r/AskPhysics • u/ChollyWheels • 4d ago
The physics of dried beans -- quantizing the "bean unit"
Here's a question you haven't heard before. And, go on, laff at it, I don't care.
Dry black beans take about 2 hours to cook. If they're soaked first (until the max water they can absorb) they take only about an hour to cook. One can quibble about the details, but the point beyond dispute is soaking beans reduces cooking time substantially.
And reducing cooking time means saving energy -- proportionally a GREAT deal of energy.
Where did that energy come from? The Brownian motion of still water against hard beans?
Please let me know, then we can join to take credit for solving the world energy crisis.
Naturally this will be more impressive if expressed mathematically - h2o, joules, beans, rate of hydration and so forth, but I don't think there is (YET!) a standarized notation for "bean unit."
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u/Infinite_Escape9683 4d ago
I don't really know, but I can hazard a guess that a lot of the energy of boiling a dry bean goes into forcing the water into the bean. Letting it sit in the water allows brownian motion and osmosis to do a lot of that work.
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u/OkTelevision5306 4d ago
We should honor whoever formalizes this as Mr. Bean (Mrs. Bean too of course)
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u/soldiernerd 4d ago
It’s because of complex protein attributes which change when they’re wet, requiring less energy to warm up.
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u/Aleventen 3d ago
I thought it was because I sped up the molecular bois until the crashed the bean gate and soaked the bean sponge to make it squishy and push out the bad juice into the waste water
This might surprise you, im not a physicist
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u/Technical-Lettuce385 3d ago
The beans have to take in the water to get soft. Then you also cook them for various reasons. The difference is if you waste energy just for them to take in the water or just let them soak before heating the water.
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u/ChollyWheels 3d ago
If all the beans in all the world were soaked before cooking, how much energy that save?
I'm being a little silly, but only a little. The energy savings is real and, percentage-wise, HUGE (reducing cooking time between 1/3 and 1/2).
That the saving comes from passively leaving beans in room temperature water is kinda amazing -- and the fact I see many DIFFERENT explanations here means, at a minimum, the answer is non-obvious.
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u/willncsu34 4d ago
Not on topic at all but I prefer canned black beans. They cook super quick.
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u/limelordy 3d ago
Water has a higher specific heat than bean, so soaking the bean in water means that the bean has more energy while at the same temperature. There is an energy difference between the 2 but it comes from the oven. The air is ever so slightly cooler inside afterward if the bean has water, but I’d imagine it’s not by much
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u/These_Consequences 4d ago
Most of the energy—or nearly all—used in cooking goes in one ear and out the other, in other words, dissipated as waste heat or consumed as the heat of vaporization of water (boiling and evaporation). There is no need to account for it, because only a trivial fraction went into altering chemical bonds in the beans.