Microwave Heating

Microwave heating takes place in nonconductive material due to the polarization effect of electromagnetic radiation at frequencies between 300 MHz and 300 GHz. Started as a by-product of the radar technology developed during World War II, the domestic microwave oven is now a common appliance in households. Microwave heating has found many applications in the food processing industry, including tempering of frozen foods for further processing, pre-cooking of bacon for institutional use, and finishing drying of pasta products. In those applications, microwave heating demonstrates significant advantages over conventional methods in reducing process time, improving food quality, and reducing environmental impacts. Plastic packaging materials are transparent to microwaves. Microwaves can, therefore, be used to process pre-packaged food products. Microwave sterilization can have a major advantage over conventional retorting because of the relatively short heating time and potential to produce high quality self-stable food products.

Two frequency bands are allocated in the USA by the Federal Communications Commissions (FCC) for industrial, scientific, and medical (so called ISM) applications. The 915 MHz band is used for industrial heating only, and the 2450 MHz band is used both in the industry and in domestic microwave oven. Dielectric properties of foods play a critical role in determining the interaction between the electric field and the foods, and they are dependent on composition, temperature and microwave frequency. Successful exploration of microwave heating applications relies on a thorough understanding of the interaction between microwave heating and foods, and on the ability to predict and provide a desired heating pattern in foods for specific applications. The microwave heating research team at Washington State University works closely with industrial and government partners and uses modern computation simulation and property measurement tools to develop microwave sterilization technology for commercial applications.