If you have a grape, a knife, and a microwave you don't mind potentially ruining, you can make plasma at home. (Warning: this may ruin your microwave.)
The process is simple: you cut a single grape nearly in half, leaving a bit of skin connecting the two halves, then microwave it by itself. As Australian physicist Stephen Bosi shows in the video above, after a few seconds, you'll see sparking and a plume of plasma — a stream of charged particles called ions — leaping from one half to the other, then rising upward.
Here's how it works: microwaves normally cook food by sending microwave radiation through it, which agitates the water molecules, causing them to vibrate and generate heat.
But in this case, since there's not enough food in the oven to absorb these microwaves, they become so concentrated in the grape tissue that they rip some of the molecules apart, generating charged ions. There are also some ions already present in the grapes — electrolytes.
Due to the particular size of the grapes and the frequency of the concentrated microwaves, an electromagnetic field forms, causing these ions to flow from one grape half to the other. Initially, they pass through the flap of skin, but eventually, they leap through the air. This causes some of the surrounding air to ionize as well — producing the extremely hot, bright plumes of plasma that you see rising upward in the video.
However, there's a hitch: this plasma can damage the microwave, and running it empty (or in this case, nearly empty) isn't a good idea in general, as the unabsorbed radiation can damage it as well. So if you care about your microwave, you should only do this for a few seconds — or just watch the many videos of this phenomenon posted on YouTube.