When Nutella is heated in a microwave, the outside can become very hot while the inside remains relatively cool due to differences in the way heat is transferred through the substance.
Microwaves work by generating electromagnetic waves that excite water molecules, which causes them to vibrate and generate heat. Nutella, like many other food items, contains both water and fat. Water molecules tend to absorb microwave energy more readily, while fats do not absorb microwaves as effectively.
During the microwave heating process, the water molecules in Nutella absorb the microwave energy and rapidly heat up, which contributes to the hot outer layer. However, the fat content in Nutella does not absorb microwaves as efficiently. As a result, while the outer layer of Nutella becomes hot, the heat transfer to the inner portions, where the fat is more dominant, is slower.
Additionally, Nutella has a thick and viscous consistency, which can impede the distribution of heat throughout the product. The heat generated by the microwave may take time to penetrate the thicker portions of Nutella, leading to a temperature difference between the outer layer and the inside.
It is important to be cautious when heating Nutella or any other food in the microwave to avoid uneven heating. Stirring or rotating the Nutella during the heating process can help distribute the heat more evenly and minimize the temperature discrepancy between the outer and inner portions.