Cask breather

What is actually happening

A cask works because air replaces the beer as it is drawn. That is also what kills it: oxygen begins staling the beer immediately, which is why a broached cask has a few days rather than a few weeks.

A breather is a demand valve. It admits carbon dioxide at atmospheric pressure only as beer leaves, so the headspace fills with inert gas rather than air. It does not push the beer, and it does not carbonate it — the pressure is the same as the room.

The argument about it is genuine and unresolved. It extends a cask’s life several days and reduces waste; it also alters the slow oxidative change that some drinkers consider part of what cask ale is. The relevant trade body has permitted it under conditions rather than settling the question.

BeerHQ records the mechanism and the dispute, and takes no position on whether a breathered cask is still cask ale — that is a definitional argument rather than a technical one.

What goes wrong here

Risks rather than certainties. This step does not cause these faults; getting it wrong can.

• Oxidation — The universal ageing fault: oxygen degrades beer into papery, cardboard-like staleness, and dulls everything that made it good.

Related steps and concepts

• Cask conditioning — The system it modifies.
• Nitrogenation — A different gas used for a different purpose.