Methods for treating aluminum in a furnace. An aluminum charge is introduced into a furnace and melted with heat from at least one burner. The burner is supplied with at least one oxidizer and at least one fuel. The oxidizer is made up of at least 10% oxygen by volume. The concentration of a first gas is measured in the furnace atmosphere or in a flue gas exiting the furnace. The oxidation of the molten aluminum is then reduced by holding the flow rate of the oxidizer steady while varying the flow rate of the fuel, according to the concentration of a second gas in the furnace or in the flue gas exiting the furnace. The concentration of the second gas is determined by comparing the measured species concentration and the intrinsic concentration which would be present absent the aluminum charge.