FOR ME, THE MOST ASTONISHING THING ABOUT THIS MECHANISM IS THAT SO MUCH SOUND GETS OUT
It’s one of those sounds that’s so familiar, we’ve almost forgotten to hear it. You pour milk on to your Rice Krispies and immediately there’s a jolly, crackling noise that sounds like a log fire with the volume turned down, or perhaps like mice running around on tiny bubble wrap. It would be completely weird if we weren’t so used to it – how can starch so fragile that it’s barely there make such a loud noise? I was set the task of finding out.
Each little Rice Krispie has the structure of a sponge. If you cut one in half, you can see that it’s full of tiny air pockets surrounded by very thin walls. Sometimes the starch walls are so thin that they’re transparent, and quite often the outside of a Rice Krispie has got holes in it where an expanding bubble of gas on the inside burst through. The walls are made of a mixture of long carbohydrate molecules (that’s the starch) and sugar, and together they form a material a bit like a glass. It’s brittle, so if you crush it, you hear sharp snaps as the thin layers shatter. That makes sense when it’s dry, but surely wet starch is soggy, and is much more likely to squish than shatter!
There’s quite a lot of variety in the popping sound that you get. If you try putting water rather than milk on your Rice Krispies, the crackling is loud and immediate. And you can see bubbles of air being expelled from the insides of the cereal. Skimmed milk produces quieter crackling than water, and full fat milk is quieter still. I also tried different temperatures, and found that hot milk is much noisier than cold milk.
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