Why does water boil with froth in a microwave?

Answer by  rightlight (1053)

Sometimes water can reach a super heated state while being boiled in a microwave. Water, with no foreign substance present, will sometimes not boil until it is removed from the microwave.

Answer by  Skullwing (746)

Microwave ovens work by vibrating the water molecules in the food so that they heat up and cook whatever is around them. Because of the way it effects water, it actually causes the water to super-heat as a liquid well above its natural boiling point. The froth is super-hot water touching dust particles or other contamination, which releases the steam.