I've noticed in my convection oven, there is a difference between the air and the surface temperature of the metal baking pan on the top shelf.
Which is the better reference for measuring oven temperature?
And, does the answer change depending on what is being baked and the method of baking?
Notes:
In this specific case I'm baking baguettes on said metal baking pan.
I use an IR gun for the surface temp of the pan and an oven thermometer hanging from the same top shelf for the air temp.
If I place the oven thermometer on the pan then both show the same temperature.
Best Answer
Generally speaking ovens are controlled by a thermostat that (to a first approximation) measures the air temperature. This is what recipes expect. It's also why for some very sensitive baking it's not sufficient to preheat until the thermostat says the setpoint is reached, as the metal inside (e.g. shelves) hasn't yet warmed up (and a reason for sometimes preheating a dish or using a pizza stone). A lot of heat in the air is lost when you open the door, heat in solid contents much less so. Note that not all the air is at the same temperature anyway.
I would expect the temperatures of the air and a pan to converge over time, if you can avoid opening the door: the element heats up the air, the air heats up the pan. There may also be radiative heating of the pan from elements either visible or embedded in the walls/floor of the oven. For element you can also read "flame" in a gas oven.
If heat is mainly transferred through the air, the air temperature will rise faster than that of the pan (possibly much faster), but once the air temperature reaches the setpoint the pan temperature will catch up.
If radiative heating of the pan is significant, it could heat up ahead of the air and therefore exceed the setpoint, but once the setpoint is reached and the element switches off, it will cool to the air temperature.
If you keep opening the door to measure using the IR thermometer, all bets are off, so to track convergence you'd be best using two oven thermometers, one in the pan and one suspended from a rack. Make sure you can read both without opening the door, and make sure they read the same.
Although it's the air temperature that matters, if coooking something sensitive you should preheat until the metal and air are close to the same temperature, and then the air temperature will recover quickly after you (quickly) put the bread in.