How does popping candy work?

Popping candy or pop rocks is a strange sort of children's sweet which seems to explode inside your mouth we try to investigate what is going on.

What you need

What to Do

What may Happen

You should find that all the approaches cause the rocks to explode.

What is going on?

There are a couple of ways that popping candy may work, the most obvious would be some kind of chemical reaction between and acid and a carbonate which gives off carbon-dioxide, like sherbert. Although the water experiment is consistent with this, the explosions produced by breaking the rocks indicate that it is the wrong explanation.

What is actually going on is that the popping candy is made by mixing sugars (sucrose and lactose, and some flavouring) then heating them up until they melt. This molten mixture is exposed to very high pressure carbon-dioxide at a pressure about 40 times greater than atmospheric ( 600psi ). Lots of carbon-dioxide then dissolves in the sugar. The mixture is then cooled to room temperature and the pressure is dropped.

At which point all the dissolved carbon-dioxide wants to escape, and forms bubbles, just like when you open the lid of a bottle of fizzy drink. But in this case the sugar is solidifying, so the high pressure larger bubbles shatter the sugar into small lumps or rocks.

The small bubbles are preserved still at an enormous pressure, and when you break the sugar mechanically, or weaken it by dissolving the outer layers, the bubbles explode, providing that 'unique' popping experience.

Written by Dave Ansell