If you’ve ever tried to make fruit jellies, you might well be aware that not all fruits are up to the task. Pineapple, papaya, and kiwi are all impossible to make jelly out of if you’re using the raw fruits. This is because they all contain enzymes that are capable of breaking up gelling agents, and stopping the gel network from forming. You can still make pineapple, kiwi, and papaya-flavoured jelly, but you’ll need to use fruit that has been cooked (or tinned fruit) as this denatures the enzymes and prevents them from interfering with the gel network.