A temperature of a metal melt in a furnace is maintained after blowing away slag from a surface of the metal melt by the flow of oxygen and switching over from oxygen to an inert gas, such as nitrogen. A measured temperature of the metal melt is accepted as a metal melt temperature only when the inert gas flow is in a laminar state and after the measured temperature has fluctuated by a maximum of 1% over a period of at least 2 seconds.