Hops-drying kilns, also known as oasts, are structures used in the brewing process to dry hops. They are typically cylindrical in shape and have a conical roof with a rotating cowl at the top. The cowl is used to draw off the hot air created by the kiln, which is then used to dry the hops. The hops are placed in a mesh basket inside the kiln, and the heat from the fire is circulated around the basket to dry the hops. The dried hops are then used to flavor beer.