Abstract: Products having at least an outer layer of a hot semi-liquid material which crystallizes and hardens upon cooling are placed on a conveyor and transported through a cooling tunnel. Within the cooling tunnel, the product is initially subjected to a high voltage field producing a corona current to accelerate initial cooling. The product is moved out of the field while the surface is still semi-liquid and subjected only to the cool air environment of the tunnel while the surface crystallizes and hardens. The product is then moved into a second high voltage field producing a corona current to remove heat from the inner regions of the material to inhibit remelting of the surface after the product exits the cooling tunnel.