# Which cools hot coffee quicker: milk into coffee, or vice versa?

I’ve always wondered, if you pour an inch of milk into the cup, and then the coffee, does that make the eventual mix cooler than if you pour the coffee first and then pour the milk?

All other things being equal, there end concoction will be a smidge cooler if you pour the coffee through the air- the air acting to cool the coffee.

Assuming you don’t actually ‘pour’, but very carefully and slowly add the second liquid (using some kind of device so the second liquid is barely moving as it touches the second) so things don’t get mixed?
I’d guess milk first would be a tiny bit cooler, as the hot coffee will be on top exposed to the air and therefore cool more by evaporation and convection.
If the cool milk is denser than the coffee, then things will be sort-of stable in that position and the coffee might even cool noticeably, but I’d expect whole milk or cream to be less dense than coffee (the fat is less dense than water), so things will get mixed fairly quickly.

Again, if you’re just pouring from a pot into a cup, I think things are going to get pretty well mixed just from the pouring, regardless of which one is poured first.

The real answer is to pour the coffee first, let it cool as long as possible, then add the cool milk.

As a first approximation, it makes no difference. The final temperature of the eventual mix of coffee and milk just depends on the beginning temperature and heat capacity of each. It doesn’t matter if you and milk frst, or coffee first, or do them at the same time, or alternate, the final, “average” temperature will be the same.

I’ll wager that that “first approximation” solution is pretty accurate, in that you’d be hard-pressed to measure any difference with a typical thermometer. However, there will be some small differences between putting the cooler liquid in first and putting the hotter liquid in first due to the heat transfer from the unmixed liquids. The end result of these effects will depend, I think, on how long each unmixed liquid is allowed to sit. However, I suspect the effects are small.

There’s another factor to consider. If you pour the coffee in first, and then add the milk, that first bit of milk that goes in will come up to coffee temperature quite quickly. I don’t know if that’s enough to make it curdle or spoil, but if you pour the milk in first it would have a greater heat-sink effect and would stay cooler during the mixing process.

Adding a spoon will cool it off faster as it will act as a heat sink.

Apparently the “coffee/cream” question has been kicking around for years. These two URLs are "simple"ones

The most physicist-ty, and mathematics-y, and completely un-understandablyto me, is

These are for cooling dynamics over time, as far as I can see. Can someone restate what’s going on in these papers, and how/if it differs from my problem?

If someone above did already did explain when giving me a comment and it went right over my head :smack:, I’m sorry. I enjoy talking about physics if it’s nice and slow…

wg rees On cooling tea and coffee - Google Search is the correct link to the hard-core coffee/cream pdf.

Not an exact answer to your question, but perhaps the answer to a similar but different question will help:

http://rec-puzzles.org/index.php/Milk%20and%20Coffee%20Solution

The coffee cools by heat diffusion. The rate of diffusion is higher when the temperature gradient is higher, which means that a hotter liquid (i.e. coffee without milk) loses heat faster than a cooler liquid (i.e. milky coffee).

Therefore, pouring the coffee first cools it faster than pouring the milk first. Simples.

(For simplicity, I’m assuming the cooling effect of the milk is the same whether it’s poured first or last, but of course leaving the milk in the cup at room temperature for any length of time would warm it slightly, and it would then cool the coffee less).

Your first link answers a different question than the one you asked: it examines when to add cream to coffee (early or late) rather than which to pour into the cup first.

The second link essentially says that coffee first or cream first should make no difference, save for the small effect of the heat stored in the material of the cup itself.

Your third link, even after correction, is to a Google search and not a pdf, so I can’t comment on it.

Guys, thanks. I’ll have to think/read about these pieceas when I’m not so burnt out. It’s on my mind a lot though, and I’ve already bugged two waitress friends if they’ve ever thought about it. You can guess their general responses.

BTW, the PDF for the hard-core (to me) physics paper shows up as the first hit on Google Scholar search under Rees, On Cooling tea and coffee. It’s also somewhere in regular Google…

Thanks to all.

[PDF] ►On cooling tea and coffee

WG Rees, C Viney - American Journal of Physics, 1988 - loreto.unican.es

Seven years have gone by since this refreshing thread, and the zombie now wakes up–grumpy and demanding his reviving cup, here supplied. It is a recipe for something we all know, but was at the time somewhat exotic fare (I’m guessing the 1970’s, but couldn’t find the source). It needed an intro, which I found interesting in this context. The (translated) text is by the recipe author, Vincenzo Buonassisi, in his Il Caffe.

Not having been able to read this thread, Vincenzo reasons incorrectly, of course. The hairline effect–if it is to be believed (I haven’t tried it)–must be from the sugar density in the milk. Grab them by the pousse-café, I always say.

Cappuccino
There is a way of enjoying coffee that I learned when travelling near Sorrento. I asked for cold milk in my cappuccino to refresh me from the heat of the south, and the barman poured the milk first and then the coffee. Because of the differing temperatures, the two liquids did not mix and the coffee remained on top. I did not add sugar and did not stir, so the two liquids remained separate. When I sipped my cappuccino the milk and the coffee reached my palate separately; one hot and one cold, one slightly sweet, the other bitter.

To make 3[sup]1/2[/sup] cups/875 ml:

1[sup]3/4[/sup] cups/425 ml cold milk
1[sup]3/4[/sup] cups/425 ml very hot strong coffee
sugar (optional)
cocoa powder, ground cinnamon or grated nutmeg (optional)

Pour out the milk into individual cups and add the hot coffee. Add sugar to taste, if you like. Do not stir. Cocoa powder, ground cinnamon or grated nutmeg may be sprinkled on top.

The recipe is cited in the volume Beverages from the redoubtable out-of-print Time-Life series The Good Cook, edited by Richard Olney.

I can’t speak to the revival of the thread, but as to its first decade I argue the practical best is cream (*never *milk :eek:) first then coffee. So of course that’s what I do.

Do it that way and by the time you’re done pouring the coffee the two fluids are well-mixed and ready to drink. So no need to stir or to waste time stirring. Both those extra factors would cool the mixture. Especially so if one stirs with a proper metal spoon vice a Philistine plastic or wooden stir-rod. So avoiding those extra steps keeps the mixture warmer. As it should be.

I have read somewhere, a lengthy discussion about what to do if the coffee is going to stand for a while before being consumed; as in the case of I buy a cup for my friend who has yet to arrive.

Do I add the milk/cream on the ground that this will lower the temperature of the mixture and therefore reduce the rate of cooling. Does putting the saucer on top achieve anything? Should I drink hers too and let her buy her own when she finally turns up? Well, one has to think about something while one waits.

No. The rate of cooling will naturally fall as the coffee drops in temperature. It doesn’t need help.

Yes. Of course. This assumes you aren’t at Starbucks and have a plastic lid. In such case, forget the saucer.

Not if you have ulterior motives.

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Sure, but if the cream is going to be added in anyway, adding the cream in first is going to keep the final temperature higher than adding it in at the end.

Assuming the milk/cream starts at refrigerator temperature, waiting to add it should help because room temperature air is warmer. The milk is actually picking up some heat from the air as long as you keep it separate from the coffee.

But starting coffee temp (say 175F at Starbucks) is around 100 degrees higher than room temp (Assume 70F). Even if the cream started in the refrigerator at 32F, there’s only a 38 degree delta there. There’s much greater opportunity for the hot coffee to cool off than the cold cream to warm up, since heat transfer is directly dependent on the temperature delta.

You’d have to assume a room temperature of more than 107F before you’d want to keep the cream separate until the end, assuming all else is equal.

Mr. Twinkie is right: If your goal is to have the coffee as hot as possible at the end of the waiting period, then unless you’re outside in the Sahara at midday or similar, or the cream is nitrogen frozen, then mix them before waiting. With more or less normal room temperature, refrigerator cream, serving temperature hot coffee, and no particular insulation for the coffee, unmixed coffee will lose more heat than the cream gains.

BTW, putting a saucer (or any other lid) over the coffee will also help, probably by orders of magnitude more than mixing the cream first.