A method for heating a sugar solution, characterised in that the solution is caused to flow along a tubular passage (66) surrounding a heated central tube (64), the tubular passage (66) being surrounded by an outer tube (24), the flow is forced around a plurality of diverters (70) which extend substantially across the passage (66), each of which diverters (70) deflects the solution from the major flowpath determined by the tubular passage (66), to induce eddies or small cross-currents in the solution flow, thereby to enhance the mixing of the solution and/or the heat transfer to the solution.