I have a tendency to experiment in the kitchen and most of the time it goes well. One particular experiment involved adding fresh pineapple to jelly. It didn’t set.
It was a disaster. I was making a tropical fruit inspired trifle. I was so incredibly confident of my predicted success that I had talked up this dessert and even incorporated components from some of the people attending. Instead of having set jelly to layer in amongst layers of cake and fruit, I had slush. I had three hours to make a replacement dessert. The pineapple slush was exiled to the back of the fridge while I frantically I made a pavlova covered in cream and tropical fruit.
After everyone had left and with the dishwasher whirring away, I brought out the bowl of pineapple slush. After 10 hours, it still had not properly set. I declared war on pineapple that night in the kitchen. I had to find out why the jelly hadn’t set. I was so annoyed because my stomach was looking forward to a tropical fruit trifle that never eventuated. Pavlova just wasn’t the same.
The reason why my pineapple jelly did not set and was not ever going to set despite the length of time spent in the fridge was because fresh pineapple contains an enzyme called bromelain. It is a plant extract that is usually used as a meat tenderiser. Jelly is made from gelatine which is made from the collagen found inside the skin and bones of animals. It is a common gelling agent in not just jelly but also in pharmaceuticals, marshmallows, photography and even found in some low-fat yoghurt.
Bromelain and other enzymes in the pineapple interfere with the preparation gelatine-based desserts because it breaks down the gelatine making it impossible for a wobbly jelly to form. This enzyme can be deactivated by heating the pineapple to a temperature above 65oC. A quick boil of fresh pineapple in either its own juices or water for a few minutes should suffice. Another alternative is to use canned pineapple where the heating processes before being canned has been high enough to deactivate the bromelain.
Other fruits to be wary of adding to jelly include fresh papaya and kiwi fruit. They also contain enzymes that interfere with the setting of jelly.