A type of evaporator used for concentrating heat-labile solutions. It consists of a vertical cylindrical column or cylinder surrounded by a steam jacket. The solution to be evaporated enters the top of the vessel and is allowed to descend the inner walls under the influence of gravity. A rotating assembly of blades with a close clearance to the wall ensures a short hold-up and corresponding residence time, where longer residence times at the boiling temperature would otherwise damage the solution.