An oven includes: an inlet elevator having multiple receiving bays for receiving a piece to be heated in the oven where the receiving bays are stacked vertically and the elevator is configured to move up or down to align a receiving bay; a mandrel having multiple shelves to correspond a shelf to a bay of the inlet elevator, each shelf configured to support a piece received from the inlet elevator, the mandrel configured to rotate each piece on a shelf between a loading position, a baking position, and an unloading position; an outlet elevator having multiple receiving bays for unloading a piece heated in the oven, the unloading bays are stacked vertically and the elevator is configured to move up or down to align an unloading bay with a material handling system moving the heated pieces; and a microwave generator configured to heat at least one of the pieces when the pieces are in the baking position. A method of heating a material is also provided.