stupid question about the temp. of my coffee

When I go to get my cup O coffee in the morning, will it be warmer if:

  1. I fill the cup 1/2 way then add the cream and sugar, then top it off, or

  2. I fill the cup the whole way and then add the cream and sugar and stir.

Or does it not matter because there is still the same ratio of coffee to cream no matter what?

Pretty stupid huh? :rolleyes:

The rate of heat loss is proportional to the temperature difference between the coffee and the air. That is, the hotter the coffee, the faster it loses its heat. Which means you should put the cream first then pour the coffee on top.

That way of doing it is almost guaranteed to cause a spill, I can tell you that much.

You’re one of them “hot water freezes faster” people aren’t you?
Although true that heat transfer is proportional to the [symbol]D[/symbol]T, there’s much more involved. The majority of heat lost from a cup of coffee is a result of conduction through the coffee cup and then a combination of convection and radiation from the cup to the air. Radiation plays a big role in this because (if I remember my Heat Transfe class right) convection is proportional to [symbol]D[/symbol]T[sup]2[/sup] whereas radiation is proportional to [symbol]D[/symbol]T[sup]4[/sup]. I’m sure Anthracite will be here soon enough to correct my shoddy recollection. We did an analysis once in college to look at the cooling rate of coffee in two identical cups, one aluminum and one white ceramic. The ceramic one cooled off faster because of the radiational characterisitcs of the material.

If this layman is interpreting Why A Duck right, you need to preheat the cup or use an insulated cup. This seems similar to the idea of getting a beer in a frozen mug.

And my thanks to KneadToKnow who made an excellent observation, even though I don’t use cream or sugar.

Preheating is the way to go. On weekends at home, while my private pot of Columbian is brewing, I’ll put hot tap water in the cup and let it sit. A preheated cup keeps coffee warmer longer.

The best way: heat the cream and the cup. I add cream or milk to my cup before adding coffee, and put it in the microwave for 20-30 seconds. This heats the mug and the cream up. Then add coffee. It stays hot forever.

Also, the coffee make you use makes a difference. Despite the fact that they’re expensive ($80-$150) and tend to break frequently, I continue to buy Capresso coffee makers because they heat the water to it’s proper temperature before making coffee. The result is a much richer cup of coffee without any bitterness. The coffee is hotter when you pour it, and stays hotter for longer. Capresso is the only manufacturor that I’ve found that does this properly.

I know I was over-simplifying. But are you disputing my conclusion? (i.e. with given cup, cream and coffee, putting cream first will keep the coffee warmer.) Or just the reasoning behind it?

By the way, radiational cooling is proportional to T[sup]4[/sup] not [symbol]D[/symbol]T[sup]4[/sup].

I was caught up in the excitement of using the symbol font. :wink:

Let’s see if I understand your proposition. We can have two situations:

A) Add hot coffee to cool cream. Theoretically this will temper the temperature of the coffee and thus the heat transfer rate will be lower.

B) Add cream to the hot coffee. Doing this allows the hotter coffee to sit in the cup for longer, thus giving off heat at a higher rate while you smell the cream to make sure it’s still good.

My only problem is that even if the coffee is giving off heat at a higher rate, eventually the temperature of the coffee with cream added will equal that of the cream with coffee added. From that point out the two heat loss rates should be the same.

Am I missing something?

I re-read the OP and you’re right, the difference would probably be neglible. There will only be a difference if you let the coffee sit for a while before adding the cream.


That’s my motto, kniz: If you can’t be insightful, at least be observant.

I’ve seen this discussion before. I don’t remember the resolution (if any). But I do remember one point. The amount of heat given off depends upon the relative surface area. If you add cream, the relative surface area decreases.

I avoid the whole problem by not adding cream or sugar to my coffee.

I for one like my coffee like I like my women.

Pale and sweet.