Abstract: A microwave cooking appliance performs controlled beverage warming using a temperature sensor to capture a thermal image of a beverage in a cooking cavity. One or more sensing locations within the thermal image that are suitable for determining the temperature of the beverage are determined in part by ordering temperature readings from the thermal image by temperature to determine a temperature function and then determining locations in the thermal image that correspond to the beverage by calculating a derivative function over at least a portion of the temperature function.