Why You Should Not Heat a Cup of Water in the Microwave

Have you ever heated a cup of water in the microwave? Chances are you’ll never do it again after reading this.

Before I explain why you shouldn’t heat up a cup of water in the microwave, let’s first discuss how a microwave works. The microwave has a part that produces electromagnetic waves, more specifically microwaves. These microwaves, with a wavelength of 1 mm to 1 m, are send through your food to heat it up. Your food exist of molecules, like everything essentially does. The microwaves cause vibration of those molecules and therefore heat is produced. Nevertheless, not every molecule produces heat at the same rate. Molecules like fats or carbohydrates produce heat faster. The molecules that don’t heat that easily are then heated because of the heat transfer through the produced steam. This process is the reason why you’re food often isn’t heated evenly.

Now let’s see what happens if you warm a cup of water. The microwaves have so much energy that they’ll easily warm your cup of water to a temperature higher than 100 °C. Essentially, if it starts boiling, there’s no problem. The problem only arises when the water does not boil at 100 °C, but gets superheated. Superheated water is a stable form, so if not interrupted, nothing will happen. The danger is that only one small heterogenic element is necessary for the boiling process to start. The cup exists of millions of water particles, so if the boiling process starts, every particle immediately transfers from the liquid phase to the gas phase. This phase transition releases an enormous amount of energy, hence the  stability is increased by transferring to the gas phase, resulting in an explosion. Normally, the worst that can happen is that you have to buy a new microwave, but caution is necessary: you’ll never know when the boiling process will start.

Despite what you might think, heating up a cup of soup or any other beverage will not cause any harm. In these beverages, there are heterogenic particles and the water will not get superheated. So next time you’d like a cup of tea, think twice before heating it up in the microwave!

Sources:
http://sieplex.com/article/oververhit-water
https://en.wikipedia.org/wiki/Superheated_water