The invention relates to a microwave oven comprising a cooking chamber in which food to be heated can be placed, a microwave generator for radiating microwave energy into said chamber to heat said food, fan means for producing an air flow to cool the generator and for directing air into said chamber, and humidity sensor means positioned in a sensor compartment downstream the cooking chamber after leaving said food to sense a change in humidity of the air in said chamber, said cooking chamber having a plurality of inlet apertures and an outlet opening communicating with said sensor compartment.
A known microwave oven of this type is described in U.S. Pat. No. 4,587,393. In this oven, the humidity emitted by the food encounters the humidity sensor together with all the cooling air. The sensed humidity can be used as an indication of the condition of the food. For equal conditions, the quantity of humidity emitted by a food product is related to its free evaporation surface area. The result is that as the cooling air flow is constant, a smaller free evaporation area leads to a greater dilution of the water vapour evolved by the food, the response of the humidity sensor thus occurring when the food has reached a temperature higher than required. Because of this fact, the use of this known method can result in differences of about 30.degree. C. with respect to the required temperature set by the user.