A cask breather (sometimes called a cask aspirator) is a type of demand valve used to serve

draught beer Draught beer, also spelt draft, is beer served from a cask or keg rather than from a bottle or can. Draught beer served from a pressurised keg is also known as Name Until Joseph Bramah patented the beer engine in 1785, beer was served ...

. The cask breather enables the empty space created when beer is drawn from a

beer cask A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, ...

to be filled with

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

from an external source. This prevents ambient air from being drawn into the cask, thus extending the life of the beer by preventing

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

. To avoid

carbonation Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids. In inorganic che ...

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 Draught beer, also spelt draft, is beer served from a cask or keg rather than from a bottle or can. Draught beer served from a pressurised keg is also known as Name Until Joseph Bramah patented the beer engine in 1785, beer was serv ...

. Cask breathers are typically used in conjunction with a

pressure regulator A pressure regulator is a valve that controls the pressure of a fluid to a desired value, using negative feedback from the controlled pressure. Regulators are used for gases and liquids, and can be an integral device with a pressure setting, a r ...

to ensure the gas pressure is sufficiently low. Before 2018, the use of cask breathers was opposed by the

Campaign for Real Ale The Campaign for Real Ale (CAMRA) is an independent voluntary consumer organisation headquartered in St Albans, which promotes real ale, cider and perry and traditional British pubs and clubs. History The organisation was founded on 16 ...

(CAMRA), a policy that was changed in April 2018 to allow pubs using cask breathers to be classified as

real ale Real ale is the name coined by the Campaign for Real Ale (CAMRA) for ale that is "brewed from traditional ingredients, matured by secondary fermentation in the container from which it is dispensed, and served without the use of extraneous ca ...

pubs and listed in the ''

Good Beer Guide The ''Good Beer Guide'' is a book published annually by the Campaign for Real Ale (CAMRA), listing what it considers to be the best 4,500 real ale outlets (pubs, clubs, and off-licences) in the United Kingdom. Details The content of the ''Guid ...

''.

References

See also