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I couldn't think of a better title because I'm not sure what's going on with this phenomenon--someone who has an answer, please edit to fit this better.

I noticed that when I cook rice, at some point after most of the water has evaporated and the rice is settled at the bottom of the pot, there is a "lattice" of regularly-spaced gaps in how the grains at the top are arranged, with the holes extending down a grain or two.

I can try to explain this better if it doesn't make sense, but for now I can't do much better because it mystifies me. What's up here?

(Better tag suggestions are also welcome...)

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Huh, I might have to cook some rice to see this effect in action ;-) I can't think of a physical explanation off the top of my head, but let's see what people come up with. –  David Z Jan 16 '11 at 7:02
    
@David: that effect is definitely rice dependent. Although I've seen it a few times, usually nothing out of ordinary happens. In any case, I have no idea what's causing it. –  Marek Jan 16 '11 at 8:12

1 Answer 1

as rice cooks it releases starch. When the water level falls below the rice, the steam that is expelled creates the gaps that you noticed.

These gaps are not, in fact regularly distributed. They are in random positions and with random orientation. They do have a regular size corresponding to a grain of rice.

The reason is easy to grasp - the steam being released has a dropping pressure (the less water, the less steam being released). So what happens is that the gaps get smaller and smaller and finally they will be as small as possible, while being held in shape by the starch.

They also try to cover the whole surface, as steam is generated homogeneously and therefore has no preferred areas of the surface to generate these holes.

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Do you also have any explanation for why this doesn't always happen (based on my very subjective observation)? Perhaps it depends on the precise way rice was cooked? –  Marek Jan 16 '11 at 11:53
    
It always happens when rice is cooked oriental-style (i.e. rice covered by cold water left to boil undisturbed). In my experience it happens consistently, so I don't know any better... –  Sklivvz Jan 16 '11 at 11:57

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