How does popping candy pop?

Popping candy crackles on your tongue. It is not a chemical reaction like sherbet. The pops come from gas that was forced into the candy when it was made, and that has been waiting inside ever since.

Gas trapped in sugar

Popping candy is a kind of hard candy with tiny bubbles of carbon dioxide sealed inside it under pressure. When the candy dissolves in your mouth, the bubbles are released, and each one lets go with a small pop. Lots of them going off together make the crackle.

How it is made

A patent from 1980 describes the method. Sugars are dissolved in water and boiled at about 160 degrees Celsius until only 3 per cent of the mixture is water. The mixture is cooled to about 138 degrees and, while it is stirred hard, it is pressurised with carbon dioxide at about 730 pounds per square inch, around 50 times normal air pressure. It is kept under that pressure while it cools and sets, trapping the gas in bubbles, most of them between 225 and 350 micrometres across.

When the pressure is finally released, the solid candy shatters into pieces of different sizes. That is why popping candy comes as small, uneven pieces rather than neat sweets.

One brand, Pop Rocks, is made of sugar, lactose, which is milk sugar, and flavouring, as well as the gas.

Who invented it

The idea was patented by two chemists at General Foods, Leon Kremzner and William Mitchell, in December 1961. General Foods first tested Pop Rocks in Canada in 1974 and launched them in the United States in 1976. They were an immediate hit, at one point outselling other sweets by as much as ten to one. A powdered version, sold as Space Dust, was also made by General Foods: see Space Dust

The exploding stomach myth

Popping candy's success was dented by a rumour that eating it with a fizzy drink would make your stomach explode. One version claimed a child actor from a cereal advert had died that way. It was false. General Foods ran newspaper advertisements in 1979 to reassure parents and sent the inventor on the road to explain that a packet of Pop Rocks contains less gas than half a can of fizzy drink.

The rumour still hurt sales. Production stopped in 1980 and the candy was off the market until 1986. Decades later, on the very first episode of MythBusters, the presenters filled a pig's stomach with six packets of Pop Rocks and six cans of cola, plus acid to match a real stomach. It swelled to three times its size but did not burst.

Popping candy and sherbet

Popping candy and sherbet both tingle, but in different ways. Sherbet fizzes because it contains an acid and a base that react when they get wet, making gas on your tongue. Popping candy makes no new gas at all; it simply lets out the gas that was packed into it: see why do fizzy sweets fizz on your tongue?

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