The present invention refers to a method of detecting the moisture in an apparatus for treating and preparing food, as well as to a method of treating and preparing food. In the method according to the invention, the current temperature values and speed values of the asynchronous motor driving a gas supply and circulation mechanism are compared to at least one characteristic line which is stored in a computer, and the current moisture in the gas mixture is determined from the deviation N of the measured speed from the speed of the stored characteristic line. The present invention also comprises an apparatus for treating and preparing food that, in particular, serves to carry out the method of determining the moisture in a gas mixture.