Assumptions:
- For American readers – I'm talking about Jello not Jam.
- in Australia Paw Paw refers to Papaya
I've got a box of Aeroplane Jelly that states:
DO NO ADD FRESH PINEAPPLE, KIWI FRUIT OR PAW PAW AS JELLY WILL NOT SET
My question is: Why does my jelly crystal box single out pineapple, kiwi fruit and paw paw as preventing setting? Why not orange or watermelon or plum?
Best Answer
Certain enzymes (proteases) cut the protein bonds that create the mesh that causes the jelly (or Jello, or gelatin) to, well, gel.
Orange, watermelon and plum do not contain enough of those enzymes to interfere with gelling. In addition to paw paw (more commonly known as papaya in the US), pineapple and kiwi; mango, ginger, figs and guava also contain enough of those enzymes to interfere with gelling.
The application of high heat will inactivate those enzymes to the point that they will no longer interfere with gelling. That's why you can use canned pineapple, but not fresh, in gelatin desserts.