PHYSICS

What Makes Your Cereal Go Snap, Crackle, Pop?

Reported December 2006

MINNEAPOLIS (Ivanhoe Broadcast News) --

Snap, crackle, pop! Does your cereal talk to you? Rice Krispies -- the breakfast that talks to you -- has been around for nearly 80 years, but scientists have only recently figured out why it makes that noise.

Food scientist Ted Labuza, Ph.D., says there are a few reasons.

"Rice Krispies has sugar in it. It's the sugar that causes it to interact in the different way with the starch, and that makes a big difference," Dr. Labuza, who is professor of Food Science and Engineering at University of Minnesota in Minneapolis, tells Ivanhoe. In fact, sugar is the second ingredient in the Krispies. It's much lower on the list in other cereals.

Another reason? Rice Krispies are cooked at such a high temperature, the sugar forms crystals that behave almost like glass. If you crush them, they'll break into pieces.

During the cooking process, each piece of rice expands, and tiny air-filled caves form inside. The Krispies' bubbles are about 20-times bigger than those in puffed rice cereal.

Here's what really happens inside: The Krispie absorbs the milk and the air-filled caves become filled with liquid. Air is then pushed around until the walls shatter and make a noise. And that's what you hear!

Dr. Labuza says the Krispies probably make different sounds because of the different sizes of the air pockets. They stop making noise after they pick up all the milk they can handle. He says this is the only food that acts this way -- with the exception of Pop Rocks candy. But never mind why it happens. Some of us only care how it tastes!