At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the influence of viscosity on the evaporation rate.
My question is twofold:
- Is his conclusion correct?
- Are those reasons relevant?
The question is somewhat open-ended, because "20% slower" could refer to the instantaneous cooling rate at $t=0$ or to the time needed to reach some lower temperature. It would be great to consider both parameters in the answer (will they behave the same?)