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  #1  
Old 06-19-2007, 11:29 AM
AskNott AskNott is offline
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Physics in the kitchen: How hot can boiling water get?

To avoid burning garlic, I don't add it until liquid is added to the sautéed veggies.

I believe (without any documentation) that boiling water will never exceed the boiling temperature of roughly 212° F. Is that really true? I realized the other day that I "knew" this without knowing for sure.
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  #2  
Old 06-19-2007, 11:33 AM
treis treis is offline
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It's basically true. The exact temperature will depend on the concentration of various salts and the atmospheric pressure at your location. However once the water is boiling it will remain at that temperature until all the water is boiled off.
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Old 06-19-2007, 11:38 AM
CookingWithGas CookingWithGas is offline
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Water at sea level doesn't exceed 212F because hotter than that it becomes steam. It is possible to superheat water under some conditions but I'm not sure what they are; those conditions would probably not occur in a kitchen sauté pan.

At higher pressure, water will get hotter than that before it boils. If you add enough salt you will notice the water will get hotter, but that's more salt than would be used in cooking.

On cross examination, why are you adding liquid to sautéed vegetables? I always add the garlic last, sauté it until it is fragrant, and then remove from heat before it browns. Cooking garlic in liquid produces a differentmore subtle, result.
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Old 06-19-2007, 12:21 PM
recessiveMeme recessiveMeme is offline
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It doesn't necessarily have much to do with traditional cooking, but I've been led to believe that microwave ovens can "superheat" water such that the water temperature exceeds its normal boiling point without actually boiling. I don't know what the theoretical upper limit on that sort of thing is though. Snopes mentions the phenomenon here but doesn't go so far as to speculate.

Anyhoo... apparently water in this state can spontaneously boil. Just a WAG on my part, but it seems like in so doing, it would return to a "normal" boiling temperature eventually. If that is the case, I guess it'd be boiling above boiling temperature for some non-zero amount of time.

'Course, I'm making most of that up so I could be completely wrong.
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Old 06-19-2007, 01:03 PM
si_blakely si_blakely is offline
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Quote:
Originally Posted by recessiveMeme
It doesn't necessarily have much to do with traditional cooking, but I've been led to believe that microwave ovens can "superheat" water such that the water temperature exceeds its normal boiling point without actually boiling. I don't know what the theoretical upper limit on that sort of thing is though. Snopes mentions the phenomenon here but doesn't go so far as to speculate.

Anyhoo... apparently water in this state can spontaneously boil.
How about spontaneously explode. Superheated water is really dangerous - a large percentage of the water can turn to steam and propel the remaining boiling water everywhere.

How do you think geysers throw water so high?

Si
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  #6  
Old 06-19-2007, 01:13 PM
FlyingCowOfDoom FlyingCowOfDoom is offline
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Quote:
Originally Posted by recessiveMeme
It doesn't necessarily have much to do with traditional cooking, but I've been led to believe that microwave ovens can "superheat" water such that the water temperature exceeds its normal boiling point without actually boiling. I don't know what the theoretical upper limit on that sort of thing is though. Snopes mentions the phenomenon here but doesn't go so far as to speculate.

Anyhoo... apparently water in this state can spontaneously boil. Just a WAG on my part, but it seems like in so doing, it would return to a "normal" boiling temperature eventually. If that is the case, I guess it'd be boiling above boiling temperature for some non-zero amount of time.

'Course, I'm making most of that up so I could be completely wrong.
I've done this. If you have a very clean container and pure water, it is possible to superheat the water. Once superheated, the water will explode if it's disturbed. I think it has something to do with the fact that for the water to boil, the molecules have to move enough to shake free of their neighbors. When heating in the microwave, the molecules are heated but don't move enough to boil.

I think.

--FCOD
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  #7  
Old 06-19-2007, 01:49 PM
AskNott AskNott is offline
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Quote:
Originally Posted by CookingWithGas
...
On cross examination, why are you adding liquid to sautéed vegetables? I always add the garlic last, sauté it until it is fragrant, and then remove from heat before it browns. Cooking garlic in liquid produces a differentmore subtle, result.
For sauces, of course! In my kitchen, the liquid is usually accompanied by diced tomatoes. Other times, the liquid is water or white wine to deglaze the lovely stuff on the pan. I'll stop, before I wax poetic about sauces.

For Flying Cow Of Doom:
From what I've read about superheated water, it has to do with the need for something for the start of a bubble to form around. Often, it's a flaw in the surface of the glass. Alton Brown suggests putting a wooden skewer in the vessel before microwaving, to act as a bubble node.

Anyway, thanks, everybody.
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Last edited by AskNott; 06-19-2007 at 01:51 PM..
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Old 06-19-2007, 02:07 PM
asterion asterion is online now
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Quote:
Originally Posted by AskNott
For Flying Cow Of Doom:
From what I've read about superheated water, it has to do with the need for something for the start of a bubble to form around. Often, it's a flaw in the surface of the glass. Alton Brown suggests putting a wooden skewer in the vessel before microwaving, to act as a bubble node.
Pretty much. Without a nucleating point, bad things can happen. That's one reason chemists use boiling stones, so that the bubbles have places to form without everything "bumping."

Last edited by asterion; 06-19-2007 at 02:09 PM..
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  #9  
Old 06-19-2007, 02:18 PM
robby robby is offline
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Quote:
Originally Posted by FlyingCowOfDoom
I've done this. If you have a very clean container and pure water, it is possible to superheat the water. Once superheated, the water will explode if it's disturbed. I think it has something to do with the fact that for the water to boil, the molecules have to move enough to shake free of their neighbors. When heating in the microwave, the molecules are heated but don't move enough to boil.

I think.

--FCOD
Not exactly. A container of water needs a "nucleation site" to begin bulk boiling. This could be anything from suspended contaminants in the water to scratches inside the container. If no nucleation sites are present, it's possible to superheat the water. At some point, a tipping point will be reached and boiling will begin. If the water is sufficiently superheated, this can be a dramatic occurrence, as a significant proportion of the water in the container flashes into steam nearly instantaneously.

By definition, the average kinetic energy of the water molecules is proportional to the temperature of the water, so superheating doesn't have anything to do with the molecules "not moving enough."

And back to the OP--to add on to what others said, if water is under high pressure, liquid water can get very hot indeed without boiling. In a typical pressurized-water nuclear power plant, the liquid water used as primary coolant is under a pressure of around 2000 psig, and a temperature of nearly 500 deg F! Like any other superheated liquid water, if the water is vented from the primary coolant piping, it instantly flashes into steam. This can be a problem, if you have a pipe rupture.

Last edited by robby; 06-19-2007 at 02:20 PM..
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  #10  
Old 06-19-2007, 04:36 PM
gigi gigi is offline
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Quote:
Originally Posted by si_blakely
How do you think geysers throw water so high?
They exit through a tiny hole and spray like a pimple does? Yes, I'm serious.
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