Abstract: Batch and continuous fluid processing devices including means for generating toroidal flow in a fluid to be processed, disposed in a container whose internal surface conformation corresponds to and is substantially defined by the external surface of the fluid when it is undergoing toroidal flow. In preferred forms, processing apparatus includes a blade mounted for axial rotation within a vessel having bowl shaped interior. The vessel is provided with a lid whose interior surface is shaped to conform to the upper surface of a fluid undergoing toroidal flow.