Water Temperature Experiments for Coffee (1):

Water cools from boiling, we all know this – but just how quickly?

It’s a question that puzzled me, and I could find no quick answer on my google searches that met my needs – so what better than to go back into a science lab and do some real-life experiments!
Well, a kitchen. And a set of semi-controlled slightly made up conditions as I went along and made my observations. I’m sure a real scientist would be able to tear my kitchen table methods to shreds. But I thought doing these would at least point me in the right direction.

One of the first things I learned about coffee was “don’t pour boiling water onto the coffee” and as I have come to learn more I’ve repeatedly heard temperature being held up as one of the great variables affecting the coffee.

In geeky mode then, thermometer at the ready every time you make coffee and all is well I suppose?? But what if a coffee needs to be made quickly, or you just don’t have a thermometer to hand?? – is there a rule of thumb for how long you let the water rest after the kettle has boiled?

So my experiments began.

I might add that the first thing I found on the internet after I completed my experiments was a paper on how quickly water cools after boiling – but as I’d gone to the effort, I will document my findings here anyway!

I started by getting a jam thermometer (borrowed from my mother-in-law) as – fairly obvious I know – a regular one would not cope with the high temperatures I needed to record. And as with most things, although the idea of such an experiment had been rumbling around my brain for some time, the decision to actually progress with this had a fairly random timing. So rather than not do it, best get hold of what would be available.

The first set of observations I made was also using what else was easily available, a plastic jug. Probably not the material I would have chosen if I had actually thought properly about it!
I took observations every 15 or 30 seconds – in part depending what else was going on in the kitchen (but never leaving a gap of more than 30 seconds on these).

During the first time I decided that 10 minutes was about the right duration to keep going (a mix of what temperature had been reached and how long it would take to do all this: I realised early on that I would have to repeat the experiment so that I knew whether it was just a fluke).

My random nature in proceeding with these experiments meant that I hadn’t created a lovely observations table to record my readings – but was just scribbling the findings on some cut-offs of paper.

I also realised that the nature of the thermometer that I was using meant that depending on the angle of my head to the instrument I could come up with 1 of 3 readings whether my head was above, straight-on, or below the mercury (actually a coloured liquid: don’t know what they actually put in thermometers!). I think that’s most of my confessions out of the way on this exercise!

So a little haphazard, but off I ventured with this activity – trying to ensure I was learning quickly so as not to invalidate my experiments too much!!

At first I was a little puzzled that I couldn’t get a reading of 100 degrees Celsius from the water in the jug, no matter how quickly I poured and measured. I attributed this initially to the fact that the mercury (not really mercury, but we don’t know what it is) took time to get to the temperature – but later realised that the act of pouring the water would be cooling it down too. Another realisation (again obvious, but best to think about it at some point: was that the ambient temperature could affect the rate of cooling – I was doing my experiments in a room temperature environment (somewhere close to 20 degrees Celsius).

I did organise myself a little better as I went along. and transferred my readings to an excel spreadsheet before I had taken too many. So as not to get confused, to have a proper saved record, and to be able to perform some calculations on them and chart them.

So by the end of the experiments some sense of order had been enforced.

Headlines were: that the water was at c 95 degrees Celcius within the first 15 seconds, that it had dropped to under 90 degrees by around a minute, and 85 degrees by between 2 minutes 15 to 2minutes 30. And that the rate of cooling was quickest at first, and then slowed.

The average of 4 observations is charted in the attached diagram (observed temperature – in degrees Celsius – on the vertical, and time since boiling – in mins:secs – on the horizontal).

I repeated the observations about 3 times- and was surprised at how consistent my results were (to say it wasn’t exactly lab conditions, that my eye level could have thrown it, and that the starting temperature of the vessel would have been different between the first time and subsequent times – when it would have been warmer)

Thinking about what might have affected things did lead me to conduct some slightly modified versions to explore different situations too. But I was pleased with my initial findings – charted below.

Temperature vs Time
The Time Taken for boiling water poured into a jug to cool.

More to come……

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)

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