and brewery to brewery with most countries using the metric system rather than U.S. gallons. A keg, or half-barrel is a 15.5 U.S. gallon vessel. A quarter-barrel has a volume of 7.75 U.S. gallons. Generally a keg is a vessel smaller than a barrel; thus, it is 30 gallons or smaller. In the U.S. the terms half-barrel and quarter-barrel are derived from the U.S. beer barrel, legally defined as being equal to 31 U.S. gallons (this is not the same volume as some other units also known as barrels). A 15.5 U.S. gallon keg is also equal to: 12.7 Imperial gallons 58.67 liters 103.25 Imperial pints 124 U.S. pints 496 U.S. gills 165 twelve fluid ounce (U.S. measure) drinks About 90 bombers (22 fl oz bottles) About 6.88 24-unit cases of 12 fl oz cans About 5.5 30-racks of 12 fl oz cans 1,984 fluid ounces (U.S.) However, beer kegs can come in many sizes: Specifications for a U.S. barrel keg Accepted specifications for a standard keg are: DIN-keg and Euro-keg In Europe, the most common keg size is 50 liters. This includes the UK, which uses a non-metric standard keg of 11 imperial gallons, which is, by coincidence, equal to . The German DIN 6647-1 and DIN 6647-2 have also defined kegs in the sizes of 30 and 20 liters. In some areas it is common to refer to the size not in liters but in beers. In areas such as Germany, where the standard beer size is 0.5 liters, that means a 50-liter keg contains 100 beers. Taps Kegs are sealed to contain the liquid and pressurized gas for storage and transportation. Most beer is served carbonated, and this is most easily accomplished by storing it carbonated as well. Beer kegs are designed to maintain the carbonation in a beverage by storing it with pressurized carbon dioxide in the headspace above the liquid. The liquid is also dispensed using pressurized gas; the pressure of the gas provides mechanical force to overcome friction and gravity to push the beer to the dispensing location. To serve the beverage, a keg must be tapped to breach the container so that pressurized gas can be added and the liquid can be dispensed. Originally, this was done by hammering a tapping rod through a cork bung, similar to how a keystone is still used today to tap unpressurized cask ales. Tapping a keg