In-Depth Guide: Rate of Rise (ROR) in Coffee Roasting

Introduction to Rate of Rise (ROR)
Rate of Rise (ROR) is one of the most essential metrics in coffee roasting. It measures how quickly the temperature of the beans increases over time—usually expressed in °C or °F per minute. For roasters, ROR acts like a real-time performance gauge, helping to adjust heat and airflow for ideal flavor development. Controlling ROR helps avoid common roasting flaws like scorching or underdevelopment, both of which can drastically affect cup quality.

The Science Behind ROR

ROR is driven by the principles of thermodynamics. During roasting, coffee beans go through both endothermic (heat-absorbing) and exothermic (heat-releasing) stages. The rate at which heat penetrates the beans influences critical chemical reactions like the Maillard reaction and caramelization. A well-controlled ROR ensures energy is evenly distributed, minimizing the risk of baked or grassy flavors.

Stages of Roasting and ROR Management

1. Drying Phase (up to 150°C / 302°F)
Goal: Remove moisture (~10–12% weight loss)

ROR Strategy: Start with a high ROR (15–25°C/min) to drive off water efficiently. Be cautious—too much heat can scorch the bean surface.

2. Maillard Reaction Phase (150–190°C / 302–374°F)

Goal: Initiate browning and flavor complexity

ROR Strategy: Taper down the ROR (8–12°C/min) to extend this phase. A gradual decline enhances sweetness and body, while sudden spikes can introduce bitterness.

3. Development Phase (post-first crack)
Goal: Build final flavor profile

ROR Strategy: Maintain a lower, steady ROR (4–8°C/min). Too high can burn the coffee; too low risks baked flavors and muted notes.

How to Measure and Monitor ROR

Hardware: Thermocouples placed in the bean mass capture temperature data.

Software: Tools like Cropster or Artisan graph the ROR curve in real time.

Formula: ROR = Temperature change ÷ Time. Many roasters use 30-second averaging to reduce curve noise, though this can slightly delay feedback.

Probe Placement: Crucial for accuracy—improper placement skews temperature readings and misguides adjustments.

Understanding ROR Curves

A typical ROR curve should decline smoothly throughout the roast. Watch out for:

Crashes: Sudden drops in ROR indicate stalled energy transfer—usually due to overly reduced heat. This often leads to flat, dull coffee.

Flicks: Sharp spikes often result from overcompensating with heat. These can cause scorched or harsh notes.

Plateaus: May stall flavor development if sustained too long.

Keep in mind: ambient humidity, green bean density, and roaster type (drum vs. fluid bed) all influence how ROR behaves.

Adjusting ROR: Practical Techniques
Heat Application: Make gradual, measured changes to your burner or heat source. Sharp changes lead to curve instability.

Airflow Control: Boost airflow to reduce heat buildup; lower it to trap more heat and maintain ROR.

Development Time Ratio (DTR): A key metric—this is the time after first crack divided by total roast time. Aim for a DTR of 20–25% for light roasts.

Common ROR Challenges and Fixes

Inconsistent Roast Results: Check and calibrate probes regularly. Document ambient variables like humidity and room temp.

Equipment Behavior: Drum roasters change temperature more gradually, while fluid bed roasters respond faster. Tailor your adjustments accordingly.

Baked Flavors: Often caused by low ROR during development. Apply more heat earlier to maintain momentum.

Best Practices for ROR Management

Begin with a High ROR: Jumpstart the roast, then slowly back off to avoid overdevelopment.

Plan for the Exothermic Shift: After yellowing (~160°C), beans release their own heat. Reduce burner settings early to avoid ROR spikes.

Log Everything: Track temperature, ROR, roast duration, and sensory feedback. Over time, these logs will help you perfect your approach.

Case Study: Roasting a Colombian Gesha
A roaster working with Colombian Gesha found grassy notes in early roasts. By reducing the Maillard phase ROR from 12°C/min to 8°C/min and maintaining a steady 5°C/min during development, they revealed the bean’s floral and fruity complexity—producing a cup rich in jasmine and peach.

Expert Opinions on ROR

Scott Rao, author of The Coffee Roaster’s Companion, recommends a steadily declining ROR to avoid baked flavors. That said, some roasters successfully use controlled plateaus during the Maillard phase to build body and sweetness. There’s no one-size-fits-all—context matters.

Mastering ROR is a blend of science and intuition. By understanding heat dynamics, chemical reactions, and the behavior of your roasting equipment, you can manipulate ROR to consistently deliver exceptional coffee. Every bean is different, and the journey of experimentation never ends.

Further Reading & Resources

The Coffee Roaster’s Companion by Scott Rao

Roast Magazine case studies on ROR profiles

Professional workshops on probe calibration and roast logging