In a pub, beer is typically thought of as coming out of a barrel but that’s not always true.
At the brewery beer is put into containers called casks not barrels. Evan though the cask is barrel shaped, it is the quantity of liquid, in gallons, that one of these casks holds which will determine its name,(but there is a cask called a barrel).
So what are the cask sizes? There are seven sizes normally referred to:
Pin or Polypin 4.5 gallons
Firkin 9 gallons
Kilderkin 18 gallons
Barrel 36 gallons
Hogshead 54 gallons
Butt 108 gallons
Tun 216 gallons
These names are thought to date back to 1454.
Beer is usually delivered to pubs in Firkins or Kilderkins, which are thought to be the most convenient for sales purposes and easiest to handle. Now having said all this, when the beer starts to splutter and run out as it’s being poured the pub staff always confusingly go and ‘Change the barrel’.