What do you think of this fact?
You bite into fresh pineapple, and after a few pieces your tongue starts tingling. Sometimes your whole mouth feels raw. You’re not imagining it. While you’re eating the pineapple, it’s breaking down a tiny bit of you.
An enzyme that cuts up protein
The culprit is bromelain, a mix of enzymes found only in pineapple. Bromelain is a protease, an enzyme that chops proteins into smaller pieces. According to Live Science, it goes after mucins, the proteins that make up the protective mucus layer in your mouth. Once that layer gets nibbled away, the tissue underneath is more exposed.
Then there’s the acid. Pineapple has a pH of about 3 to 4, so it’s pretty sour. That acid hits the weakened lining, and that’s the tingling or burning you feel. According to Live Science, the amounts in the fruit aren’t dangerous, just uncomfortable.
The jelly test
You can see bromelain at work in the kitchen. Try making jelly or Jell-O with fresh pineapple: it won’t set. Gelatin is made of long protein chains that tangle up as they cool and form the gel. According to The Naked Scientists, bromelain chops these chains into pieces that are too short to tangle.
Canned pineapple works, though. During canning the fruit gets heated, and the heat destroys the enzyme. That’s also why grilled pineapple doesn’t make your tongue tingle anymore.
Fresh kiwi and papaya also contain protein-cutting enzymes and will ruin your jelly too.
A superpower for meat
What’s annoying in your mouth is handy in the kitchen. Because bromelain breaks down proteins, pineapple works as a meat tenderizer in marinades. The Naked Scientists suggest these enzymes may originally have helped the plant fend off pests, since animals and bacteria are largely made of protein.
Pineapple: the only fruit that politely nibbles back.