An electromagnetic cooking device comprising: an enclosed cavity (20, 222) in which a food load is placed; a plurality of RF feeds (26A-26D, 226A-226B) configured to introduce electromagnetic radiation into the enclosed cavity (20, 222) to heat up and prepare the food load, the plurality of RF feeds (26A-26D, 226A-226B) configured to allow measurement of forward and backward power at the plurality of RF feeds (26A-26D, 226A-226B); and a controller configured to perform the following steps: a) cause the generation of RF excitations at a specified frequency and phase shifts from each of the plurality of RF feeds (26A-26D, 226A-226B) for a predetermined time period; b) during the predetermined time period: measure and analyze the backward power at the plurality of RF feeds (26A-26D, 226A-226B) to calculate efficiency, determine a coefficient of variation in the efficiency, and monitor the coefficient of variation to identify possible changes in a characteristic of the food load; and c) repeatedly perform steps a) and b) until such time that a possible change is identified in a characteristic of the food load based on changes in the coefficient of variation over a cooking cycle, wherein the RF excitations are at different frequencies and/or phase shifts in accordance with a heating strategy for other predetermined time periods. an enclosed cavity (20, 222) in which a food load is placed; a plurality of RF feeds (26A-26D, 226A-226B) configured to introduce electromagnetic radiation into the enclosed cavity (20, 222) to heat up and prepare the food load, the plurality of RF feeds (26A-26D, 226A-226B) configured to allow measurement of forward and backward power at the plurality of RF feeds (26A-26D, 226A-226B); and a controller configured to perform the following steps: a) cause the generation of RF excitations at a specified frequency and phase shifts from each of the plurality of RF feeds (26A-26D, 226A-226B) for a predetermined time period; b) during the predetermined time period: measure and analyze the backward power at the plurality of RF feeds (26A-26D, 226A-226B) to calculate efficiency, determine a coefficient of variation in the efficiency, and monitor the coefficient of variation to identify possible changes in a characteristic of the food load; and c) repeatedly perform steps a) and b) until such time that a possible change is identified in a characteristic of the food load based on changes in the coefficient of variation over a cooking cycle, wherein the RF excitations are at different frequencies and/or phase shifts in accordance with a heating strategy for other predetermined time periods. a) cause the generation of RF excitations at a specified frequency and phase shifts from each of the plurality of RF feeds (26A-26D, 226A-226B) for a predetermined time period; b) during the predetermined time period: measure and analyze the backward power at the plurality of RF feeds (26A-26D, 226A-226B) to calculate efficiency, determine a coefficient of variation in the efficiency, and monitor the coefficient of variation to identify possible changes in a characteristic of the food load; and c) repeatedly perform steps a) and b) until such time that a possible change is identified in a characteristic of the food load based on changes in the coefficient of variation over a cooking cycle, wherein the RF excitations are at different frequencies and/or phase shifts in accordance with a heating strategy for other predetermined time periods.