Why sparks fly when you microwave grapes

[muriel_volestrangler]

YouTubers have gone grape crazy. In a plethora of internet videos, kitchen scientists have cut a grape almost in half—leaving just a strip of skin connecting the two sides—and stuck it in the microwave. In seconds, sparks erupt. Now, physicists think they know why this happens.
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To test this hypothesis, the researchers put grapes into microwaves and watched what unfolded with thermal cameras. Early on, the scientists found that a pair of grapes could also produce plasma, as long as they were kept within 3 millimeters of each other. If grapes can produce plasma without the skin strip, the researchers say, then the energy that produces the plasma must build up another way.

The thermal cameras revealed a hot spot between the grapes from a buildup of electromagnetic energy—not inside the grapes where the internet’s explanation would predict. This led the physicists to a new explanation: When two grapes are close to each other in a microwave, the waves they absorb bounce back and forth in the tiny space between them, creating an increasingly powerful electromagnetic field. This continues until the electromagnetic field becomes so powerful that it supercharges nearby electrolytes that then shoot out in a brief explosion of fiery plasma, the researchers report today in the Proceedings of the National Academy of Sciences.

https://www.sciencemag.org/news/2019/02/why-sparks-fly-when-you-microwave-grapes