Roast Profiling and Curves

What Is Roast Profiling?

Roast profiling is the practice of recording and controlling the temperature trajectory of a coffee roast over time. By instrumenting a roaster with thermocouples (temperature probes) and logging data with software, roasters can visualize what happens inside the drum, identify cause-and-effect relationships between heat application and flavor, and reproduce successful roasts batch after batch.

The Core Measurements

1. Bean Temperature (BT)

A thermocouple inserted into the bean mass measures the temperature of the beans themselves. This is the most important measurement. The BT curve shows:

• Turning point — the lowest temperature after green beans are dropped into the hot drum (typically 80–110°C). This is where endothermic drying begins.
• Maillard onset — approximately 150°C, where browning reactions begin
• First crack — approximately 196–205°C, the audible structural fracture
• Drop point — the BT at which the roaster ejects the beans

2. Rate of Rise (RoR)

The rate of rise is the first derivative of the BT curve — how many degrees the bean temperature increases per minute. It is displayed as a secondary line on the profile chart and is the single most actionable metric for a roaster:

• Ideal shape — a smoothly declining curve from the turning point through development
• Crash — a sudden drop in RoR (bean temp nearly stops climbing). Produces baked, flat, doughy flavors
• Flick — a sudden RoR increase after first crack. Creates sharp, roasty, burnt flavors
• Plateau — RoR holds flat too long. Another form of baking

3. Environment Temperature (ET)

Also called drum temperature or air temperature — this measures the environment surrounding the beans rather than the beans themselves. The difference between ET and BT reveals heat transfer dynamics. ET typically runs 10–50°C above BT.

4. Airflow

In roasters with variable airflow (damper control), airflow affects convective heat transfer and the removal of smoke and chaff. Higher airflow increases convective heat but also cools the drum. Profiling airflow changes alongside temperature creates a more complete picture.

Reading a Roast Curve

A standard roast profile chart displays:

• X-axis — time (minutes:seconds)
• Y-axis (left) — temperature in °C (or °F)
• Y-axis (right) — RoR in °C/min
• BT line — an S-shaped curve rising from the turning point to the drop
• RoR line — ideally a smoothly declining curve
• Vertical markers — turning point, yellowing, first crack, drop

Key Profile Milestones

Software Tools

Artisan (free, open-source) - Supports hundreds of roaster models via serial, Modbus, and Phidgets connections - Comprehensive curve analysis, RoR smoothing, and statistical tools - Built-in cupping and roast comparison features - Community-driven development; steep learning curve

Cropster (subscription, $50–150/month) - Cloud-based roast logging with real-time curve display - Multi-location support for commercial roasteries - Green coffee inventory, cupping, and quality management integrated - Industry standard for specialty commercial roasters - Machine learning suggestions for profile optimization

RoastTime (free, Aillio Bullet-specific) - Designed specifically for the Aillio Bullet home/prosumer roaster - Real-time control of power, fan, and drum speed - Community roast sharing via Roast.World platform

Building a Profile Library

Professional roasters maintain a profile library — a collection of tested, approved profiles organized by origin, variety, process, and intended brew method:

1. Baseline profile — a starting point for each green coffee, based on density, moisture, and lot size
2. Exploration profiles — variations on the baseline with adjusted charge temperature, gas settings, airflow, and development time
3. Production profile — the final, approved profile that is replicated for every batch of that coffee

Practical Tips for Better Profiles

• Start with the RoR — a smoothly declining RoR from 10–12°C/min at the turning point to 4–6°C/min at the drop is a reliable framework for specialty roasting
• Adjust one variable at a time — change only gas, airflow, or charge temp between batches, never all three
• Cup every experiment — the curve means nothing without tasting the result
• Log environmental conditions — ambient temperature and humidity affect roast dynamics; note them
• Compare overlaid curves — software tools let you overlay two profiles to see exactly where they diverge and correlate that with cupping differences