I'm going to answer the question that has plagued humankind for millennia.
If you're making a cup of tea
Should you put the milk in straightaway?
Or should you wait and add the milk at the absolute very last second?
Now some people will try and convince you that
of course you have to put the milk in first because the tea tastes better that way.
Well actually when people drink tea in a blind taste test the best way to
enjoy tea, they can't tell the difference and so actually putting the milk in
first was just a way to protect delicate cups. Whereas now in our modern
age of sturdy cup-wear you can go as hot as you want as fast as you fancy.
Rock the casbah. So putting in the milk isn't a matter of taste or safety,
it's merely a matter of which will keep your beverage the hottest the longest.
Now some people will wait, they will put the milk in at the absolute last second
because they think that's going to keep it hotter.
but that's not the case.
If you look at the Stefan Boltzmann equation for the rate at which a hot
body radiates heat, it's based on the fourth power of its absolute temperature.
So the temperature in Kelvin minus the fourth power of the ambient temperature, again in Kelvin.
What that means is hotter objects radiate more heat.
Hot objects cool down faster, and because it's a fourth power it makes a substantial difference.
Something at 80 degrees Celsius compared to something at 100 degrees Celsius
The hotter 100-degree beverage will lose heat 1.5 times as fast.
To put all of that into a plot obviously when you add
the milk early on it does lower the temperature of your beverage, but then if
you compare it to a beverage without milk it will lose heat at a slightly slower rate.
I mean it's a bit difficult to tell but there is a difference. What that means is later on when you do
add the milk to the other beverage it drops below the original one.
So it's definitely worth putting the milk in first and stemming the flow of that heat.
That's the idea in theory at least. Now I do get very excited because it's a fourth power.
I love spotting fourth powers in the real world.
If you have anymore examples please do let me know. But I wonder does it actually work, and I even
mentioned this in a recent BBC radio 4 series. At festival of the spoken nerd we did
a show for radio for called domestic science and I go on about fourth powers,
cups of tea, and all this. But I always thought you know what?
I have never actually checked.
And so I have gone and bought a digital thermometer which I can power up ... there.
And it's got two different probes. Let me get the right one.
This one here is T1, it's actually labeled as T, so I'm gonna call this one here T1.
I can put that probe in there. And this one here is T2, so I can put T2 in the
That's not right, i'm going to have to
Alright so now that is T1 not going anywhere from that cap, over here we have
T2 not going anywhere from that cup. Now the moment they should be
registering about the same temperature. So actually I can put this screen up so
you can see it. And if you go through the different options what we have at the
moment is T1 we can switch to T2, see both the same temperature.
pretty much the same. Over here we've got T1 minus T2 which is currently 0. So if I
actually heat up T1, if i put my finger on it. It's moving up, you can see the number goes up.
Now it's much hotter than the other one, and any second that should
cool back down again and we will be good to go. Just top that back up so it's
definitely boiling. Now my theory is if we add the milk straight away to T1 it
will cool down so you'll see the number go negative, but then later on if we wait
five minutes, and I add the milk too
T2 it will drop below T1 and so we should then get a positive value. And that
final positive number will be the number of extra degrees of warmth that we kept in
T1 by putting the milk in straightaway. So I've genuinely never tried this before,
it may not work, obviously reality is much more complicated than theory.
We'll give it a go okay so our initial temperature difference is pretty much
0 i'm going to put the hot water into both and we'll let the tea brew initially.
There we go.
Cup of tea.
Now let's just check the temperatures we've got going on. So if we go over here
T1 is 82, 81, it's cooling down a little bit, I guess the thermometer's
in a sense getting used to it.
Likewise T2 is about the same. So they're both about 81 degrees.
Wow that is substantially......
Is one at the top and one, no they're both at the bottom.
That's already quite a big difference. Why is there already a difference!?
What if I stir them, I'll stir them.
Give it a stir.
Take out the teabag.
Give that a stir.
Take out the teabag.
Okay how we doin' now? So...
Okay they are within a degree of each other.
You had me worried. So 78, and they're both 78.
Ok so now they're the same temperature I'm going to add the milk to T1, and then
we'll give it five minutes. Here we go and the milk is
We have started the timer. I might actually give that a stir just for completeness.
In theory the temperature in T1 that's 10 seconds so far
That's -5 degrees.
Initially by putting in the milk,
30 milliliters of milk.
I've dropped the temperature of this one by about five degrees, and we'll just
give it 5 minutes that's 30 seconds so far and
then we'll come back and see how we're doing.
Oh, I'm not going to make you sit through the remaining 4 minutes and 20
seconds of waiting for the tea to adjust temperatures. I will skip through some of
the highlights as such if you want to watch the entire cooling process,
as always I will upload all the footage unedited on to my second channel there's
a link in the description. You can check it out in case you want all of this delicious data.
A minute thirty.
2 and a half minutes.
3 and a half minutes.
4 and a half minutes.
We are done.
I'm dumping in the other lot of milk into T2 I'm going to give that a quick
stir for completeness. And I'm going to check out please be a negative number
And it is...
What is, wha, i, hang on...
No that's right, I want a positive note i want a positive number because
this one's hotter than that one. I forgot which way around I put it.
So around 2.25, 2 and a quarter degrees.
T1 is 2.25 degrees warmer than T2, because I put the milk in first.
It lost heat slower. It radiated less heat compared to the other tea and it
actually ended up warmer that's so good. That's actual maths in practice and in reality...
Oh, that's pretty warm, that's good actually.
This one over here.
Oh that's much colder. Oh that's ew that's tepid
I genuinely can't tell the difference, hang on.
I've totally convinced myself that this one is hotter.
Ok let's check it out in absolute terms.
We switch over to T1
So that did raise, and the other one is 61!
So there you go, T1 is 61.4, and T2 is 58.
Look at that!
So I mean either I've convinced myself, I'm very open to suggestions or you
genuinely can taste the difference over just five minutes change.
So there you are!
I took some maths I took some physics, that I've for ages told people about my
theory and finally I've checked and it does work.
in the fourth power.
I should have said may the 4th power be with you.
I'm an idiot.
One last thing.
The only way to be guaranteed scoldingly hot tea is if you drink it out of a
mug like this which I have carefully altered so that it is powered and it
keeps the tea constantly boiling while you drink it. You might think that sounds
unsafe but frankly i'm prepared to put my body on the line for correct proper
British tea. It is sadly mains powered which can get a little inconvenient i'll
I'll just pop this down here.
Bring that up...
Okay that is
substantially more on fire than I expected.
How strong must tea be if it burns!?