A method for producing metal castings comprising the steps of: i) providing a conditioning furnace, having an inlet channel and an outlet channel, with pre-treated molten metal; and ii) reducing the height of molten metal in the outlet channel to a level (h1) lower than the level of the molten metal in the conditioning furnace (h0) such that the molten metal in the spout and in the outlet channel, at least partly, is brought back into the furnace body where it can be recharged with a nucleating and/or structure modifying agent, iii) adding further nucleating and/or structure modifying agent to the molten metal when necessary, iv) mixing the melt in the furnace when necessary and v) after the stoppage, casting the melt with the desired content of structure modifying agent.