Keg, a pressurized container for packaging, transporting, and dispensing carbonated draught beer. Although kegs have been made out of many materials over time, including wood, plastic, and aluminum, the vast majority are now made from stainless steel. The standard beer keg, which once featured curved walls that mimicked barrel staves, is now a straight-side cylindrical container. Above the walls is a rounded rim with hand grips, sometimes coated in rubber, called the chime. In the neck at the top of the container is a spring-loaded valve connected to a drop-tube called a spear. The spear reaches to within a centimeter of the bottom of the keg, allowing almost all the contents of the keg to be served out.
Most types of kegs use a single coupler; this allows gas pressure to enter the keg, forcing beer to leave the keg via the spear. The most common modern keg coupler design is known by the name Sankey, although there is an American variation and a European one; at first glance these appear to be interchangeable, but they are not. Beyond these there are several other coupler designs in use, including the Bass Grundy “G” coupler, still used in the UK, and the German “A” and “M” couplers, all of which slide onto the keg neck rather than twisting on as the Sankey types do.
Two older systems are still occasionally seen—Hoff–Stevens and Golden Gate. Both were unwieldy because of their wooden bungs, which required replacement after each use, and the Golden Gate keg had a gas fitting that was separate from the beer fitting.
Kegs are generally cleaned and filled in an inverted position on a keg cleaning and filling machine. The machine first blows out any remaining beer in the keg and then takes the keg through a rinse, cleaning by hot caustic soda and sometimes acid, another rinse, and steam or chemical sterilization, and then the keg is pressurized and filled.
The standard American keg volume is the American half-barrel, which is 58.6 l or 15.5 US gal. Most European kegs are notably smaller, at 50 l, with many available at 30 and 20 l, sizes that better comply with European labor laws regarding workplace ergonomics. American kegs also come in a range of sizes, with the second most common size being 5 US gal.