Why does cereal go Snap, Crackle and Pop!?

19 July 2009

Question

Hello, Naked Scientists, could you please tell me what's happening when you hear the snap, crackle and pop with Rice Crispies? Thank you.

Answer

We put this to Paul Wheeler:Hi my name is Paul Wheeler and I work for Kelloggs.It's actually a really simple processes it's got a lot to do with compression. What we do is we take little grains of rice. We soak them in water, add our secret ingredient to it and then we cook the rice at a really high temperature. What happens then is the rice puffs up and little air pockets form inside the grains of rice. Now also when you cook this kind of thing, rice, at such high temperature the starch molecules kind of begin to bond together and what that does is if you were to take a rice crispie out of the packet and look at it under a microscope. You would see the actual surface of the rice becomes more brittle and actually more transparent. So what happens is when you pour the cold liquid onto the rice crispie the small bubbles of air that we've got, they collapse in on themselves and the rice that's crisped up through the cooking process collapses as well and that's where you get the sound-effect from, your listeners will hear when they pour their milk on their cereal. Its a really, really a simple process and actually people looked at the surface of the milk when that's happening they can actually see the air bubbles rise up and appear.

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