Preparing Jell-O sounds pretty straightforward: Mix the supplied gelatin with boiling water, add the appropriate amount of cold water, and place the mixture in the refrigerator to set for a few hours. But you’d be surprised—there are a lot of ways to mess up Jell-O, especially when additional ingredients like fruit are added to the recipe. Follow a few basic tips at the outset to make sure you get it right.
Make sure gelatin is completely dissolved in boiling water before adding cold water. If you add the cold water before the gelatin dissolves all the way, the Jell-O will not set properly.
Let Jell-O set in the refrigerator for at least six hours. If you pour it into thick molds or add fruits and vegetables, you should refrigerate it for even longer.
If you’re leaving Jell-O to set overnight, cover the pan with plastic wrap to prevent the Jell-O from hardening.
Let the Jell-O chill and thicken for 1 1/2 hours before adding fruits; then re-refrigerate for an additional four hours.
Make sure canned fruit and vegetables are well-drained before adding. Never use fresh or frozen guava, figs, ginger, papaya, pineapple, or kiwi, which all contain an enzyme that breaks down the gelatin and prevents it from setting properly.
When doubling the recipe, add twice the amount of gelatin and liquid—except lemon juice and vinegar. Salt, lemon juice, and vinegar should be added at 1 1/2 times the original recipe.