The Science Behind Why Pineapple Ruins Gelatin

A knife stuck in yellow Jell-O
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You may have heard that adding pineapple to Jell-O or other gelatin will prevent it from gelling and it's true. The reason pineapple prevents Jell-O from setting is due to its chemistry.

Pineapple contains a chemical called bromelain, which contains two enzymes capable of digesting proteins, called proteases. Jell-O and other gelatins get their structure from links formed between chains of collagen, which is a protein. When you add pineapple to Jell-O, the enzymes links as fast as they form, so the gelatin never sets up.

Other Fruits That Keep Gelatin From Gelling

Other types of fruit contain proteases can also ruin gelatin. Examples include figs, fresh ginger root, papaya, mango, guava, pawpaw and kiwi fruit. The enzymes in these fruits aren't exactly the same as the ones in pineapple. For example, the protease in papaya is called papain and the enzyme in kiwi is called actinidin.

Adding any of these fresh fruits to gelatin will prevent the collagen fibers from forming a mesh, so the dessert doesn't set up. Fortunately, it's easy to deactivate the enzymes so they won't cause a problem.

Apply Heat to Use Pineapple

You can still use fresh fruit with gelatin, you just have to denature the protein molecules first by applying heat. The enzymes in bromelain are inactivated once they have been heated to about 158° F (70° Celsius), so while fresh pineapple prevents Jell-O from gelling, gelatin made using canned pineapple (which was heated during the canning process) won't ruin the dessert.

To denature the protein molecules, you can boil cut pieces of fruit in a small amount of water for a few minutes. A better way to preserve most of the fresh flavor and texture is to lightly steam the fruit. To steam fresh fruit, bring water to a boil. Set the fruit in a steamer or strainer over the boiling water so only the steam affects it. A third way to use the fresh fruit in gelatin is to mix it in with the boiling water used to make the dessert and give the hot water time to work its chemical magic before stirring in the gelatin mix.

Fruits That Don't Cause Problems

While some fruit contains proteases, many do not. You can use apples, oranges, strawberries, raspberries, blueberries, peaches, or plums without experiencing any problems.

Fun Experiments With Gelatin and Pineapples

If you'd like to learn more, experiment with different types of fruit to try to determine whether or not they contain proteases.

  • See what happens if you freeze pineapple or mango. Does freezing deactivate the enzymes?
  • Try mixing in a teaspoon of meat tenderizer with gelatin. Does it set up?
  • See what happens if you sprinkle meat tenderizer on gelatin after it has already set. Alternatively, see what happens if you place a fresh slice of pineapple on top of gelatin.
  • What other processes or chemicals denature collagen in gelatin so it won't set up?
  • What happens if you use a different chemical that gels instead of gelatin? For example, gel desserts and treats may also be made using agar.