The (Beautiful) Physics of Adding Cream to Your Coffee
Here’s a quick scenario for you. You’ve poured yourself a fresh cup
of black coffee, and you want to keep it hot until you’re ready to drink
it. Are you making a mistake by adding cream to that coffee? Does
coffee with cream cool faster than black coffee left alone? Intuition
says yes. The laws of physics lead to a different conclusion.
Last year, the web site Modernist Cuisine gave three reasons why “coffee with cream cools about 20% slower than black coffee” alone. To summarize:
1) Black coffee is darker, and dark colors emit heat faster than
light colors. As such, “by lightening the color of your coffee, you slow
the rate at which it cools,” if only slightly.
2) The Stefan-Boltzmann Law (apparently)
says that hotter surfaces radiate heat faster— than cooler ones. So if
you add cream to a cup of black coffee, it might lower the temperature
of that cup of coffee. However that cup could still cool at a slower
rate than a cup of hot black coffee.
3) Finally, and perhaps most importantly, “adding cream thickens the
coffee (adds viscosity), so it evaporates slower.” And, in turn, less
heat gets carried away by the evaporation.
To top things off, Modernist Cuisine also
produced a video showing cream being poured into coffee in super slow
motion. Even if you don’t care to consider the physics of coffee &
cream, it’s pretty cool to watch an average cup of joe getting turned
into a roiling sea.
via Petapixel
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