole on the side used for conditioning the unfiltered and unpasteurised beer. A keg has a single opening in the centre of the top to which a flow pipe is attached. Kegs are artificially pressurised after [[Brewing#Fermenting|fermentation]] with [[carbon dioxide]] or a mixture of carbon dioxide and [[nitrogen]] gas or especially in [[Czech Republic]] solely [[compressed air]].

''Keg'' has become a term of contempt used by some, particularly in the UK, since the 1960s when pasteurised draught beers started replacing traditional cask beers.

Keg beer was replacing traditional cask ale in all parts of the UK, primarily because it requires less care to handle. Since 1971, CAMRA has conducted a consumer campaign on behalf of those who prefer traditional cask beer. CAMRA has lobbied the [[British Parliament]] to ensure support for [[cask ale]] and [[microbrewery|microbreweries]] have sprung up to serve those consumers who prefer traditional cask beer.

Pressurised CO<sub>2</sub> in the keg's headspace maintains carbonation in the beer. The CO<sub>2</sub> pressure varies depending on the amount of CO<sub>2</sub> already in the beer and the keg storage temperature. Occasionally the CO<sub>2</sub> gas is blended with nitrogen gas. CO<sub>2</sub> / nitrogen blends are used to allow a higher operating pressure in complex dispensing systems.

Nitrogen is used under high pressure when dispensing dry [[Stout beer|stouts]] (such as [[Guinness]]) and other creamy beers because it displaces CO<sub>2</sub> to (artificially) form a rich tight [[Head (beer)|head]] and a less carbonated taste. This makes the beer feel smooth on the palate and gives a foamy appearance. Premixed bottled gas for creamy beers is usually 75% nitrogen and 25% CO<sub>2</sub>.<ref>{{Cite web|url = http://www.lbbrew.com/beer-on-nitro/|title = Beer on Nitro|last = Burns|date = 6 July 2013|first = David|website = Lake Bluff Brewing Company|url-status = dead|archive-url = https://web.archive.org/web/20131004232043/http://www.lbbrew.com/beer-on-nitro/|archive-date = 4 October 2013}}</ref> This premixed gas, which only works well with creamy beers, is often referred to as Guinness Gas, Beer Gas, or Aligal (an Air Liquide brand name). Using "Beer Gas" with other [[beer style]]s can cause the last 5% to 10% of the beer in each keg to taste very flat and lifeless. In the UK, the term ''keg beer'' would imply the beer is pasteurised, in contrast to unpasteurised cask ale. Some of the newer microbreweries may offer a nitro keg stout which is filtered but not pasteurised.