What is the cooling stage in coffee roasting?

The moment you drop the roasted beans from the drum, the roast isn't quite over - residual heat inside the bean keeps development going. The cooling stage is the process of removing that heat as fast as possible to stop development at exactly the end point you intended.

Beans discharge onto a cooling tray with a rotating arm and a fan drawing cool air through from below. The goal is to bring bean temperature down to ambient in around four to five minutes. Too slow - from an undersized tray, a weak fan, or an oversized batch - and the beans coast past your intended profile. A roast carefully taken to 210°C can effectively finish at 212°C or 213°C if cooling is sluggish, shifting the cup in ways that aren't always obvious until the next day.

If you've ever had a profile that looks right on the logging software but tastes consistently darker than expected, cooling rate is worth checking before you adjust anything else.