Since 2018, CAMRA has adopted a neutral stance on the use of cask breathers, neither encouraging or objecting to their use.

A cask breather, also known as a demand valve or cask aspirator, is a relatively simple automatic device which applies carbon dioxide (or another neutral gas) at exactly atmospheric pressure. As beer is drawn from a cask, it tops up the space above the beer with exactly the same amount removed, preventing oxygen being drawn in. Any additional CO2 generated by secondary fermentation in the cask is automatically vented to the atmosphere.

Prior to 2018, CAMRA acknowledged cask breathers could play a useful role in maintaining good cask beer in limited circumstances, most notably pubs or clubs with marginal or erratic turnover. However, for general use, CAMRA was concerned the presence of breathers could encourage publicans to stock a larger range of cask beers or in larger sizes than their sales justified, keeping them on sale longer than the brewers ever intended, affecting the quality being served. 

Taste trials carried out on behalf of CAMRA’s Technical Advisory Group demonstrated that with a fresh beer, a very small minority of drinkers could detect the difference between a cask ale served under a breather and one vented direct to the atmosphere. However, while cask breathers slow down oxidation (which causes stale cardboard or sherry flavours in beer) and prevent bacterial infection from the atmosphere, they do nothing to limit the other spoilage mechanisms which can introduce more subtle off flavours in cask ale. They can therefore lead to beers being kept on sale long past their prime.

CAMRA believes cask breathers are not necessary in outlets with a sensible number of ales and normal sales patterns. If publicans are finding beers are on sale too long, publicans should moderate their range or use smaller cask sizes to only stock the volume and number they can realistically sell within three days.

John O’Donnell (pictured) is a member of CAMRA's Technical Advisory Group, a Great British Beer Festival bar manager and editor of Beer Buzz.

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