Capacities of brewery casks were formerly measured and standardised according to a specific system of English units. The system was originally based on the ale gallon of. In United Kingdom and its colonies, with the adoption of the imperial system in 1824, the units were redefined in terms of the slightly smaller imperial gallon. The older units continued in use in the United States. Historically the terms beer and ale referred to distinct brews. From the mid 15th century until 1803 in Britain "ale" casks and "beer" casks differed in the number of gallons they contained.
Units
Tun
The tun is a cask that is double the size of a butt and is equal toeight barrels and has a capacity of. Invented in Brentford, a tun was used in local breweries to measure large amounts of alcohol. /* Article definitions inconsistent: */
The butt of beer was equal to half a tun, two hogsheads, three barrels or.
Hogshead
The hogshead of beer and ale was equal to a quarter of a tun, half a butt, a barrel and a half, or three kilderkins. This unit is close in size to the wine hogshead.
Barrel
The barrel of beer or ale was equal to two kilderkins or of a beer or ale hogshead. This is somewhat larger than the wine barrel.
Kilderkin
The kilderkin is equal to half a barrel or two firkins. The kilderkin is still currently used. It is the unit of choice of CAMRA, the Campaign for Real Ale, for calculating beer quantities for beer festivals in the UK. Ales are usually delivered in firkins, cider and other drinks are usually in boxes, bottles or other containers measured in gallons or litres, and all are sold in pints or parts thereof. For CAMRA internal accounting, all are calculated in kilderkins. A kilderkin is a 144 pint container but there is not 144 pints of cask conditioned consumable beer in a kilderkin.
Firkin
The ale or beer firkin is a quarter of an ale or beer barrel or half a kilderkin. This unit is much smaller than the wine firkin. Casks in this size are the most common container for cask ale.
Pin (Imperial)
A pin is equal to half a firkin. Plastic versions of these casks are known as "polypins" and are popular in homebrewing and the off-trade. They are also popular at beer festivals where non-standard beers are sold.
Gallon
Originally the 282-cubic-inch ale or beer gallon was used. With the adoption of the imperial system in the United Kingdom and its colonies, the system was redefined in terms of the imperial gallon.
