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I hope this is the appropriate forum for my question. I also considered posting it in the chemistry forum.

When I eat ice cream I often stir it into a texture similar to that of soft serve. During the process, the bowl in which the ice cream is kept, tends to become quite cold. Temperature measurements indicate that the temperature of the ice cream increases in the stirring process, so it seems to be the case that the bowl gets cold as a result of heating the ice cream.

I am however not quite sure about why the ice cream is heated. Could it simply be that stirring the ice cream constantly brings parts of lower temperature to the surface thus speeding up the heat transfer that would otherwise occur anyway?

Thanks in advance!

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This is a bit of a soft question (get it?).

Intuitively, the ice cream and bowl (and your hand) will move towards a state of equal temperature (second law of thermodynamics). When you stir the ice cream you are doing at least four things:

  1. you are 'encouraging' the heat to become more uniformly distributed (as you suspected),

  2. causing the ice cream to come into contact with regions of the bowl from which it has yet to absorb energy,

  3. causing the ice cream to adopt the same shape as the bowl and thus increase its contact area (and therefore the rate of heat exchange), and

  4. adding (a tiny amount of) energy by stirring it.

This has a rather noticeable effect on the texture because ice cream contains ice crystals and air bubbles.

Edit: Today I stumbled upon a book on The Science of Ice Cream, for those interested.

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  • $\begingroup$ Thank you for your reply! I upvoted for usefulness, but I will wait a little before I accept it. $\endgroup$ – Étienne Bézout Sep 13 '14 at 20:32
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    $\begingroup$ @ÉtienneBézout Please do - there are probably other effects I've missed. P.S. I stir my ice cream too. $\endgroup$ – lemon Sep 13 '14 at 20:33
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    $\begingroup$ It's much tastier that way :) This is maybe a bit OT, but it seems to me that the stirring does something more than just raise the temperature. When ice cream slowly melts, it doesn't seem to get the texture that stirred ice cream has. $\endgroup$ – Étienne Bézout Sep 13 '14 at 20:38
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    $\begingroup$ @ÉtienneBézout Ice cream contains ice crystals and air bubbles so warming it up very slightly does have a significant effect on its composition. $\endgroup$ – lemon Sep 13 '14 at 20:46
  • $\begingroup$ I agree with the other points, but I question "3. adding energy by stirring it" – in this case, this is surely negligible, no? What are we talking about here, somewhere around a Joule? That would heat the ice cream by a magnitude of 1 millidegree. $\endgroup$ – Zano Sep 14 '14 at 11:56

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