Microwaving a grape can create a plasma, which is a gas charged with ions that produces tiny fountains of brilliant plasma that crackle from the spot where the grape halves connect. This phenomenon occurs because the grape can "trap" microwaves, meaning that when two connected halves of a grape are bombarded with radiation, microwaves that become trapped in the tissues of each half can use the connecting skin as a bridge, "hopping" from one grape hemisphere to the other. This results in a "hotspot" with a much stronger electromagnetic field in between the grapes, which generates the plasma.

It is not recommended to microwave grapes because they can trap so much energy in the microwave that they actually produce the same effect as lightning or the sun, which can damage the device. Additionally, microwaving one or two grapes will have the same effect as running the microwave empty, which can also damage the device. Therefore, it is not safe to microwave grapes, and it is not recommended to try this at home.