Can Water Explode in a Microwave?
Microwaves heat food by exciting water molecules. Since water molecules are asymmetrical, they rub together when excited, and the resulting friction produces the heat that cooks the food. Symmetrical molecules generate significantly less friction when excited by microwave radiation, which is why microwaved food can be hot while the outer edge of the plate remains relatively cool. As water reaches the boiling point (212º F, 100º C at sea level), bubbles form as the liquid converts to steam. When water is heated in a smooth vessel in a microwave, there is no place for bubbles to form. The water continues to heat beyond the boiling point without actually boiling, in a phenomenon known as superheating. If the water is then agitated (as by putting a spoon into the cup, for instance) bubbles will immediately form and the water will boil instantaneously. Since liquids expand as they convert to gases, this means that the water will "erupt," possibly causing severe burns. To more safely boil water in a microwave, place a wooden skewer or bamboo chopstick in the water before microwaving. This will give bubbles a place to form so that the water can boil without superheating.