keg

A keg is a pressurized vessel used to store and dispense beverages, most notably beer. It is typically a metal cylinder made from stainless steel or aluminum, with a sanitary interior finish to resist corrosion and prevent contamination. Kegs are designed to withstand internal pressure from carbon dioxide or CO2-nitrogen gas blends used in draft systems, and they include fittings and valves that allow gas to pressurize and beer to be drawn through a tap.

Common sizes in commercial use include the 1/2 barrel (15.5 gallons or about 58.7 liters), the 1/4 barrel (7.75 gallons or about 29.3 liters), and the 1/6 barrel (5.16 gallons or about 19.5 liters). A 5-gallon Cornelius keg is widely used by homebrewers. In some markets, sizes are specified in liters. Kegs may use different coupler types, such as ball-lock or pin-lock connections for beer lines, and require a gas coupler or regulator to maintain the dispensing pressure.

Operation typically involves filling the keg with beer, sealing it, and charging it with a regulated gas supply. The gas pressure pushes beer to the tap, where it is dispensed through a beer line and faucet. Regulators help maintain standard dispensing pressures, often in the range of 10–14 psi for many ales and lagers, with variations depending on beer style and system design. A relief valve helps prevent overpressure, and proper cleaning and sanitation are essential to maintain quality and safety.

History and use: kegs helped standardize beer transport and draft service, replacing wooden barrels in many contexts and becoming central to bars, restaurants, and homebrewing alike.