18

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?

  • 3
    By paw paw do you mean papaya, a fruit sometimes called pawpaw: en.wikipedia.org/wiki/Papaya ? Common paw paw is a very different, custardy tasting, fruit: en.wikipedia.org/wiki/Asimina_triloba I'd be surprised if it contained large amounts of papain or any other protease. – Wayfaring Stranger Sep 26 '14 at 12:58
  • Sorry yes - Paw Paw is the Australian term for Papaya – hawkeye Sep 26 '14 at 13:14
  • 1
    Related – Peter Taylor Sep 26 '14 at 13:17
  • 4
    FWIW, my party trick is to bring crystal jelly with pineapples to potluck. And when my friends try it at home the jelly doesn't set. The secret is that chili peppers (especially red chilli) contains enzymes that counter the enzymes in pineapples and allow the jelly to set. Just cut be sure to remove all the seed before adding the chili to the jelly and remove the chili before it sets (unless you want people to know your secret) – slebetman Sep 27 '14 at 9:59
  • @slebetman Very interesting. I'm going to have to try that! Are red jalapenos OK to use? How much per 6oz box (170 grams, 8 servings)? – Jolenealaska Oct 3 '14 at 14:30
27

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.

  • 1
    Really appreciated the range of fruits you found here. – hawkeye Sep 26 '14 at 13:16
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    It might be more accurate to say "within the USA" rather than "outside of Australia". I knew it as pawpaw growing up in the UK, and according to Collins American Dictionary the use of pawpaw to describe Asimina triloba is specific to the US. – Peter Taylor Sep 26 '14 at 13:39
  • @PeterTaylor I'll buy that. Edited. – Jolenealaska Sep 26 '14 at 13:41
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    +1 for the very helpful information about heat deactivating the enzymes. – heathenJesus Sep 26 '14 at 17:31
8

From The naked scientist

Why does it happen? Jelly is made up of long thin protein molecules. The reason that jelly sets is that as the gelatin molecules tangle up as they cool creating a huge intertwined tangle which traps the water and makes a flexible solid.

The pineapple contains an enzyme called bromelain and kiwi fruit another enzyme called actinidin - both of these enzymes are proteases, which means that they will chop up protein molecules. In the same way that the digestive enzymes in your intestines break up proteins to allow you to digest them. This means that when they are mixed with gelatin, the proteases chop the gelatin protein up into pieces which are far too short to tangle, so the jelly doesn't set.

No mention on that website about Paw Paw but I would assume it is for the same reason.

6

Pineapple, kiwi and paw paw all contain enzymes that break down proteins (bromelain, actinidin and papain respectively). Since the setting agent in jelly is gelatin, which is mostly protein, using any of these fruits will interfere with the jelly setting.

  • Really nice simple answer - thanks! – hawkeye Sep 26 '14 at 13:15

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