Grape in microwave

Image by Fernando Gutierrez-Juarez/picture alliance via Getty Images

People are obsessed with putting weird things in the microwave. From Peeps to iPhones, curiosity has led people to put all sorts of things into their microwaves, even if they don’t belong there. While loading your appliance up with metal will certainly create a spectacular light show, it’s also likely to turn your entire kitchen into an inferno. Thanks to science and a little curiosity, the people of the internet have found a much safer way to put on a show when the WiFi is out. Take a trip to the produce aisle, because you’re going to need some grapes.

Exciting times

Microwaves work by using—you guessed it—microwave radiation to alter the chemical state of objects placed inside. In the case of food, the radiation excites the water molecules, making them move around more. The molecules’ motion generates heat, which is how frozen food thaws and cold food warms up to an edible temperature. Due to the nature of waveforms, microwaves also have dead zones where the radiation cancels itself out. Those dead zones are what leave cold spots in your food. The longer food is left in the microwave, the more those water molecules wiggle and the hotter it gets. If left in there long enough, the heat produced by the dancing molecules excited by the radiation will eventually cook raw food.

In the case of metal in the microwave, the reaction between the molecules in the metal and the radiation is much more explosive. The excitement of the molecules in the metal, whether it’s aluminum foil, steel wool, or a silver fork, causes the buildup of an electric charge. With enough exposure, the charge stored in the metal often exceeds the dampening effect of the air that keeps the charge contained and the electricity arcs from one part of the metal object to another park, causing a spark. These sparks can get out of hand pretty quickly, leading to a fire or even an explosion. If your inner pyromaniac insists on creating an indoor light show, there’s a much safer option out there, and it uses grapes.

Grape balls of fire

Chances are pretty good that, if you’re reading this, you’ve microwaved stuff before. In your microwaving endeavors, you’ve likely never seen your food go up in flames, so why would a grape be any different? The answer all comes down to waves again. You should never run a microwave on empty unless you want to break it. Typically, the food you’re trying to heat up absorbs the radiation and keeps the latent levels relatively low. When the microwave is empty, there’s nothing there to absorb the radiation, and it builds up. When the electric fields inside the appliance get to high, you risk frying the whole thing. Adding something small to concentrate that field, like a grape, can lead to a fascinating (though still potentially destructive) light show.

When you microwave a grape, that high-intensity electric field suddenly has a very small place to gather. Under normal circumstances and wattage, your microwave should just make the grape really hot. If you turn up the power on your microwave and then nuke the near-nothingness that is a single grape, you’ll produce a bizarre reaction. A single grape, cut in half and placed so that the two halves are nearly touching, has a chance to generate plasma. The reaction isn’t a guarantee, but sometimes, the electric field inside the grape halves gets high enough that energy arcs from one half to the other. The energy discharge superheats the molecules between the two pieces, creating plasma. As cool as that sounds, you might not want to try this experiment at home. The chances of you frying your microwave while trying to generate plasma are pretty high.