How is popping candy made?

Popping candy is hard candy with bubbles of carbon dioxide trapped inside it under pressure. When it dissolves on your tongue, the bubbles burst with a crackle: see how does popping candy pop? Making it means doing something unusual: setting a sugar syrup while it is under very high gas pressure.

The classic method

As described in a patent from 1980:

1. Boil. Sugars are dissolved in water and boiled at about 160°C until only 3 per cent of the mixture is water.
2. Cool a little. The syrup is cooled to about 138°C.
3. Gas it. While it is stirred hard, it is pressurised with carbon dioxide at about 730 pounds per square inch, around 50 times normal air pressure.
4. Set under pressure. It is kept under pressure while it cools and sets, trapping the gas in bubbles, most of them 225 to 350 micrometres across.
5. Release. When the pressure is finally released, the solid candy shatters into pieces of different sizes.

That shattering is why popping candy comes as small, uneven crystals rather than neat sweets.

A newer way to make shaped pieces

A patent by the inventor Tolga Erden, first filed in 2010, describes a way to make popping candy in shapes. The candy mass is first gassed with carbon dioxide while it is mixed, then pulled into a cord, cut to size and set into trays with mould cavities. The trays go into a pressurised reactor, where carbon dioxide is injected at 1 to 150 bar for 1 to 15 minutes, and the candy is cooled to room temperature and hardens. Splitting the job into stages means the machinery can be reached while it is running without losing the gas, which the older method, with the whole system under pressure, did not allow.

Keeping the pop in chocolate

Popping candy is also mixed into chocolate, as in Cadbury's Marvellous Creations, and that brings a problem. A patent filed in 1979 by the Italian chocolate maker Perugina explains that moisture in the chocolate tends to soak into the candy, which swells and loses its gas pressure, so the popping fades or stops. The answer is dry chocolate, with a moisture content between 0.1 and 5 per cent and preferably below 1 per cent. The same patent describes stirring the candy into the chocolate in a machine heated to about 35°C, at between nine and eight parts chocolate to one or two parts candy, using crystals sifted to between 0.5 and 4 mm. The candy itself holds only about 0.1 to 1 per cent carbon dioxide by weight, ideally 0.4 per cent.

Who makes it

The idea was first patented by the General Foods chemists Leon Kremzner and William Mitchell in 1961, and Pop Rocks went on sale in the United States in 1976. Today the brand belongs to Zeta Espacial of Barcelona, which also sells popping candy as Peta Zetas, Wiz Fizz and Magic Gum. A powdered cousin, once sold as Space Dust, was also made by General Foods: see Space Dust

Allergens

Pop Rocks are made from sugar, lactose, which is milk sugar, and flavouring, so check any popping candy for milk: see milk in sweets

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