Rate of Rise

Rate of Rise (RoR) represents the derivative of the bean temperature curve over time, functioning as a real-time indicator of how quickly heat is being transferred into the coffee beans. While the bean temperature (BT) curve shows the current state of the roast, the RoR curve acts as a predictive tool, showing the velocity of that temperature change. By monitoring this speed, roasters can manage the energy input throughout the drying, browning, and development phases to ensure the desired chemical transformations occur without stalling or overheating.

The concept gained prominence in specialty coffee through the work of experts like Scott Rao, who established the declining RoR model as a standard for quality. In this model, the RoR peaks early—typically within the first few minutes after the turning point—and then gradually declines for the remainder of the roast. This steady, controlled deceleration is intended to prevent the roast from stalling, which can lead to 'baked' coffee, characterized by a flat, cardboard-like finish and a lack of sweetness.

In practice, RoR is calculated by measuring the difference in temperature between two set intervals. After the beans are charged into the roaster, the temperature initially drops due to the cooling effect of the room-temperature beans. The point where the temperature stops falling and begins to rise is known as the turning point. Following this, the RoR should ideally show a smooth, continuous decline. If the RoR drops too sharply or hits zero before the end of the roast, it is often referred to as a 'crash,' while a sudden, late-stage spike is known as a 'flick.'

These anomalies are critical to avoid because they indicate an imbalance in heat transfer. A crash often results in underdeveloped, sour, or hollow flavors, as the beans fail to reach the necessary internal temperature to fully caramelize sugars and break down acids. Conversely, a flick can introduce burnt or smoky notes by applying excessive heat at the end of the process. By tracking the RoR on software like Artisan or Cropster, roasters can make micro-adjustments to airflow, drum speed, or gas pressure to keep the curve on its intended trajectory.

For the farmer and the producer, understanding how different processing methods—such as naturals versus washed coffees—affect heat absorption is essential. Certain high-density or naturally processed beans may require specific adjustments to the RoR to prevent the roast from stalling during the first crack. Because moisture content and bean density vary, the RoR provides a universal language for roasters to adapt their profiles to the specific physical characteristics of the green coffee they are working with.

Ultimately, the RoR is a tool for consistency and flavor control. It allows a roaster to replicate a successful profile across different batches by ensuring the energy application remains identical. For the drinker, a well-managed RoR is the difference between a vibrant, complex cup that highlights the coffee's origin and a dull, one-dimensional experience. As the industry continues to refine its understanding of thermodynamics in roasting, RoR remains the primary metric for diagnosing the success of a roast profile.