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 dire ...

. 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 stave (wood), staves and bound by wooden or metal hoops. The word vat is often used for large containers f ...

to be filled with

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

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, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

. 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 ch ...

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. Cask breathers are typically used in conjunction with a

pressure regulator A pressure regulator is a valve that controls the pressure of a fluid or gas 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 setti ...

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, England, which promotes real ale, cider and perry and traditional British pubs and clubs. With just under 155,000 members, it is th ...

(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 beer 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 car ...

pubs and listed in the '' Good Beer Guide''.

References

See also