I don't know if 400°F is hot enough, or not.
FWIW, my roaster blows hot air through a revolving roasting chamber. It has 2 thermocouples and a temperature display that alternates between them. One thermocouple, upstream from the roasting chamber, controls the heating element. And the other reads the air temperature as soon as it emerges from the roasting chamber with the beans. I routinely roast until I see 458 to 460°F on the read out. That isn't the temperature within a coffee bean while inside the roasting chamber, but it's the best I can do.
Once I get to that stopping temperature, I get the very hot beans out as soon as I can. I cool them in a mesh colander I put on top of a downdraft exhaust fan. The photo also shows another reason why I got that roaster. I can send the smoke outside with that downdraft fan and a dryer vent hose. Yes, roasting coffee is hot enough to make a fair amount of smoke.
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