In roller drying the product is distributed on rotating, steam-heated drums. The water in the product evaporates and is drawn off by a flow of air when it comes in contact with the hot drum surface.
The pretreated product is admitted to a trough formed by the cast iron drums and their end walls. A thin layer of product on the drums is heated quickly when it comes in contact with the hot surface. The water is evaporated and the layer of product on the drum dries. This film is continuously scraped off by knives in contact with the periphery of each drum.
The dried product falls into a screw conveyor in which it is ground into flakes. The flakes are then transferred to a grinder, and hard and burned particles are separated on a screen at the same time.