wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...
en or
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
casks
A barrel or cask is a hollow cylindrical container with a bulging center, longer than it is wide. They are traditionally made of wooden staves and bound by wooden or metal hoops. The word vat is often used for large containers for liquids, u ...
. It is found on the curved side of the cask, arranged so that when the cask is on its side and the keystone is at the lowest part of the rim, the shive will be the highest point of the cask.
The hole in that part of the cask is used for two purposes. Firstly, it is used for cleaning out and then refilling the cask, which requires a large hole. Once the cask arrives at its destination, the hole is used to control the amount of
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
present in the container, which requires a small hole. The shive is effectively an adaptor that reconciles these conflicting requirements. It is a wooden disk, larger than a keystone, that fits in the hole in the cask and has a smaller hole in its centre.
For washing and filling, the old shive is removed using a chisel or a special tool, revealing a hole around 3 inches (7.5 cm) across. Once the cask has been filled and fined, a new shive is hammered into place. The hole in the centre of the shive will be sealed with a small wooden or plastic peg. The cask is then transported to the
pub
A pub (short for public house) is a kind of drinking establishment which is licensed to serve alcoholic drinks for consumption on the premises. The term ''public house'' first appeared in the United Kingdom in late 17th century, and was ...
.
Some time before the beer is to be served (two or three days is common; especially strong beers may require more) the cask is opened or "vented". This entails breaking the seal in the middle of the shive by punching it through into the cask with a mallet and some kind of tool, usually just a hard spile.
A spile is then placed in the hole to regulate the gas flow. If the beer is particularly "lively" (common in warm weather and with specific beers) the contents may spray out when the cask is vented.
During use, the hole in the centre of the shive can also be used (with the spile removed) to insert a marked
dipstick
A dipstick is one of several measurement devices.
Some dipsticks are dipped into a liquid to perform a chemical test or to provide a measure of quantity of the liquid.
Since the late 20th century, a flatness/levelness measuring device trademarke ...
in order to measure the quantity of beer remaining.
As with keystones, it is considered good form to close up the hole in the shive when returning empty casks, both to prevent spillage and to reduce bacterial and fungal contamination.