Margen
If fresh pineapple leaves your tongue rough or a little stinging, it's not your imagination. It contains bromelain, an enzyme that breaks down proteins. While you eat it, it's busy dismantling a tiny bit of the protein in your mouth. It's not dangerous; your saliva and cells renew quickly, but the sensation is real.
That same enzyme explains a kitchen quirk: jelly won't set if you add fresh pineapple. Jelly is collagen, a protein, and bromelain cuts it up before it can solidify. The dessert stays liquid and nobody understands why.
The cure is heat. Cook the pineapple, or use the tinned kind (which is pasteurised), and the enzyme is deactivated and no longer bites. That's why pineapple in syrup does work in baking. Fresh, though, it has attitude: it eats you while you eat it.