A device and a method are provided for measuring the moisture in die cast molds, the cavity of which is connected via an evacuation conduit to an evacuation device. The modular assembly of the device is connectable to the evacuation conduit and includes a sensor assembly to measure the moisture of gases evacuated from the mold cavity. The sensor assembly includes an emitter emitting electromagnetic radiation and a detector detecting electromagnetic radiation. On the basis of the measured values obtained during the evacuation action it can be determined whether the amount of a water/release agent mixture jetted into the mold cavity needs to be altered before the actual casting action.