system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why won’t jello set if you add pineapple or kiwi?
gpt
Pineapple contains an enzyme called bromelain which breaks down proteins, which coincidentally is the stuff that makes jello "jello".

If you *cook* the fruit and break down the enzymes via heating then you remove this ability. That's why any jello that contains kiwi or pineapple will always use the canned versions, because they have been heated during the pasteurization process and the enzymes have been neutralized.