The Science Behind Pop Rocks Candy

published Oct 23, 2015
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(Image credit: frankieleon)

I’m pretty sure that Pop Rocks ranked quite high as one of the most entertaining candies of your childhood. A fizzy, popping feeling of tiny bubbles exploding, accompanied by their signature crackling sound when they hit your tongue – even your friends could hear them pop and fizz every time you opened your mouth. But where does the “pop” in Pop Rocks come from?

It’s Not a Carbon Dioxide-Forming Reaction

Just like with the Mentos-soda geyser, you might expect that the bubbles that pop and fizz come from a reaction occurring on your tongue when you pop a handful of Pop Rocks into your mouth, generating carbon dioxide, like when baking soda (sodium carbonate) reacts with an acid.

Once again, this is not the case. The carbon dioxide is already present in Pop Rocks, trapped within the rocks of candy.

How Pop Rocks Are Made

First, the ingredients (sugar, lactose, corn syrup, and flavors) are heated together and brought to a boil. Then the mixture is flushed with carbon dioxide, and as the candy cools, the carbon dioxide ends up trapped within as tiny bubbles. If the candy is kept in a cool, dry place, then it takes a while for the trapped carbon dioxide to escape. But if you pour Pop Rocks onto your tongue, the warm, humid environment will cause the candy to melt and dissolve, releasing the tiny bubbles of carbon dioxide into your mouth, along with an audible crackle sound and a fizzy, popping feeling.

Pop Rocks Aren’t the Only Popping Candy out There

There are other “popping” candies on the market, like Fizz Whizz and Lotsa Fizz, but they don’t all fizz for the same reasons. Check the ingredients: Lotsa Fizz candies contain sodium bicarbonate and tartaric acid in powder form, and as soon as the candy hits your tongue, those two components dissolve, allowing them to react to generate carbon dioxide and that fizzy feeling in your mouth.

So, while Pop Rocks already contain the carbon dioxide responsible for that popping sensation, other candies may rely on an acid-base reaction that happens when the candy hits your tongue.

What’s your favorite “popping” candy?