From my initial inquisitiveness about what temperature is reached when you leave boiled water standing, a whole lot of other questions gathered. The reason for the initial inquisitiveness was about making good coffee and having some idea of what temperature the water might be at when there is no thermometer to hand: because the taste and characteristics of the coffee are affected by the temperature of the water.
From in initial set of observations and thoughts, I had a need to try some different scenarios to explore whether all the things that I thought might affect the rate of cooling had any meaningful effect.
Actually on my first modifications, I didn’t really get any very different results from pouring the water into a ceramic mug to cool rather than the plastic jug. I guess if my observations were more precise there might have been a small discernible difference, but obviously not big enough to show up for me.
However, measuring the temperature of the water in the vessel where it was boiled (electric kettle in my kitchen experiments) made a big difference – seemingly in the rate of cooling and in the temperatures reached in my 10 minutes of recording temperatures each time.
Not really surprising, but I’m attributing this (perhaps rather rashly, but it seems logical) to the cooling on the water from the pour from the kettle to the jug (or mug), as well as to the fact that the tapered shape of the (at least my) kettle exposes less water directly to the air.
Lilac line represents observed temperatures of water in kettle at time (mins:secs) since water boiled.
Rather than getting to c 95 degrees Celcius within the first 15 seconds, that temperature wasn’t reached until 2 and a half minutes. And the 90 degrees wasn’t breached until after 5 minutes of cooling, rather than approximately 60 seconds in the open-top experiments as I’ll now call the first set!
It took over three times as long for the water to cool to c85 degrees Celcius: 7 and a half minutes rather than approx 2minutes 30 in the open-top ones. The rate of cooling also seemed fairly steady in these Kettle experiments rather than changing (slowing down) in the open-top experiments.
Lilac line represents observed temperatures of water in kettle, yellow line for water in open-top container.
This means that if using a rule of thumb as to what temperature the water is at some time after boiling, there could be some great differences depending on where your water is (in relation to where it boiled).
More to come – as we still haven’t got to an answer that is practical ……
please note: boiling and hot water can be dangerous if not handled with care!
(despite the haphazardness of some of my approaches above, I did take some care and would suggest anyone else does the same: and children should be accompanied by an adult)