English brewery cask units
Capacities of brewery casks were formerly measured and standardised according to a specific system of English units, which was originally based on the ale gallon of exactly .
With the adoption of the imperial system in the United Kingdom and its colonies in 1824, these 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 beer tun is equal to double the size of a butt: it is therefore exactly or approximately. This unit is exactly larger than the English [wine cask units#Tun|wine tun].Butt (Imperial)
The butt of beer is equal to half a tun or two hogsheads, and is therefore exactly or approximately. This unit is exactly larger than the wine pipe or butt.Puncheon
The puncheon of beer is equal to of a tun, of a butt or hogsheads, and is therefore exactly or approximately. This unit is exactly larger than the wine puncheon.Hogshead
The hogshead of beer and ale is equal to a quarter of a tun, half a butt, or three kilderkins. This unit is exactly larger than the wine hogshead.Barrel
The barrel of beer or ale is equal to two kilderkins or of a beer or ale hogshead. This unit is exactly larger than the wine barrel, and is also exactly larger than the wine tierce.Kilderkin
The kilderkin is equal to half a barrel or two firkins.This unit is exactly larger than a wine kilderkin, and is also exactly 20% larger than a rundlet.
The kilderkin 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, while 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.Casks in this size are the most common container for cask ale.
This unit is exactly larger than a wine firkin, though firkin was also used as a name for the much larger wine puncheon.
Most English cask conditioned beer bought by publicans is delivered in 72 pint containers, but the volume of consumable beer in the container is far lower. For example a 72 pint container of Greene King IPA currently only has 66 "full" pints of consumable beer that can be sold or drunk: the other 6 pints are sediment, finings, beer stone, hops, proteins or less than an imperial measure and therefore not consumable or saleable. HMRC does not charge duty on any portion of beer that cannot be consumed, and brewers should make a declaration to the first customer to inform them what are the actual duty paid contents of the beer so customers are fully aware of how much is being sold to them.
Pin (Imperial)
A pin is equal to half a firkin, and is therefore exactly or approximately.This unit is exactly larger than a wine pin.
Plastic versions of these casks are known as "polypins" and are popular in homebrewing, the off-trade, and at beer festivals where non-standard beers are sold.