Crush a Wintergreen Mint in the Dark and It Sparks

Sugar is a crystal, and crystals do not enjoy being snapped in half. When a lump of hard sugar fractures, the two fresh surfaces are left holding opposite electrical charges for a fraction of a second, and the charge leaps the gap it has just made. That is a genuine, if very small, bolt of lightning going off inside your snack. The effect has a properly serious name: triboluminescence, from the Greek for rubbing.

Plain sugar does this on its own, but the flash is feeble and mostly ultraviolet, which your eyes politely ignore. Wintergreen flavouring is the accomplice. Methyl salicylate, the oil that gives wintergreen its cool medicinal snap, is fluorescent: it absorbs that invisible ultraviolet and hands it straight back as bright blue light you can actually see. A wintergreen mint therefore out-sparkles everything else in the sweet aisle.

To try it you need a properly dark room, about five minutes for your eyes to adjust, and either a mirror or a friend willing to stare into your open mouth. Then bite down hard. The blue flickers are quick and slightly startling, and the whole thing looks far more like a magic trick than the mechanical failure of a sugar crystal, which is exactly what it is.

None of this is new. A writer in the early 1600s described the sparks that fly when hard sugar is scraped with a knife, so sweets have been putting on this show for at least four centuries with almost nobody watching. Sugar is not even the strangest case: peel ordinary sticky tape in a vacuum and it emits X-rays, which is a fine reason to look at your desk drawer with mild suspicion.