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Once water is boiling you can either leave the heat on quite high, or turn it down a bit so that it just keeps boiling. Apart from extra water vaporating, does this have any effect on the taste of food you're boiling (meat, vegetables, eggs, etc.)?

With just common sense we could get to the following reasoning:

  • The liquid water is max 100°C (right?), beyond that it should vaporize (right?)
  • Water vapor could be hotter than 100°C (but how much, in normal cooking conditions?)
  • When boiling water, the vapor originates at the bottom of the pan
  • So technically the foot could be "hit" by this vapor, thus being heated above 100°C

Even if the above reasoning is correct, the questions would still be: would it matter how much you heat boiling water beyond 100°C? Can you significantly change the taste of boiled food by "boiling it really hard" or "boiling it slowly"?

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Just thought I'd point out that water (and other liquid) boils because of pressure, which rises with temperature. If you put water in a sealed box, pump air into it until the pressure rises higher, and then raise the temperature, it will boil at a higher temperature. –  annonymously Oct 11 '12 at 22:21
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You don't even have to pump air in--the evaporating steam will work fine. This is how pressure cookers work. –  zebediah49 Oct 13 '12 at 7:39
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6 Answers 6

There is a difference between a full rolling boil and a slow boil, but it's not really what you're suggesting. At a rolling boil, the water is mixing well enough that effectively it's all at 100°C. At a slow boil, it's really only boiling at the bottom, with bubbles floating up from there, so most of the water is actually a bit below 100°C.

This difference is pretty definitely bigger than any effect from steam coming into contact with food; the heat capacity of water substantially greater than that of steam, and the food will be in contact with water more of the time than steam anyway.

Finally, the bottom of the pan is substantially hotter than the water, and if you've turned the stove up higher to make it boil faster, it'll be even hotter, so food that comes into contact with it will cook (or more likely, scorch) faster.

So yes, things do cook faster at a rolling boil (what you call "boiling it really hard"), but it's not because of steam coming into contact with the food.

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I doubt that the sides or bottom inside of a pan of boiling water is significantly hotter than the boiling water. You can witness this yourself by viewing YouTube videos of water being boiled in paper cups and plastic water bottles.The water keeps the surface at boiling temperature. –  Jim Oct 11 '12 at 23:59
    
@Jim I doubt those paper cups and plastic bottles were boiled on a stove. It's completely possible to burn things on the bottom of a pot full of water (or soup, or sauce). –  Jefromi Oct 12 '12 at 1:51
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I found the phrasing "pretty definitely bigger" somewhat confusing. –  JYelton Oct 12 '12 at 15:23
    
@JYelton It sounds completely normal to me, but I guess we're not from the same place. –  Jefromi Oct 12 '12 at 17:10
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At a normal atmospheric pressure, even the steam created by boiling will only be 100°C. However, you will have to worry about the food touching the bottom part of the pan, as that can, and will, get hotter than the water.

So if what you're boiling is suspended or floating then no, it won't be any different.

I figure it's also worth mentioning that if what you're boiling is sensitive to movement (like poaching an egg), then a more rapid boil can effect the structure due to larger, faster, "more violent" bubbles. I don't think it would change the flavor at all though.

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In my experience, the most likely impact of a gentle boil vs. a furious rolling boil is going to be on texture of starchy foods, such as potatoes or other root vegetables, rather than flavor.

I've found that a gentle simmer of potatoes will result in a mostly intact shape and consistent texture, whereas an aggressive boil without perfect timing can result in the outer layers of the potato breaking apart, sometimes before the center has time to cook fully.

I've seen similar issues with stuffed parcels of pasta like ravioli or boiled won tons. I've also found that open pot egg poached eggs have much nicer results with a gentle simmer than an aggressive boil, perhaps for related reasons.

Since part of how we experience taste is texture, you could say that the "taste" is affected.

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I can't believe no one else mentioned this or voted this answer up ... and you end up with the excess starch in the water, which can cause other problems (eg. the boil over common in pasta, working back in the protein scum that forms when making stock before you can skim it off) –  Joe Oct 12 '12 at 3:22
    
not to mention that a "hard fast boil" can still dehydrate something like a protein and make it dry and mealy if the cook time isn't sufficiently long enough to tenderize the meat –  Brendan Dec 5 '12 at 19:54
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Point one: No, you can't significantly change the taste of food by choosing different boiling temperatures.

The taste of food depends on the final temperature it reaches. There are certain "turning points" for different types of food. Actin and myosin (the proteins in meat) curdle in the 60°C to 65°C interval for land animals, lower for fish. Different egg proteins curdle in the 50°C to 85°C interval, maybe a bit more, but not above 100°C. Collagen needs at least 68°C to melt, and starches need at least 70°C, depending on the source, but none of them needs above 100°C. All interesting changes happen within an interval below 100°C.

You can change the taste by slow heating, because heat travels by conduction through the food. If you heat a piece of meat at 100°C and wait until the middle has reached 62°C (well done), the outside surface will have reached 100°C and be dry. If you heat it at 62°C (for enough time that even the middle reaches them), the meat will be tasty throughout. The question is whether parts of the food are heated above a limit which makes everything taste bad. There are no such limits above 100°C. So slow boiling (at 100°C, as opposed to slow heating at much lower temperatures) doesn't change anything.

Point two: you can change cooking time by using quicker boil. Starch is unpleasant (raw) below 70°C, but it doesn't have an upper limit at which it gets unpleasant. (Technically, if heated enough, it first breaks down to smaller molecules and then chars, but you can't achieve this with boiling). So, if you use a pressure cooker, which boils food at above 100°C, you can get your starch cooked much sooner, and the taste will be the same as when boiled at 100°C (could have some changes in the aromatics due to easier extraction under pressure but also more breaking down at higher temps).

Point three: Steam won't give you higher temps than boiling water. Steam does pack more energy than liquid water per molecule: the heat energy as well as the vaporization energy. When it hits the under-100°C surface of the food, it condenses, giving up its vaporization energy. But the problem is that it is much, much less dense than water. Even with much more energy per molecule, you get less energy transferred to your food when steaming than when boiling. So steaming heats your food much slower than boiling, and it doesn't heat it to above 100°C unless you use a pressurized environment (and then the things I said above about pressure cooking with water come into play).

So, really, there is no reason to do it. If you want to know what interesting things can be done to food, read about the chefs who do modernist cooking, molecular gastronomy and the like. They are good at it, and have had years of head start to come up with good ideas. If they don't do it, it probably doesn't make sense.

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Hmmm, collagen starts melting lower than that (though it takes a really long time, but we're talking about low-temperature/sous vide for that to matter). More importantly, most of the changes you're talking about are texture changes. The really interesting flavor changes—caramelization and the Maillard reaction—take place at higher temperatures, generally anhydrously (doing it with water requires pressure). –  derobert Oct 11 '12 at 19:31
    
@derobert I checked it again. Turns out that type V collagen denatures at up to 68°C (becomes rubbery) but starts melting at 70°C. Maybe other collagens melt earlier, but this is the one important for beef stew. As for the difference of flavor vs. texture, you are right, I didn't go into in this answer and just used "taste" in a very general meaning, including texture changes; this is consistent with the meaning which interests most cooks who want to experiment. –  rumtscho Oct 11 '12 at 20:05
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The liquid water is max 100°C (right?), beyond that it should vaporize (right?)

Yes, but strictly no. Firstly the boiling point of water depends upon purity and pressure.

The purity factor is argued as a reason for putting salt into water - increasing its boiling point and hence cooking faster. In practice this has negligible effect (a brine strong enough for a wet cure would still only be about 102°C boiling point, so the effect on cooking time of a bit of salt is going to be overwhelmed by the pressure factor).

The pressure factor has two practical effects. One is that if you try camp-cooking high in the mountains, it's harder to cook anything or make a decent cuppa, because the boiling point is so low (okay, not that practical unless you climb very big mountains, but some people do). The other is that pressure cookers cook faster, because of the corresponding effect of using high pressure to raise the boiling point.

Secondly, liquids won't necessarily boil when they reach their boiling point. This has a practical cooking safety effect, in that if liquid is heated in a clean smooth container (hence no nucleation sites) in a microwave it's possible to get it to do this. Such super-heated water has enough latent heat to turn the water into vapour, but hasn't done so. Once you do something that gives it a nucleation site (blow on it, knock it, add something to it), it suddenly flashes into steam splashing steam upwards and boiling water outwards, with enough force to smash the container as well as the obvious scald hazard.

In practice though, barring the superheating case (won't happen in a pan) and half-way normal weather and altitude, then yes, 100°C.

Water vapor could be hotter than 100°C (but how much, in normal cooking conditions?)

Not in this case. It can in the cases mentioned above, but not in normal pan boiling.

As you add heat to water starting at, say, 20°C, that heat will cause the temperature of the water to rise. Each large calorie (kCal, the same sort unit used to measure the energy content of food) absorbed will raise a kilogram of water, 1°C.

Once the water reaches 100°C, yet more heat energy is needed to turn it into steam. This takes around 540kCals per kilogram - much more than the amount needed to raise the water by 1°C. Hence the water remains constant at 100°C for a while, then some of it turns into vapour. Now, it only takes .48kCal to raise vapour by 1°C, but that vapour is going to rise, moving it away from the heat-source and helping distribute the heat energy more evenly throughout the water (which after all, will be cooling elsewhere).

For this reason boiling water will be staying pretty much at an even 100°C (not precisely so, but precisely enough for cooking purposes.

Likewise, while ice can be much colder than 0°C, ice mixed with water will stay around 0°C as the heat absorbed goes into melting the ice rather than heating the water.

When boiling water, the vapor originates at the bottom of the pan

Some flashes near the top, but most does, yes.

So technically the foot could be "hit" by this vapor, thus being heated above 100°C

No for the reason given above. It's worth nothing that when the food is hit by vapour, that vapour contains more heat energy than the water at the same temperature, and while it can't raise the temperature any higher than 100°C, it can theoretically do so more quickly. However, liquid water is a better conductor than vapour water, which mitigates this. In all, this has no effect upon the cooking process, but it does explain both why a steam burn can be much worse than a liquid water burn - it's not normally the potential for vapour being above 100°C, so much as the greater heat energy to transfer - and also why one can put ones hand in domestic steam for longer than in heated water - the poorly conductive steam, mixed with air, is not as good at transferring heat, and hence causing injury, as liquid water is.

In all then, boiling water is 100°C, and this isn't a concern for cooking - if the recipe says to boil it, just boil it. The only real concern is to not let it boil dry.

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The big thing that can matter for cooking are that a more vigorous boil drives off water faster, is more rough, consumes more energy, and heats the kitchen more. Nice technical explanation of why all those other things don't matter for cooking. –  derobert Oct 12 '12 at 16:01
    
Thanks @derobert Worth noting that while the temperature won't matter, for the reasons I give above, the driving off water faster does have a cooking effect, since the ratio of food to water is increased. I mentioned boiling dry (and I have indeed managed to burn soup), but before that point it can also cause issues if you want a generous supply of water as in cooking pasta - drive off lots of water and you're left with a nasty high-starch goo. Not the concern the OP asked about, but still a way to ruin a meal. –  Jon Hanna Oct 15 '12 at 10:25
    
(And also, the microwave superheating is hard to do on purpose, but has caused injuries in normal domestic settings, and safety is always something to think about when cooking). –  Jon Hanna Oct 15 '12 at 10:26
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I sometimes use a pressure cooker, which cooks at over 100C and can have much quicker cooking times than conventional cooking. It is not known for adversely affecting the taste of food.

For some dishes it seems to improve the flavor, I'm not sure if this is due to higher temperature, less evaporation, or shorter cooking times.

So I wouldn't worry about boiling point at atmospheric pressure.

See pressure cooking on wikipedia

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I don't see how this answers the question that was asked. –  Marti Oct 12 '12 at 16:54
    
Hope edit had clarified this –  Jeremy French Oct 12 '12 at 19:59
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