It’s easy to make jam–just fruit, sugar and cook until thick. You don’t have to worry much about it–it can be a little dense or a little runny, but it still spreads. Jelly is a different thing entirely; you have to get the timing just right or you have syrup or cement. With jelly, an alchemical change takes place, which is nowhere more dramatic than with pineapple guavas.
But after it boils up over 200 degrees, it transforms. In the bubble and seethe, it changes to a clear pinkish gold liquid.