Brewers' ovens, also known as oasts, are used in the brewing process to dry hops. They are typically cylindrical in shape and have a rotating internal rack that allows for even drying of the hops. The heat is usually provided by a wood or coal fire, and the smoke is often vented through a tall chimney. Oasts are an essential part of the brewing process, as they help to bring out the flavor and aroma of the hops.