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How Rice Expands: Growing Grains
There’s more going on in a bed of rice than meets the eye. Zoom into its surprising microscopic structure with Groupon’s close-up look.
A typical recipe on the back of a rice package might go like this: add one cup of rice to two cups of water and simmer it until it’s tender and steaming. You’ll also have to make sure you leave some room at the top of the pot for the rice to expand—which is a little surprising when you think about it. Sure, the water is absorbed into the grains of rice, but you’ll typically end up with rice that’s greater in volume than the volume of both its components. And it’s not as if this happens with every food you toss in boiling water: think of noodles, or broccoli.
What’s going on here? Put simply, rice doesn’t just absorb water like a sponge. Instead, a complex rearrangement of molecules makes the starch in the rice change structure and actually take up more space, much as a suitcase does when placed in an airplane’s overhead bin. Inside each uncooked grain is a three-dimensional lattice of starch molecules that makes the grain tough and mostly impervious to water. But bring the water to a boil, and this all changes: the starch molecules themselves swell and eventually burst, losing that neatly stacked structure in the process. When that happens, amylose, one of the previously water-fearing chains of sugars that make up each starch molecule, escapes into the surrounding space and takes on a structure that itself holds water.
You can imagine each of these elements as a thread in a sweater: normally it lies flat, but start pulling out the threads and instead of a sweater you’ll end up with a much larger heap of knots and tangles perfect for a kitten’s prom dress. Because the molecules go from a neat arrangement to a complicated mass, the rice itself expands more than it would if it were simply full of water.