A fryer (100) generates electromagnetic waves between a pair of opposing flat plate antennas (102) to control water as a component in food, specifically the water activity of an object. The fryer (100) irradiates the food with the electromagnetic waves of a frequency of 50 kHz by applying, to an alternating-current electric field and as an offset electric field, a direct-current electric field of +100V on the water phase side with respect to oil phase. In this way, the interface polarization between water phase and oil phase is increased, reducing the interfacial tension between water phase and oil phase by approximately 60%, and the water is coupled in beaded fashion, reducing water activity.
