Grapes on Fire

Working at a boarding school, the most common reason the fire alarm goes off is a microwave incident (usually burnt popcorn). We all know that there are some things you shouldn’t put in the microwave – any kind of metal, most plastic containers, and Styrofoam.

But did you know that you shouldn’t microwave grapes?

In an experiment done in the video here. A grape is cut almost in half, covered with glass, and microwaved. After just a second you can start to see huge sparks coming from the grape in the microwave. What’s happening is that the two sides of the grape are acting as a focal point for the microwaves. As the microwaves move across the grape through the piece of skin left uncut, this tiny part of the grape skin quickly dies out and burns up, causing a spark. Image Credit

The spark ionizes the air around the grape, creating an ion-rich gas known as plasma. Plasma is one of the four fundamental states of matter which can be created by heating a gas or subjecting it to a strong electromagnetic field. This decreases the number of electrons, creating positive or negative charged particles called ions.

The sparks are big because the plasma conducts the electricity and can absorb the microwaves. The more it absorbs, the bigger it gets. The glass contains the air around the grape even more for a better light show.

A warning – this experiment can cause burn marks in your microwave.

While I don’t recommend experimenting with things in your microwave – if you have a microwave story, please share with us below! Have you ever microwaved a grape? What about ivory soap?