I recall when the only caution against fresh fruit on the jello package instructions was pineapple. But these days supermarkets routinely carry fruits grandma never heard of, and many of them can't be used fresh in jello. I would love to use kiwi and melon in jello molds but they'd lose their shape when cooked. Does anyone know at what temperature the problem enzymes are deactivated? I am wondering if using less heat - brief steaming or baking perhaps - would be enough.