Why Do Grapes Spark When Microwaved? A New Study Delves Into The Answer


When a scientific study opens with “It is a truth universally acknowledged that a pair of grape hemispheres exposed to intense microwave radiation will spark, igniting a plasma,” you know things are about to get interesting. And that’s just what happened when a group of researchers delved into exactly why grapes spark when placed in the microwave.

Many items, when placed in a microwave, can create strange or shocking results. Anyone who has ever heated an item containing metal in the microwave will attest to this. But have you ever wondered why your grapes spark when trying to heat them in the microwave? Assuming you’ve ever tried, that is. Because, let’s face it, there isn’t really such a need for heated grapes.

According to a new study released by Hamza K. Khattak, Pablo Bianucci, and Aaron D. Slepkov on PNAS, regardless of why you might want to heat your grapes, there is a reason why they act so strangely when placed in the microwave.

What is known about grapes sparking when placed in a microwave is that you need to cut a grape most of the way through so that it is still joined by a small amount of grape skin. Then you place it on a plate and cover it with a glass before microwaving it on high. After a few seconds, the grapes will begin to spark. For those of you who have never tried this nifty parlor trick, there is a YouTube video that explains exactly how to do it.

However, the science of why this happens has now been explored by a group of researchers.

“This is a regime that hasn’t been significantly studied before,” one of the paper’s authors, Pablo Bianucci, told Gizmodo.

The researchers used not only grapes in the experiment, but also hydrogel beads, due to their high water content. They then set about exploring the phenomena. They quickly discovered that the myth of keeping the grapes joined together by a thin piece of skin was not required to create the spark, as demonstrated by the hydrogel beads.

It was discovered that when two touching water-filled circular objects are placed in an electromagnetic field (the microwave), a hotspot is created where the items intersect. Thanks to this concentrated hotspot, the energy become so great that plasma is created by the ions in the touching area. Thus, a spark or flare of flame is seen in the microwave.

And all joking aside regarding why such detailed research was conducted on sparking grapes, the scientists involved in the study did offer some valid reasons why this research is important.

University of Illinois chemistry professor Catherine Murphy, who edited the paper, believes that this research can be used further in relation to “other directed-energy systems, such as explosives or high-intensity laser pulses,” according to Gizmodo. In fact, identifying how the high-water spheres can create such a hotspot will likely lead to advances in photonics further on down the track.

As for whether people at home should also be experimenting with grapes in their own microwaves? One needs to take heed because, according to Ars Technica, the researchers managed to destroy 12 microwaves in the process of their research.