Variable frequency microwave heating of food

Industrial microwave food processing is universally based on single frequency microwave sources. With the emergence of variable frequency microwave ovens, it is possible to exploit the frequency dependence of a food's permittivity and/or choice of heating frequency, for example as a new route to achieving targeted heating. Variable frequency heating procedures are developed to overcome the geometry of a roughly spherical foodstuff dominating the heating pattern when heated in fixed frequency applicators. Target mean temperatures of 55, 75 and 90 degrees C within 2 minutes and without physical damage were set; means of 54.5 +/- 4.1, 75.1 +/- 4.7 and 87.6 +/- 3.5 degrees C respectively were achieved within the time constraint and with no major physical damage, based on combining 8 discrete frequencies between 2.4 and 6.2 GHz.