Why does pineapple burn your tongue?
The Real Answer
Pineapple contains bromelain, an enzyme that breaks down proteins. Your tongue is made of protein, so bromelain literally digests the surface layer of your mouth, causing that raw, burning sensation. Cooking or canning pineapple destroys bromelain, which is why canned pineapple doesn't hurt. Fresh pineapple also contains citric acid, which adds to the burn.
You're eating the only fruit that eats you back. It's not sweet—it's a small protein-dissolving attack that tastes like Hawaii. Your mouth is being chemically dismantled while you're pretending it's refreshing.
Why People Ask This
Most people grow up eating pineapple and just accepting the burn as part of the deal, like it's a flavor. Then one day you learn it's actually an enzyme dissolving your mouth and suddenly you're suspicious of all tropical fruit. The fact that canned pineapple doesn't do it makes you realize you've been voluntarily letting fruit digest you this whole time.