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Why does pineapple stop jelly setting?

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When making some jelly last week, I noticed the packet said it wouldn’t set if pineapple, kiwi or papaya were added to it. We decided to find out why pineapple stops jelly setting.

Jelly with pineapple in it

What you need

  • Jelly cubes
  • Fresh pineapple
  • Tinned pineapple
  • Any other fruits you wish to test
  • Small bowls

Instructions

  • Make the jelly up as per the instructions.
  • Divide into several small bowls.
  • Add a different fruit to each bowl.
  • Leave one just as jelly – this is our control

Results

We found only the jelly containing the fresh pineapple did not set. In one bowl I had just two small pieces of pineapple, this was enough to stop it setting.

results of an investigation into why jelly doesn't set with pineapple

Why does pineapple stop jelly setting?

Jelly contains gelatine which partially consists of protein molecules. It sets because the protein molecules tangle up as they cool down trapping the water to make a solid. Fresh fruits such a pineapple, kiwi and papaya contain enzymes which break down these protein molecules, making them smaller, so they can’t tangle up, which stops the jelly setting. This is similar to how the enzymes in your stomach break down food.

The tinned pineapple jelly set because as part of the tinning process the pineapple has been heated  to destroy  bacteria. This process has also  destroyed the enzymes ( they are denatured ).

The enzyme in pineapple is called bromelain and the one in kiwi actinidin.

Jelly in a child's hands

Why does jelly set?

Jelly contains gelatin, which is a processed form of collagen. Collagen is the most common protein found in humans and other mammals. When the gelatin is dissolved in hot water the bonds holding the collagen protein together are broken.

As the gelatin cools new bonds form trapping the water between them.

Why does jelly wobble?

The liquid in the jelly is trapped between gelatin bonds which is why it wobbles!!

What is bromelain?

Bromelain is a protein-digesting enzyme mixture found in the stem, fruit, and juice of the pineapple plant.

Bromelain has also been used to medicinally for centuries as it has anti inflammatory properties.

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Reader Interactions

Comments

  1. What another fab experiment – I knew about Kiwi but didn’t know others not setting jelly – I really like with the tinned pineapple and the denatured enzymes – wouldn’t this be great to do with GCSE Science students in the enzyme work

    Reply

  8. So I’m a grown up! But this is is v useful info that I didn’t know. I found it through my need to make pineapple flummery mousse and checking if ok to use tinned pineapple. It is! Thanks Science Sparks!

    Reply

Trackbacks

  2. […] Some fresh fruits do better than others in homemade gelatin. Pineapples, kiwi fruit, papaya, figs, and prickly pears all contain an enzyme called protease. This enzyme helps digest proteins, and since gelatin’s structure holds up due to its protein content, these fruits will prevent it from setting properly. If you’re dead set on using these fruits in your homemade gelatin, all but kiwi can be peeled, cubed, and boiled for at least five minutes to neutralize these enzymes. You can also use pasteurized juices from these fruits, which have gone through a heating process as well (1). […]

    Reply

  3. […] Some fresh fruits do better than others in homemade gelatin. Pineapples, kiwi fruit, papaya, figs, and prickly pears all contain an enzyme called protease. This enzyme helps digest proteins, and since gelatin’s structure holds up due to its protein content, these fruits will prevent it from setting properly. If you’re dead set on using these fruits in your homemade gelatin, all but kiwi can be peeled, cubed, and boiled for at least five minutes to neutralize these enzymes. You can also use pasteurized juices from these fruits, which have gone through a heating process as well (1). […]

    Reply

  4. […] Some fresh fruits do better than others in homemade gelatin. Pineapples, kiwi fruit, papaya, figs, and prickly pears all contain an enzyme called protease. This enzyme helps digest proteins, and since gelatin’s structure holds up due to its protein content, these fruits will prevent it from setting properly. If you’re dead set on using these fruits in your homemade gelatin, all but kiwi can be peeled, cubed, and boiled for at least five minutes to neutralize these enzymes. You can also use pasteurized juices from these fruits, which have gone through a heating process as well (1). […]

    Reply

  5. […] Some fresh fruits do better than others in homemade gelatin. Pineapples, kiwi fruit, papaya, figs, and prickly pears all contain an enzyme called protease. This enzyme helps digest proteins, and since gelatin’s structure holds up due to its protein content, these fruits will prevent it from setting properly. If you’re dead set on using these fruits in your homemade gelatin, all but kiwi can be peeled, cubed, and boiled for at least five minutes to neutralize these enzymes. You can also use pasteurized juices from these fruits, which have gone through a heating process as well (1). […]

    Reply

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