Microwaved food may appear to cool down quickly for a few reasons:
Surface-to-Volume Ratio: Microwaves heat food by producing electromagnetic waves that excite water molecules within the food, generating heat. However, this heating primarily occurs on the surface of the food. As a result, the outer layers of the food can become significantly hotter than the inner portions. When you remove the food from the microwave, the hot surface quickly loses heat to the surrounding cooler air, causing it to cool down rapidly.
Evaporation: Microwaving can heat liquids within the food, such as water or oil. When these liquids reach high temperatures, they can undergo rapid evaporation. Evaporation involves the transformation of liquid molecules into a gaseous state, and this process requires energy, which is drawn from the surrounding environment. As a result, evaporation cools down the food quickly.
Lack of Thermal Insulation: Most microwavable containers are not effective thermal insulators. When you place hot food in a container and remove it from the microwave, the heat can escape from the food into the container and then into the surrounding environment. If the container is made of a material with good thermal conductivity, such as ceramic or glass, the heat loss will be even more significant, causing the food to cool down rapidly.
It's worth noting that even though the surface of the food cools down quickly, the inner portions may still retain a significant amount of heat. Therefore, when reheating microwaved food, it's essential to ensure that it is heated evenly to reach a safe and enjoyable temperature throughout.