Why do pickles glow? Researcher investigates explosive answer

When a pickle is plugged into a socket with two metal forks, one end glows orange. This phenomenon is a well-known K-12 science demonstration, but the exact scientific explanation has remained a mystery. Researchers from Portland State University, including assistant professor Josh Méndez, have been investigating this electrostatics problem.

Pickles are soaked in salty brine, which allows them to conduct electricity. When an electrical current passes through the pickle, two dominant theories attempt to explain the glow: a spark discharge or the ignition of hydrogen gas. The spark discharge theory suggests that vapor sparks form as the pickle heats up, causing gas pockets to develop and a pungent smell of burned pickle and hot metal.

However, these gas pockets also impede electrical current flow, causing the pickle to cool down and the brine to return to the electrodes. This then creates a small spark arc, similar to when you touch a doorknob and receive a shock. The electrolysis theory posits that chemical ignition occurs through the splitting of brine water into oxygen and volatile hydrogen ions.

Hydrogen is produced primarily at the negative electrode, which could explain why only one end of the pickle glows. In this case, the glow comes from tiny hydrogen explosions caused by the intense heat from the electrodes, trapped inside the pickle. Méndez's research indicates that the real cause is a combination of both theories: the electrical spark actively ignites the hydrogen gas.

The orange color of the glow is due to the excitation of sodium ions, which produces a unique glow depending on the type of salt used in pickling. Ultimately, the mystery behind the glowing pickle is not a high-tech breakthrough but rather a very excited, slightly explosive pickle.