A keg coupler is a device used to connect a keg of beer to a draft beer system. It allows for the flow of beer from the keg to the tap, enabling the beer to be served. Keg couplers come in various types, each designed for specific keg styles, such as D System for most American beers or S System for European beers. The coupler works by puncturing the keg's seal and creating a pathway for the beer to flow. It also allows for the introduction of gas, typically carbon dioxide, to push the beer out of the keg. Proper use and maintenance of keg couplers are essential for ensuring the quality and freshness of the beer served.