Glossary · Equipment
Keystone
Definition
The small plug set into the end of a cask, through which a tap is driven when the cask is put on to serve.
- Subject
- Equipment
In more detail
The keystone is one of two soft plugs a cask carries, and the pair is worth understanding together because they do opposite jobs. The shive sits in the bung hole on the belly of the cask and is where the cask is filled and vented; the keystone sits in the end and is where the cask is tapped. Both are traditionally beech or, now, a food-grade plastic, and both are designed to be driven through rather than removed.
Driving the tap through the keystone rather than unscrewing anything is the point of the design: the cask stays sealed until the moment it is put on to serve, and the seal is made by the same wood the tap has just displaced. A tap driven cleanly and squarely does not leak; one driven at an angle does, and there is no second attempt.
Related terms
Terms that belong to the same part of the subject, or that this one is routinely confused with.
Equipment
Shive
The wooden or plastic plug driven into the bung hole on the belly of a cask, carrying a smaller central section through which a spile can be pushed to vent gas.
Equipment
Spile
A small peg driven into the shive to control the escape of carbon dioxide from a cask. A porous soft spile lets gas vent; a hard spile seals the cask to retain condition.
Equipment
Cask
A wooden vessel of staves bound by hoops, bulging at the middle so it can be rolled and turned. Casks both store cider and shape it, admitting a slow ingress of oxygen through the wood.
Serving
Gravity dispense
Serving cider from a tap in the cask or box by gravity alone, without pump or applied gas. It is the traditional method for still farmhouse cider and the standard at cider festivals.
Where to go next
- Cider glossary — The whole vocabulary, by subject and A–Z.
- Comparisons — Terms that are only really clear when set against the thing they are not.
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Sources
What this page rests on. Where a source is marked as registered rather than read, CiderHQ is recording that the body is authoritative on the subject without claiming to have worked through the document itself. See our evidence policy for what each state means.
CAMRA cider and perry standards
Campaign for Real Ale · specialist organisation · retrieved 2026-08-24
Opened on 2026-08-24. Registered for the consumer-campaigning vocabulary — "real cider", "full juice" — which is advocacy language rather than legal definition, and is recorded as such wherever CiderHQ uses it.