Hard-boiled eggs are a dish best served cold.
When quickly reheated in a microwave and then pierced, the picnic staple can explode with a loud bang in a shower of hot, rubbery shrapnel. But this blast is far more likely to make a hot mess than hurt your hearing, according to research presented December 6 at the Acoustical Society of America meeting in New Orleans.
That distinction isn’t as odd as it might sound. In a lawsuit, a man claimed to have suffered burns and hearing damage after a microwaved, hard-boiled egg exploded in his mouth at a restaurant. Researchers from Charles M. Salter Associates, Inc. in San Francisco called as expert witnesses couldn’t find scientific papers backing up the claim that an egg could burst with enough vigor to cause hearing loss — just a lot of YouTube videos documenting eggsplosions.
So the researchers microwaved peeled hard-boiled eggs in water on high power for three minutes.
The eggs were “uncooperative,” study coauthor Anthony Nash said in a news conference. Some exploded in the microwave, while others wouldn’t explode at all. But of nearly 100 eggs tested, 28 exploded outside of the microwave after being poked with a meat thermometer. From 30 centimeters away, the sound pressure from those explosions ranged from 86 to 133 decibels.
The median sound pressure level recorded, 108 decibels, is about the same as that at an average rock concert. Continuous exposure to that noise level could damage hair cells inside ears that respond to sound. The National Institute for Occupational Safety and Health sets recommended exposure limits for sound pressures above 85 decibels, says William Murphy, a researcher at NIOSH who wasn’t part of the study. But those limits are based on daily exposure over years, he says.
A burst egg’s boom, on the other hand, lasts just milliseconds — not long enough to do much harm. “The likelihood for hearing damage from a single exploding egg was very low,” Nash said.
The lawsuit was settled out of court before Nash and his colleagues conducted the second phase of the study – considering how sound hits your ears when it’s coming from inside your mouth. An in-mouth explosion might send slightly more sound pressure to the ears, Nash says, but still probably not enough to cause lasting damage as a one-time accident.
A peeled egg probably explodes when pockets of water trapped in the yolk become superheated — hotter than the boiling temperature of water without actually bubbling, Nash suggested. When disrupted, say by a fork or a tooth, the water pockets spontaneously boil, bursting through the squishy egg white and sending bits flying. (It’s the same phenomenon that can occasionally make microwaved coffee spurt out of the mug onto your clean work clothes.)
A bigger risk than the noise might be the heat. Nash and his colleagues measured the temperature of yolks in eggs that didn’t burst. Those temperatures were, on average, 12 degrees Celsius above the surrounding water bath, which was often close to boiling.