An apparatus detects changes in water vapor above a cooktop surface and includes a radiation source that is positioned below the cooktop surface. The radiation source emits radiation having a predetermined water vapor absorption wavelength. A beam splitter splits the emitted radiation into a first radiation beam and a second radiation beam. The first radiation beam is directed through and above the cooktop surface. A reflective surface positioned above the cooktop surface reflects the first radiation beam. A radiation sensor detects the reflected first radiation beam and generates a sensor output. A reference radiation sensor receives the second radiation beam from the beam splitter and generates a reference output. A processor is connected to the radiation sensor and the reference radiation sensor and receives the sensor output and the reference output. Changes in water vapor above the cooktop surface are determined by analyzing the sensor output and the reference output.