Ever notice that some fatty foods reheated in the microwave seem to heat up much faster and hotter than other foods? What gives?
Water Should Heat Faster than Oil
Recall that microwaves act mainly on water in food, causing the water molecules to vibrate and rotate, which heats up your food. Microwaves also affect fats and sugars, but to a much lesser extent than water. So fats should actually take longer to heat up because they are less affected by microwave radiation. Practically speaking, this is not always what we observe when we heat fattier foods.
Consider the Heat Capacities
We need to look at the heat capacities of water and oil to better understand this situation. Oil has a lower heat capacity than water, which translates into oil requiring less energy to heat up than water does. In other words, it is actually "easier" to heat oil than water. So even though water absorbs more microwaves than oil (and fats in foods), oil will heat up faster in the microwave.
Consider the Boiling Points
Water has a boiling point of 100°C at sea level, while olive oil, for example, has a boiling point of 300°C. When you heat up something that is more fat than water, that food can actually reach a much higher temperature when heated in the microwave than a watery food.
Even though fats absorb less microwave radiation, since it is easier to heat fats than it is to heat water, fats actually heat up faster in the microwave. And since oil boils at a higher temperature than water, you can heat oil to a much higher temperature, which is why fatty foods seem to get much hotter than watery foods.
Of course, all this depends on the foods you are heating; the results can vary. Are there any foods that you find microwave hotter and faster than others?