Ask the expert – cask breathers

Since 2018, CAMRA has adopted a neutral stance on the use of cask breathers, neither encouraging nor 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 one pint of gas for every pint of beer drawn off, preventing oxygen being drawn in. Any additi......