During cooling, water is constantly circulated through the retort in the same way as during water processing. Cooling water flows in countercurrent through a heat-exchanger to indirectly cool the process water inside the retort. Heat-exchanger cooling is recommended if the main criteria is water efficiency, provided that the retors is connected to a closed-circuit cooling plant. Also, the mass of cooling water never directly touches the product, allowing for more cos-effective treatment of the process water.