How to Make Glowing Jelly

Here’s a really simple and fun experiment to do at home: make glowing jelly (or jello, American friends)! The method is really easy - you’re just making jelly - but you do need some kind of UV light source to see the effects[1].

It’s a very simple idea: you make jelly but use a 1:1 mixture of plain ol’ water and tonic water (e.g. Canada Dry). Tonic water contains quinine which is naturally fluorescent and so the resultant jelly will glow under a UV light. Here’s what I did:

1. Boil 100ml of water and mix with the jelly so it all dissolves.
2. Top up with cold water up to 300ml.
3. Add 300ml of tonic water.
4. Mix it up really well and put it in the fridge.

Quinine glows a blue-ish colour under UV light so I used green jelly to maximise the effect. I’m assuming that the jelly acts as a kind of filter to the fluorescence, so using red jelly would probably result in a very poor glowing jelly. And nobody wants that. There was no blue jelly in the shop; not much blue food in general, actually.

Fluorescence occurs in some materials when they absorb high-energy light photons and then re-emit that energy as lower-energy photons. In this case, the quinine is absorbing UV photons and re-emitting them as visible light (UV light is higher-energy than optical light).

The results were pretty much awesome. You can see our glowing green jelly above. It tasted great too. Lime turned out to be a good flavour to accompany the tonic water, which would normally have a bitter taste. The kids gobbled it up - under the glow of the UV lamp.

This project was really quick and easy and the kids loved it! I think there may be glowing jelly - and maybe other glowing foods - at Halloween this year.

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[1] You can buy UV torches and lights at Maplin or Amazon. There are likely other places too, of course :)