If you mount a pickle on two metal forks and plug it into a socket, one end will light up in a brilliant orange glow. It’s a classic K-12 science demonstration, but the exact physics behind the illumination has long remained a mystery.
Josh Méndez, an assistant professor of electrical engineering at Portland State University, was surprised to learn that the glowing pickle was still an unsolved electrostatics problem. As a scientist with an interest in obscure electrostatic problems, Mendez felt called to delve into the pickle jar. More than 100 burnt pickles later, he is finally approaching an answer.
Because pickles are soaked in salty brine, they readily conduct electricity. When a current passes through, two competing theories usually explain the resulting glow: a spark discharge or igniting hydrogen gas.
The first theory relies on vapor sparks. As current heats the pickle, it boils off liquid, leaving behind gas pockets and a pungent smell of burnt pickle mixed with hot metal. However, the gas pockets also stop the flow of electrical current causing the pickle to cool down. When this happens, the gas pockets shrink and the conductive brine comes back toward the electrode.
“As that water comes back in toward the electrode a little arc crosses between the liquid and the electrode, just as when you reach for a doorknob and you get a zap,” Méndez said. “That doesn’t explain everything that happens, though.”
For instance, it doesn't clarify why only one end glows.
The second theory points to chemical ignition via electrolysis, which splits the brine's water into oxygen and volatile hydrogen ions. Hydrogen is only produced at the negative electrode, which may explain why the pickle glows on only one side. In this scenario, the glow comes from tiny hydrogen explosions trapped inside the pickle caused by the intense heat from the electrodes.
Méndez’s research indicates the real cause is a hybrid of both theories: the electrical spark actively ignites the hydrogen gas.
“There is hydrogen involved, but it's actually not heat that's igniting it — it's the spark,” Méndez said. “It's just like why you don't light a cigarette at a gas station. You're producing a spark that ignites the gas.”
As for the color? That comes down to pure chemistry.
“You're exciting sodium ions, which produce that characteristic orange glow,” Méndez said. “If you were to pickle something in a different salt, you'd get a color unique to those elements.”
It turns out the secret behind this classroom experiment isn't a high-tech breakthrough — it's just a very excited, slightly explosive pickle.