Assessment of Heating Rate and Non-uniform Heating in Domestic Microwave Ovens

Abstract

Due to the inherent nature of standing wave patterns of microwaves inside a domestic microwave oven cavity and varying dielectric properties of different food components, microwave heating produces non-uniform distribution of energy inside the food. Non-uniform heating is a major food safety concern in not-ready-to-eat (NRTE) microwaveable foods. In this study, we present a method for assessing heating rate and non-uniform heating in domestic microwave ovens. In this study a custom designed container was used to assess heating rate and non-uniform heating of a range of microwave ovens using a hedgehog of 30 T-type thermocouples. The mean and standard deviation of heating rate along the radial distance and sector of the container were measured and analyzed. The effect of the location of rings and sectors was analyzed using ANOVA to identify the best location for placing food on the turntable. The study suggested that the best location to place food in a microwave oven is not at the center but near the edge of the turntable assuming uniform heating is desired. The effect of rated power and cavity size on heating rate and non-uniform heating was also studied for a range of microwave ovens. As the rated power and cavity size increases, heating rate increases while non-uniform heating decreases. Sectors in the container also influenced heating rate (p < 0.0001), even though it did not have clear trend on heating rate. In general, sectors close to the magnetron tend to heat slightly faster than sectors away from the magnetron. However, the variation in heating rate among sectors was only 2 °C/min and considered not practically important. Overall heating performance such as mean heating rate and non-uniform heating did not significantly vary between the two replications that were performed 4 h apart. However, microwave ovens were inconsistent in producing the same heating patterns between the two replications that were performed 4 h apart.