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I don't have a kettle, so I use a cooking pot at home to boil water. I boil water on high in the cooking pot and as soon as I see the big bubbles/steam forming, I assume the water has reached 100° C. Is that correct?

If the water has reached 100° C and I let it settle off the stove for 1 min, what's the average temperature of the water after that period of time?

EDIT

I'm trying to make some coffee from my french press and from what I've read, people recommend to wait 1 min before pouring the hot water in the press. I'm not getting a lot of coffee flavour from the french press after letting it infuse for 5 min. I was curious to know if the temperature of the hot water can drop a lot in 1 min.

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    You are correct with the assumption that the water reaches 100°C when it starts to boil. As for the average temperature, I think it would be really hard to calculate since you would have to take into account what temperature the room is in and what not.
    – duchessofstokesay
    Commented Feb 12, 2011 at 14:25
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    Pick up the book Thermodynamics for Dummmies. It will help you calculate heat loss based on ambient room temperature and the size of the vessel.
    – Brian
    Commented Feb 12, 2011 at 16:59
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    I'm gonna be a bit pedantic and say, "Use a thermometer". It's really the only way to tell with 100% certainty (limited by the acccuracy of your thermometer, of course).
    – Marti
    Commented Feb 12, 2011 at 22:54
  • At the Engineering Toolbox: Heat Loss from Open Water Tanks: engineeringtoolbox.com/heat-loss-open-water-tanks-d_286.html
    – Wayfaring Stranger
    Commented Mar 21, 2016 at 20:02

6 Answers 6

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As long as you are talking about a normal pot with or without a normal lid (i.e. not a pressure cooker) and you are reasonably close to sea level, you're right, boiling water is at 100°C. However, if you start to climb in altitude, that is no longer the case, at 300m, water boils at 99°C, at 600m, 98°C and so on. Wikipedia has a page with information about High altitude cooking that contains a reference table.

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    ... and that it's mostly pure water -- if it's a solution (ie, there's salt or sugar disolved in it), the boiling point is slightly higher. (not much though, you can only raise it about °4C, and that's for a saturated solution, which would be very salty)
    – Joe
    Commented Feb 12, 2011 at 21:11
  • This would go for water in a kettle also though.
    – vwiggins
    Commented Feb 14, 2011 at 10:13
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    This doesn't answer the important part of the question, which is how fast the water will cool.
    – Cascabel ♦
    Commented Mar 21, 2016 at 20:04
  • @Jefromi No, but that was not the original formulation of the question (the one I answered back then).
    – PaulRein
    Commented Mar 31, 2016 at 9:04
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    @PaulRein It wasn't in the title, but it was the whole second paragraph of the body.
    – Cascabel ♦
    Commented Mar 31, 2016 at 14:20
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Tip: in your current phrasing, your question seems like a rather abstract physics question. You could get more informative answers if you expanded it to let us know what you are trying to prepare at a certain water temperature. Is it tea perhaps?

But to try to answer the first part of your question as stated: the Rouxbe cooking school has a video lesson demonstrating how you can identify different water temperatures without using a thermometer. For example, for the poaching cooking method (which is done in water at 71 to 85 degrees Celcius) you should look for the first small bubbles at the bottom of the pot and the first signs of steam from the surface. So assuming that the water is at 100 degrees Celsius as soon as you see steam forming is not necessarily correct. If you heat up the water further than the poaching temperature range, you get at the temperatures for simmering and gentle boiling. For a vigorous boil (100 degrees Celcius, which is the maximum temperature that water can reach at sea level) you have to wait until the water is moving and steaming faster, with big bubbles appearing on the surface.

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The cooling rate will also depend on the mass (volume) of the water, the mass of the pot, the thermal transfer capacity of the pot and anything it contacts, ambient temperature, air pressure, humidity, purity of the water, etc. The answer to your question is "close enough".

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I'd wait about 30 seconds. If that doesn't do the trick or tastes burnt, try more coffee. If neither of those work, you may have a lighter blend of coffee (can also happen if it's old). Also make sure to steep for about 4 minutes on average for a French press before pressing, you can play around with times to find one that suites you best of course, but 4 minutes is the average amount of time it takes water at approx. 195 degrees f to extract the intended amount of flavor from of the coffee that the manufacturers shoot for without making "too strong" or "too weak". All subjective though. Hope this helps a little! Saw everyone else trying to be Isaac Newton and not trying answer your question so I figured I'd at least offer what I know. Cheers!

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No one seemed that interested in answering the part of question about cooling time. Luckily, someone else has done a wee experiment and put it on their site:

http://jwilson.coe.uga.edu/EMT668/EMAT6680.2002.Fall/Ledford/ledford12/cooled%20_data.html

They also used a cooking pan.

According to their data and this excellent answer on Coffee SO which says:

Coffee solubles dissolve best at an optimal temperature of 195-205°F

the ideal moment to pour the coffee after boiling is around the 2nd minute, roughly between 90 and 150 seconds (though I've come to prefer cold brew, it tastes great and it's easy, which could be the real solution to your problem).

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  • Thanks for the data links. However, the reason why this question is unanswerable as written is because so much depends on the details. Your first link mentions that cooling rate depends on surface area (which is true), so the size of the pan/surface area is one variable. The volume of the water is another variable. The material of the pan/cup is another. Whether the cup/pan is preheated before adding the water is another. The temperature and humidity of the room are further variables. The only way to actually know the temperature in a particular setup is to measure the temperature.
    – Athanasius
    Commented Dec 26, 2019 at 14:17
  • @Athanasius Yes, specifics make a difference and the only way to know is to measure directly. That doesn't mean there isn't an average in either the specific mathematical sense or the more colloquial "what's it likely to be, roughly". It's not unanswerable any more than "how long does it take to get from work to home" is unanswerable. So, a data point is a good start.
    – ian
    Commented Dec 27, 2019 at 7:46
  • I agree, which is why I upvoted your answer. My comment was reacting to the first sentence of your answer, however, which implied that no one was interested in answering that question. I don't think it's that people were uninterested -- I think it's just impossible to answer with any specificity. IMO, the right answer if OP wants to find an "ideal moment to pour the coffee" is to get a thermometer and measure what happens for the particular equipment.
    – Athanasius
    Commented Dec 27, 2019 at 15:08
  • @Athanasius Fair enough. It's a tad rhetorical but I'm not above hyperbole :)
    – ian
    Commented Dec 27, 2019 at 16:03
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Boiling fresh water is indeed 100c or 212f at sea level. However your question is a very good one. If all the water in your pot were boiling, it would all vaporize very quickly.

The water just above the hot spots inside the tea pot are just under boiling, and reach boiling just as they vaporize, but the water convecting around the edges is much cooler.

In general, it is usually considered that if you bring tea water just to boiling point (the whistle just starts blowing), and you pour a cup of tea that water temperature overall is closer to 180F or 82C which is the perfect temperature for steeping tea leaves.

Coffee steeps faster in hot water as well. In fact you can make an appreciably better cup of coffee starting with hot water rather than cold water in a basic drip coffee maker. The hot water runs through the system faster which means less of the harsher elements of the coffee is extracted from the bean. Hot water equals swifter extraction which equates to better quality, where as just like with tea, If you steep too long, the tea loses its fresh quality and becomes astringent.

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