The computerized simulation of the electromagnetism and thermal defrosting were developed and validated to compare and understand the behavior of two heating processes (inverter and cyclic). Food exposure was simulated in a microwave oven cavity (2.45 GHz) using a computational model. The simulated rotational model of mashed potatoes was developed using a coding in COMSOL-MATLAB. The hot and cold spot patterns of the simulated temperature profile matched with the real ones. The heating of the mashed potatoes was not uniform in the product and the highest temperatures were observed at the edges (~ 90-95 °C). The center of the product reached temperatures of 20 °C. To compare traditional heating process, the cycling and the newest inverter, considered the shape and size of containers with mashed potatoes. The initial product temperature was -10 °C and thawed by microwave exposure for 6 minutes. The heating of the inverter did not produce differences in the absorption temperature of the mashed potatoes. The shapes and size of food are factors that affect the uniformity of heating. The small trays allowed the mash to reach an average temperature of 32 °C at 6 minutes of exposure. The round (small) and rectangular (large) vessel, allowed to reach an average temperature of 20 and 16 °C, respectively. Both types of heating presented a similar thermal non-uniformity, for the heating of mashed potatoes.