is a small wooden
fitting used in ale casks
For some years wooden casks have been effectively obsolete, with the majority now being aluminium
or stainless steel
, and a few sturdy plastic ones beginning to appear. Nevertheless, the standard tap
is still designed to be hammered into yielding material, punching a hole as it goes. All modern casks, even the few wooden ones still in use, use a replaceable keystone to accept the tap.
The bung-hole of the cask is on one of the circular faces, near the rim. When the cask is in service, it is laid on its side with the bunghole at the lowest point on the circumference. The keystone is a small thick wooden or plastic disk inserted into the bunghole which completely seals the cask until it is needed.
The centre of the keystone is deliberately weakened. In the plastic variety it is much thinner than the surrounding material; if made of wood it is partially pre-cut so that it is easier to punch out. Some time before the cask is to be served, the end of the tap is placed against this weakened section and, with the aid of a mallet
, driven through it. The shaft of the tap is tapered, so that as it is forced in fully it seals against the undisturbed outer part of the keystone. A small amount of beer may leak out during this process, but with sufficient skill and firm action with the mallet, no spillage at all can occur.
When the cask is empty, it is a courtesy to the drayman (the brewery's delivery driver who also collects... Read More