Candy Can Be a Gas!

Lollipops and most other forms of hard candy are made from one basic recipe: sugar, corn syrup, and flavoring. The ingredients are heated at high temperatures to obtain a pure sugar syrup, which turns into hard candy when left to cool. No wonder they taste so sweet!

However, by adding one extra ingredient, you can really shake things up and make hard candy do some pretty neat things—like explode!

If you've ever popped Pop Rocks, you've felt the familiar fizzle, snap, crackle, and pop of candy granules erupting on your tongue. So what makes the candy take on a life of its own when you put it in your mouth?

The secret ingredient—which isn't really secret, since it's written right there on the package—is carbon dioxide gas. According to Marta Mas, marketing director of Pop Rocks, Inc., this is how it works.

The hard candy recipe ingredients are heated until all the sugar has melted. The liquid is then boiled until it reaches 300 degrees F (149 degrees C). When the pure sugar syrup is gasified with carbon dioxide at the super-atmospheric pressure of about 600 psi (pounds per square inch), tiny gas bubbles form inside it. This mixture is then left to cool and solidify while it is maintained under pressure. Once the mixture has solidified, the exterior pressure is released. The result is that the pressure inside the candy is greater than outside, which causes the interior pressure to fracture the sugary mass into granules. That's why Pop Rocks are in fragmented form.

If you take a look under a microscope, you'll see that the granules are still filled with high-pressure bubbles. When you pop the rocks into your mouth, the bubbles are released, making popping sounds as the candy melts. Tasty pressure!

Vocabulary

atmospheric pressure:
Pressure caused by the weight of the atmosphere. At sea level it has a mean value of one atmosphere but reduces with increasing altitude.

granule:
A small, hard grain, as of sand, salt, or ice.

mixture:
Matter made up of two or more substances or materials that are physically combined.

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Activity

  1. What physical change releases carbon dioxide gas from Pop Rocks?
  2. Why is carbon dioxide gas used in making Pop Rocks?
  3. Think of another food product that contains carbon dioxide gas. Why is carbon dioxide gas used in this food product? What happens to the carbon dioxide gas as the product is consumed? Write a sentence or two describing the food product and the role of carbon dioxide gas in it.