Flavoured gelatin desserts have been made since the early 19th century, but required a great deal of work to clarify the gelatin and prepare it for use. The advent of Jell-O, around the turn of the 20th century, made gelatin desserts quick and easy enough for any home cook to undertake. Jell-O makes approximately a 3 per cent gelatin solution, enough gelatin to keep it firm in refrigeration or for a shorter time at room temperature. However, gelatin softens and melts at 35 degrees Celsius, so care must be taken on hot days.
Keep Jell-O in the refrigerator until it is served. This is also advisable from a food safety standpoint, since gelatin desserts are prone to spoilage, like other forms of protein.
Serve the Jell-O in frosted or refrigerated dishes, when possible, or on a chilled platter. The dishes or platter will slow the warming process.
Cool the Jell-O slowly, when it is first made. Slow cooling allows the gelatin molecules to form a stronger bond, which will also inhibit melting.
Add extra gelatin. Reinforcing the Jell-O with a small quantity of unflavored gelatin will make a stronger gel, which will resist melting.
Replace a portion of the water with alcohol, when you are making the Jell-O. Replacing one tbsp of water in each cup with vodka or white rum will help the Jell-O form stronger molecular bonds, which will help slow melting. Do not use this method if the Jell-O is to be served to children.
If refrigeration is not available, store the Jell-O in a picnic cooler with several frozen gel packs for chilling.