Question

There's a candy called "Pop Rocks". When you put it in your mouth it makes a loud popping sound and it feels amazing! How do Pop Rocks work?

Answer

"Pop Rocks" is an extremely cool candy to some people, but to other people it is just plain weird and they won't touch the stuff. Whether you are for or against Pop Rocks, you have to admit that it is definitely a technology candy - nothing in nature works like Pop Rocks do!

So how do they work? One of the amazing things about Pop Rocks is that they are patented! That means that you can go read the patent and see exactly how they work. The patent number is 4,289,794. You can click here to see the patent - This page is a synopsis, and if you click the View Images tag at the top of the page you can look at scanned images of the actual patent. Page 4 is the key page.

Here's the basic idea. Hard candy (like a lollypop or a Jolly Rancher) is made from sugar, corn syrup, water and flavoring (see this recipe for details on exact measurements). You heat the ingredients together and boil the mixture to drive off all of the water. Then you let the temperature rise. What you are left with is a pure sugar syrup at 300 or so degrees F. When it cools, you have hard candy.

To make Pop Rocks, the hot sugar mixture is allowed to mix with carbon dioxide gas at about 600 PSI. The carbon dioxide gas forms tiny, 600 PSI bubbles in the candy. Once it cools you release the pressure and the candy shatters, but the pieces still contain the high-pressure bubbles (look at a piece with a magnifying glass to see the bubbles). When you put the candy in your mouth, it melts (just like hard candy) and releases the bubbles with a loud POP! What you are hearing and feeling is the 600 PSI carbon dioxide gas being released from each bubble.

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