A microwave appliance provides safe heating of packaged food products at an efficiency greater than 90%. A temperature sensor positioned about a product holder is configured to sense a temperature of the package. A product identification scanner identifies a type of food product, a type of packaging, and/or a size of packaging being inserted into the microwave appliance. The product identification may be used to obtain a dielectric constant and/or electrical conductivity of the product. An electric field detector verifies that a suitable product has been inserted into the microwave appliance and is used to estimate a volume of the packaged food product. Accordingly, even partially full packaged food products may be safely re-heated to a desired temperature. As opposed to a time-based operation with traditional microwave appliances, operation of the microwave appliance may be adjusted based on the product identification scanner, temperature sensor, and electric field detector.