This is a typical layout of a roast curve showing Bean temp, incoming air temp, and environmental temp. RoR (rate of rise), shown with the dark line, is a mathematical measurement of how quickly your bean temp is climbing.

The three major phases of dry phase, mid phase and development phase are derived by using charge, green-to-yellow, first crack and drop as our markers. At the end of the roast, the time in each phase is assigned a percentage of the overall roast time.

Bean Temp (BT): Lower right quadrant of drum front. Placed to be centered in the bean mass to make physical contact with the beans.

Drum Temp (DT): Located just left of drum axis on drum front. Measures the average, central drum temp and triggers alarms and auto-shut down if temps exceed safe levels.

Environmental Temp (ET): Upper right quadrant of drum front. Placed opposite the bean mass

Incoming Air Temp (IT): Located at the rear of the drum compartment. Measures air temperature after air passes by the burner set and before it enters the roaster drum.

Our first answer is always this: the thermocouple that came with your Mill City Roaster is the best size for that location. We use a mid-size diameter thermocouple that is responsive enough to create an accurate feedback loop but not so responsive that it your data is too noisy to be useful. Thinner thermocouples may respond to temperature changes more quickly but they also pick up outliers that should be dismissed.