Originally, the coaster was placed on top of the Kölsch glass to keep anything from falling into the beer and to help it stay fresh for longer. Over time, this simple idea became a Cologne tradition that is still part of brewhouse and pub culture today. Every Kölsch you drink is marked with a line on your coaster. 

That way, both you and the Köbes can keep track of how many glasses have been served. And that matters, because in a Cologne brewhouse you do not usually order your next beer. As soon as your glass is empty, the Köbes brings you another freshly tapped Kölsch. There is only one way to make it stop: put your coaster on top of the glass. That simple sign tells the Köbes you have had enough. Or, as we say in Cologne: “Der hät keine Doosch mih.” A small ritual, but one that belongs to Cologne brewhouse culture just as much as the Kölsch itself.