What causes that characteristic crackle?

Popping candy is a treat and a science experiment all in one, but ever wondered what makes it crackle? Picture: Shutterstock.
Popping candy is a treat and a science experiment all in one, but ever wondered what makes it crackle? Picture: Shutterstock.

Reader Jennifer asked: What causes that characteristic popping candy crackle?

If you've upped your lolly intake over the past few weeks (we certainly have at Cosmos), you may have tried some popping candy.

It's a treat and a science experiment all in one, causing a tingling sensation on the tongue and a delightful crackle as you eat it.

But what causes that popping sensation?

You might think it's a chemical reaction, but it's actually a pretty cool combination of gases and heat.

Precise recipes vary from brand to brand, but popping candy is typically a mixture of a few different types of sugar, and tiny pressurised bubbles of a gas, usually carbon dioxide.

For this reason, it's also referred to as "gasified candy" in some patent applications.

The gas is added to sugar at a high pressure - at least two or three times typical air pressure at sea level, and sometimes much higher.

With the right combination of temperature and pressure, the sugar forms small crystals, each containing several gas bubbles roughly a 10th to a fifth of a millimetre in diameter.

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Sugar dissolves in water, so when the candy makes contact with your tongue, the water in your saliva breaks up these bubbles.

The pressurised gas escapes, sometimes with enough force to crack the rest of the candy crystal. This is what causes the tingling, popping sensation.

Both the bubbles and the crystals are very small, so the amount of force involved in these cracks is unlikely to cause any problems.

Popping candy is typically a mixture of sugar and tiny pressurised bubbles of a gas, usually carbon dioxide. Picture: Shutterstock.

Popping candy is typically a mixture of sugar and tiny pressurised bubbles of a gas, usually carbon dioxide. Picture: Shutterstock.

But in a small amount of bad news, at least one lab-based study has found that popping candy can have an effect on tooth enamel.

If you want to watch gasified candy pop but are concerned about your teeth, you can add it to plain water instead - this will also set it off.

This is particularly good news, because it means that popping candy can be used in chemical reactions.

Last year, a group of Chinese and Australian chemists used popping candy to extract some key molecules from vinegar and two alcoholic drinks: beer and Baijiu, a liquor made from fermented grain. This opens the way for a range of potential applications in pharmaceutical or food additive manufacture.

The carbon dioxide released by the popping candy proved to be the perfect way to agitate the mixtures and disperse the relevant substances. And, because it uses edible sugars, the method is more environmentally conscious, and leaves the ingredients safe to ingest at the end.

  • These articles are published in partnership with Cosmos Magazine. Cosmos is produced by The Royal Institution of Australia.

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