A cask breather (sometimes called a cask aspirator) is a type of demand valve used to serve draught beer.
The cask breather enables the empty space created when beer is drawn from a beer cask to be filled with carbon dioxide from an external source.
[1] To avoid carbonation of the beer, the carbon dioxide gas added by a cask breather is at low pressure, unlike the high pressure gas used to pressurize keg beer.
[citation needed] Before 2018, the use of cask breathers was opposed by the Campaign for Real Ale (CAMRA),[2] a policy that was changed in April 2018 to allow pubs using cask breathers to be classified as real ale pubs and listed in the Good Beer Guide.
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