What Happens When You Microwave a Boiled Egg

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If you’ve ever used a microwave oven in your life, you probably know this already: Do not microwave an egg.

Of course, a quick search on YouTube will show that numerous individuals, perhaps with more curiosity than good sense, have gone ahead and done it anyway.

In one video, a man heats a peeled hard-boiled egg in the microwave. Removing it gingerly, he stations himself several feet away and reaches out with a fork. As the tines pierce it, the egg explodes like a tiny, protein-rich grenade. His friends shake with silent laughter as a dog moves in to lap up the quivering fragments.

Exploding eggs aren’t all fun and games, however — if one detonated in your mouth, you might not be laughing. In fact, a recent investigation into exactly how microwaved eggs go off, and the volume of the resulting boom, was set off by a lawsuit. A report on the research was presented at the Acoustical Society of America meeting in New Orleans on Wednesday.

A diner at a restaurant claimed that in addition to burns, his hearing had been damaged when he bit into a reheated, hard-boiled egg. Anthony Nash and Lauren von Blohn, acoustics experts at Charles M. Salter Associates, were engaged to look into whether the sound could be damaging.

And so began a long campaign of microwaving eggs, setting them under a microphone and giving them a prod. Nearly 100 eggs were sacrificed for the cause, and while most did nothing but lie there, about a third exploded gratifyingly (some also burst inside the microwave before getting to the microphone). Mr. Nash, who presented the research, said that at first they microwaved the eggs in a water bath, as the restaurant did, but very quickly realized they needed to change their method.

“After cleaning the microwave twice,” he said, “we decided to use an acoustically transparent container for the egg,” a nylon stocking that kept the egg from covering the microwave — or the carpet — with yolky shrapnel.

It soon became clear that the sound of the eggs going off, while loud, wasn’t particularly dangerous at a distance of one foot, ranging from 86 to 133 decibels. The exploding eggs were quieter, for instance, than a shotgun blast of 160 decibels, which is not considered harmful.

But the pair found something else. When they took the temperatures of the water bath and the egg yolk just after it exploded, there was a very large difference, averaging 22 degrees Fahrenheit. The yolk was hotter than 212 degrees Fahrenheit — in other words, hot enough to boil water. This suggested a potential explanation for this tendency to explode.

As an egg is cooked, the proteins inside the yolk clump together. Tiny pockets of water form as well, scattered throughout the matrix. These are harmless if you eat the egg after it cools. But if the egg is reheated and the yolk proteins rise above 212 degrees Fahrenheit, they could heat the water up to that temperature as well. Still under pressure within the egg, the water might not boil. But if the egg was penetrated or otherwise disturbed, that could all change swiftly, with the water instantly erupting into steam and provoking an explosion.

The lawsuit has since been completed, and thus the research into what is happening within the yolk of an exploding egg is unlikely to progress further in his hands, Mr. Nash said. But if the past is anything to go by, the empirical work by scores of amateurs with a smartphone, a microwave and a desire for excitement will probably continue — regardless of safety warnings.