What is the turning point in coffee roasting?

The turning point is the lowest point on your bean temperature curve - the moment the temperature stops falling and starts rising again. It happens shortly after you load the green coffee into the hot drum: the cold beans temporarily pull the temperature reading down before the thermal balance reverses and they begin absorbing heat from the drum.

In one sense it's just a reference point - you can't do much about it in the moment. But where it lands tells you something useful about how the roast is set up. A very low or delayed turning point suggests the charge temperature wasn't high enough, or the batch is large relative to the machine's capacity. A turning point that arrives unusually quickly might indicate the drum was running hotter than intended.

Logging the turning point consistently is part of building reproducible profiles. If it varies significantly between roasts using the same parameters, something else in the setup is drifting - ambient temperature, batch weight, or machine warm-up time are the most common culprits.