Kathleen Purvis Q&A

Is superheating really a microwave danger?

February 19, 2013 

Q. A friend forwarded an email warning about putting the handle of a wooden spoon in the cup before you heat water in the microwave. It’s supposed to keep the water from getting so hot it explodes. Is that true?

Like many things on the Internet, it’s sort of true and much more not true. If the email has a long tale of a 26-year-old man who was burned, well, that’s a classic sign of an urban legend that gets clicked and forwarded without end.

Superheating, the phenomenon described, can happen if you microwave water for a long time in a cup that is very clean or has no imperfections in the glass. Anything on the surface of the glass would create disruptions in the water that would form bubbles, helping heat to dissipate. Without that, heat can build up, causing the hot water to bubble up or splash when the surface is disturbed.

If you’ve ever microwaved water and seen it bubble up when you add sugar, that’s a small example of superheating.

However, superheating enough to cause a hazard is rare and only happens under just the right conditions. Most of us don’t microwave water for more than a couple of minutes. If you are really worried, adding something nonmetallic – from a chopstick to a wooden spoon – can disrupt the surface of the water, helping to release some heat. But the chance of a truly dangerous case of superheating is as unlikely as finding the identity of that 26-year-old man.

Email questions about cooking and food to Kathleen Purvis at kpurvis@charlotteobserver.com.

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