Coffee Roasting Datalogging & Automation

for beginners

What is datalogging?

Datalogging in coffee roasting is the tracking of temperatures at different locations inside and adjacent to the roasting drum before and throughout the roast. These temperatures are measured using metal probes called thermocouples and the results are typically tracked on a line graph commonly referred to as a roast curve or roast profile. Essentially, you are tracking the environment you've created inside the drum with your fuel and fan settings and the reaction the coffee seed is having to that environment by tracking the temperature of the bean mass.

The primary use of a roast curve is as a recipe which can later be referenced to verify batch consistency as part of your QC process or to diagnose a machine or venting issue. For experienced roasters, this data can become a biographical roast craft reference and allow for season-to-season referencing of origins, varietals, processing methods and roasting equipment to better predict how a new green should be roasted.

All that being said, you cannot taste a roast curve. Roast curve data will be an invaluable tool in your roasting career but the success (or failure) lies in the cup. Roast curves should always be weighed against tasting & cupping notes.

Frequently asked datalogging questions

Typical temperature tracking

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.

Thermocouple Placement

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.

Available data by model

Below is the data offered by each of our Mill City Roasters models via the USB connection on the control panel. Also noted is which models are Roast Replay™ and automation capable when using RoastPATH® as your datalogging software.

Air Temp


Operator Assist
Roast Replay™ and
automation capable
with RoastPATH®?



Learn more

RoastPATH®: Roast precision redefined

Readable data by platform

We built RoastPATH® specifically to manage the extra data and capability our coffee roasters were design to offer the modern coffee professional and other platforms are still able to read the data they typically display as well.

  Artisan Cropster® RoastPATH®
Record BT
Record DT
Record ET
Record IT
Record fuel adjustments
Record fan adjustments
Record drum speed adjustments
Auto-record charge time & temp
Auto-record turning point time & temp
Auto-record drop time & temp
Roast Replay™ automation

Have questions?

CALL (612) 886-2089