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When I cook things, such as scallop and salmon, I found that the food may be more tender if I wait till the water boils (at 100 C) and immediately turn the fire lower so that the water is not bubbling in the cook pot and maintain the fire at this level. But I noticed that at this point, there is more steam coming out of the water surface and the steam is far more visible than before.

I think I even test to see if there are in fact more steam by putting the my palm about 12 inches above the cook pot, and verified that in fact, when the fire is at high, there is less steam, but at low, there is more steam. Is there a physics principle that can explain this?

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3 Answers

I have been boiling water in our house for humidity at times during the cold weather. I noticed this phenomenon, but never with any food involved. I suspect it has more to do with the rapidity of which the matter is getting excited gives it less time to make the physical change. When the application of heat/energy is decreased, the fervent movement of the matter involved slows and the process of transformation is easier...the principle of dispersion lends to the water then spreading its energy to the surrounding environment in an accelerated manner vs the matter in question dealing with taking on the energy.

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I tried the experiment with a pot and 5mm of water and with a pan and 5mm of water. When it is just water steam at boiling is proportional to the fire as more bubbles form at the bottom of the pan and turn to steam.

So it must be the combined effect of food and water.

I suspect:

The surface of the scallops or salmon, if the heat is high, dries up fast and no longer evaporates, while it obstructs/absorbs the steam coming from the bottom where food touches it. In other words the food is seared immediately and less evaporative surface is exposed to air when heat is high.

When heat is low the fish does not dry up and gives off steam too, plus the fractal effect of the increased surface area, since no food is flat, must contribute to more steam at low fire.

A third effect might come from the bubble formation in the exposed surface of the liquid, since it will no longer be pure water. It might be that bubbles can be bigger and gather more steam before they burst, in the exposed to air part of the liquid, while for high heat they have too much energy and burst before accumulating steam. Again a food effect.

I will verify this supposition next time I braise salmon with teriyaki sauce.

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Once an experimental physicist, always an experimental physicist –  twistor59 Dec 31 '12 at 7:54
    
@twistor59 right :) . You have to start young . –  anna v Dec 31 '12 at 7:54
    
+1 :-) I'm currently staying at my mother's house and she disapproves of me using her kitchenware for Physics experiments. In any case, my mother tells me you should always put a lid on the pan when simmering! –  John Rennie Dec 31 '12 at 8:05
    
by the way, I suspect that even just water will have the same effect, as I remember just boiling some water in the cook pot and turn down the fire to lower level and keep it there, and steam came out a lot more than if fire was at high level –  動靜能量 Jan 3 '13 at 14:49
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We know that we see steam visually observe steam when water vapor condenses into water. Otherwise water vapor is transparent.My suspicion is that in the case when the fire is lower then the bubbling threshold, water vapour condenses into stream more easily. –  Prathyush Jan 28 '13 at 6:08
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I must admit that I have never noticed this, and indeed it runs somewhat contrary to what I would expect.

It's a suggestion rather than an answer, but when the heat is high there will be a strong updraught of hot air so is it possible that the steam is being carried away from the pan before it has a chance to condense to water droplets? Indeed if the air flow is fast enough the steam might never condense because it would be diluted into the surrounding air before droplet nucleation happened.

By contrast at very low heat the air flow around the pan is slow so the water vapour has plenty of time to condense and form visible droplets.

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protected by Qmechanic Jan 28 '13 at 5:28

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