I made myself some spicy chicken and macaroni soup, and put it in a bowl as it was boiling. It I put a thermometer in at as it cooled and I could eat it. I figured the soup was a good thing to test as I could take big bites that included liquid and solids that required chewing.

I took a bite every minute or so and noted the temperature, and I repeated with boiling soup after it had reached "too cool to enjoy".

At temperatures over 190F (87.8) I couldn't put it in my mouth without giving it time to cool on the spoon and "blowing on it".

At 180F (82.2C) I was still "blowing on it", but not in an unpleasant way for the first bites of soup. I would consider that to be optimum serving temperature for soup.

At 170F (76.7) I could it straight into my mouth without pausing or "blowing on it" but it was still a bit hot, if I were eating without paying attention to the temperature, I *would* have "blown on it"

At 160F (71.1C) I can and did eat comfortably. It was just pleasantly hot.

At 150F (65.5) it was still pleasantly hot.

At 145F (62.7) It was still quite warm, pleasant for soup.

At 140F (60C) it was still fine, but not hot at all.

At 135F (57.2C) it was still OK, but definitely getting on the cool side for soup.

At 130F (54.4C) I was glad to be almost done.

At 125F (51.7C) I was thinking seriously about the microwave.

At 120F (48.9) It was too cool to enjoy this particular soup.

Obviously, different foods are going to have different optimal temperatures. I wouldn't want steak to have ever hit over 130F (45.4C).

Also, consider that I have been cooking for 35 years. I am accustomed to sticking a spoon into something boiling on the stove in order to taste it.