A beer keg is a container used to store and dispense beer. Typically made of stainless steel, kegs come in various sizes, with the most common being the half-barrel, which holds about 15.5 gallons. Kegs are designed to maintain the beer's carbonation and freshness, making them ideal for bars, restaurants, and parties. Kegs are often connected to a keg tap or draft system that allows for easy pouring. When tapped, the beer is pushed out by either gravity or gas pressure, usually from carbon dioxide or nitrogen. This method of serving beer is popular for its efficiency and ability to serve large quantities at once.