An apparatus for the heat treatment of a product, especially a food product such as a food product contained within a hermetically sealed container or pouch of plastics or like material, for example for sterilization, pasteurization or cooking, having a heating unit to bring product from ambient towards a heat treatment temperature and pressure; a retort unit to apply a heat treatment to a product; and a cooling unit to allow product to be brought down from heat treatment temperature and pressure towards ambient; wherein each unit and retort is selectably sealable from the others and from ambient conditions.