As a heat averse person who grew up unhappily in sunny Southern California and still mostly has to unstoically endure warmer than you'd think Minnesota summers, one might guess that I am wary of hot beverages. I am. I am very wary. When I go to a mystery cafe somewhere and order their $4 cappuccino I am disappointed if the espresso is poor and badly pulled, or the milk is evil and hormone laden, or the drink's presentation is bad, perhaps slopped in some narrow paper cup, but the one thing that really breaks my coffee loving heart is when the drink is too hot. I don't care how hot regular old coffee is so long as it is absolutely safe to drink without any danger of burning, and I believe that a cappuccino is properly served just barely over the hot side from very warm.
For cappuccino I have a technical, scientific justification for my preference. The glorious microfoam made in steaming milk, that light, liquid, magical stage of creamy frothed milk, is produced strictly in the warm to very warm stage of steaming. As the temperature progresses into "hot", your beautiful, delicious, velvety, exquisite, and perfect microfoam will evolve into that dreadful, stiff, and flavorless foam that is dramatic, pointlessly divorced from the espresso, and difficult to consume. You have had this in many of the bad coffee shops you have ever been to. And there is a very reasonable chance, with the overheated milk and hard foam covering it like a layer of roofing insulation, that you burnt your tongue on it.
I always burn my tongue on it. I hate burning my tongue on it.
Do I have all the research and technical data to back up all the science in this post about hot coffee?
No, no, I just make stuff up here, and I hope that the plausibility of it all will wander over to the land of truth, and there take up residence.