hot coffee

[Guest vikasj007]

i went with my friend and his wife to the coffee shop. the coffee was brought when my friend's wife was in the wash room. it was steaming hot while the milk was cold.we mixed the coffee and milk and started drinking. (considering the fact that i prefer my coffee without milk, take this case as an exception.)

 

now, i wanted to keep the coffee and milk mixed for his wife but my friend said it would be better to keep it separate till she came back as it would be hotter if it was mixed after she came than it were mixed right then.

 

who is right?

[Glider]

You are.

 

Rate of cooling is a function of the gradient between the coffee and the ambient temperature and a plot of cooling yields a half-life curve. Waiting to add the milk allows the coffee to cool relatively rapidly on its own, due to the difference between it and the ambient temperature. Adding the milk later will cause further cooling. Adding the milk early would cause the coffee to cool a little, suddenly, but subsequent cooling would be slower.

[YT2095]

HOWEVER!....

 

if you take into account the added surface area of the milk vessel reaching room temp, then as one cools the other warms!

[5614]

Adding the milk early would cause the coffee to cool a little, suddenly, but subsequent cooling would be slower.

 

yeah, the addition of the cooler milk would cause a short burst of accleration in the cooling down process, however, this same "burst" would appear at the same rate when you do it once his wife had come... the only difference would be that if you added the milk immediately it would have had more time for it to make its cooling effect by the time his wife had come, whereas if you added it when his wife came you'd have to wait a few mins for the same effect to happen.

 

also you must take into account that the milk would have nearered room temp and the cofee would have cooled down.

 

plus with the addition of milk theres be more volume for the heat energy to spread across.

 

im not sure, i dont think it would make much of a difference (except the bit underlined).

[YT2095]

it seems to me that coffee with or without milk, will cool at a very similar rate.

but with the addition of added surface area on the colder vessel (milk) there is a greater chance to absorb more energy, so she goes to the toilet with the milk temp at 10c and comes bach with the milk at maybe 12c there`s a gain, and that SHOULD offset the Loss at the coffee pot

[Lance]

Adding the milk first could involve removing the lid which would increase the rate of cooling even more.

 

What is it with people and hot coffee anyway? I add ice to my black coffee so it doesn’t burn my tongue. That way I can gulp it down too.

[kingjewel1]

In this case, i think it would be a matter of perception rather than science. The wife would think that it is hot as you tell her the reason you hadn't added the milk was so as not to let her coffee get cold.

Physically there is only the difference in time. Let it cool now, or let it cool later.

Thermodynamically speaking it is exactly the same. The milk warms so gains energy from the ambient. The coffee cools and so loses energy to its surroundings. Doesn't matter which way you do it. it's the same as the enthalpies are equal regardless of the route.

 

OneStone

[zpoot]

What is it with people and hot coffee anyway? I add ice to my black coffee so it doesn’t burn my tongue. That way I can gulp it down too.

 

i do that. Why doesn't someone try it out?? I don't really think it would make a difference though. Either way the coffee will be sitting there for the same amount of time and cooling down. To me, i think of it as the same process, just in reverse...

[Callipygous]

the other thing to keep in mind is the purpose of adding the milk. if the wife is adding the milk mainly for cooling purposes then depending on how long it takes her to come back, she may add less than you add initially. if you add milk and that sudden change plus the gradual puts it below where it needs to be then you messed up because she would have come back after the gradual and added just the right amount of sudden change to get the right temperature.

: )

[The Nacho]

Why don't you just buy some more coffee when she gets back? Then nobody would care.