Physicists Explain Fireballs Leaving Grapes in the Microwave

In 2011, impressive videos of microwave-inflamed grapes became viral on YouTube. All one person had to do was cut a grape in half by leaving the two halves connected by a piece of skin to the bottom and heat them in the microwave. In a few seconds, a small ball of fire would appear between them. Making things even more exciting was that no one could explain it. Since then, many armchair scientists have presented possible explanations – one of the most popular being the suggestion that grapes are a sort of microwave antenna on the bridge of the skin. In this new effort, Canadian physicists have conducted numerous tests on grapes and other similar objects to find out the real reason for the formation of the fireball.

The tests consisted mainly of using thermal cameras to capture the action of heated grapes and to perform simulations. They also tested other similar fruits and plastic balls filled with water.

The researchers discovered that the formation of the fireball resulted from a simple process. When microwaves enter the grapes, hot spots form in the two rooms at the points where they are closest to each other, because of the connection that unites them. As the hot spots get hotter, the surrounding electrolytes become overfed, resulting in the formation of a plasma explosion in the form of a small fireball.

The researchers noted that the same effect could be achieved with similar sized fruits or balls filled with water. They also found that it was not necessary to maintain any physical connection between the two rooms. All that was needed was that they were not separated by more than three millimeters.

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More information:
Linking plasma formation in grapes to microwave resonances of aqueous dimers, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073 / pnas.1818350116