An OAST is a type of tobacco-drying oven used in the production of tobacco. It is typically a tall, cylindrical structure with a conical or pyramidal roof, and has openings at the base and top to allow air to circulate. The heated air from the bottom of the OAST is used to dry the tobacco leaves, which are hung from the rafters inside the structure. The OAST is an important part of the tobacco-making process, as it helps to reduce the moisture content of the leaves and improve their flavor.