Abstract
This report describes the results of experiments to determine how the runaway and edge effects of microwaves on foods can be reduced. A technology using microwave is very useful for heating or sterilizing food, especially for high viscosity foods or those foods containing solid foodstuffs. However, this technique has some problems such as runaway and edge effects. The former results from the difference in dielectric constants of used foodstuffs and the latter from the concentration of energy at the corners of packages or at sharp edges. For the sake of resolving these problems, we examined whether the shapes of a package, the scattering of microwaves under stirring conditions and the use of microwaves under a steamed atmosphere would be beneficial. As experimental foods, Okara, chikuzenni and cream cheese were used. A round package was less scorched at edges than a square one. The circulation of warm air into the chamber did not reduce the edge effects. Irradiation with microwaves under a steamed atmosphere substantially reduced both the runaway and edge effects. The foods were heated uniformly and the uniform electric fields were observed at all places of package. We proposed that the cause of this phenomenon is the phase translation of steam. The results of this study indicate that irradiating foods under an atmosphere of steam with microwaves increase the uniformity of the heating process.
