Microwaves, for all the convenience they offer with frozen dinners and day-old leftovers, can make sparks fly in all the worsts ways if you try to reheat something which doesn’t belong. You’re hopefully aware that microwaving metal can create damaging sparks, but perhaps you’ve heard the slightly odder advice that grapes will explode inside of a microwave. That sounds like it’s a silly, untrue statement designed to test a friend’s gullibility — how can a grape be a fire hazard? However, it’s true that you should think twice before putting grapes into a microwave, because strange and seemingly fiery things can happen while it’s spinning around in there.
The grape doesn’t exactly explode, but it will appear to briefly catch fire, which can be a safety risk. More specifically, a bright jet of plasma can erupt from the tiny grape before sputtering out. To get the biggest jet possible — which again, you should not do — requires nearly cutting the grape into halves with a tiny bit of the grape skin connected to both. It’s an unusual bit of food science, and scientists only recently performed an in-depth examination into what makes a grape “explode.” There’s no fire inside your grape; the answer involves how microwaves uniquely mess with the water inside the little fruit.
Microwaved grapes create plasma jets
You’re likely familiar enough with how to spark a flame using a match or a lighter. In a scientific sense, plasmas like fire are created when a gas is heated in a way which ionizes it (or causes it to lose electrons). On another note, microwaves work by bouncing microwave radiation around and causing water molecules inside the food to vibrate, and this can unevenly heat up food. What happens when these two things mix together? According to a study published in 2019 in Applied Physical Sciences, when a grape (which is 82%water) is placed into a microwave, those molecule-vibrating microwaves get trapped inside of cavities in the grape. With nowhere to go, the trapped electromagnetic waves heat up the water so much until they ionize and ignite into plasma. Then, voilà: the grape appears to burst into flames when you set the microwave’s power too high.
Is a flaming grape dangerous enough to do serious damage to your home? Perhaps not, but it’s a big enough spark that it can damage your microwave. Plus, once it’s all said and done, the grape will look mushy and smell burnt, and there’s nothing much to do with it besides toss it. It’s a slightly worse scenario than a microwave ruining your coffee’s flavor, and it’s all the more reason to not try this at home. Now that you know to keep grapes out of the microwave, check out other common things you should think twice about before microwaving.
