Rate of Rise (RoR) Curve

The Rate of Rise (RoR) curve is perhaps the most important metric for a professional roaster. It represents the change in bean temperature over a specific interval of time, usually measured in degrees per minute. By visualizing this data on a roast profile software, a roaster can see exactly how much energy is being applied to the beans at any given moment, allowing for precise adjustments to gas, airflow, and drum speed.

In the early stages of the roast, the RoR is typically high as the beans absorb heat to evaporate moisture. As the roast progresses into the Maillard reaction and caramelization phases, the roaster aims to manage the RoR to ensure the coffee develops properly. A common goal is a 'declining' RoR, where the rate of temperature increase gradually slows down as the beans approach the end of the roast. This prevents the exterior of the bean from burning before the interior is fully developed.

If the RoR drops too sharply, the coffee may become 'baked,' resulting in flat, dull flavors. Conversely, if the RoR spikes or 'flicks' at the end of the roast, it can lead to uneven development or scorched beans. Monitoring the RoR curve allows the roaster to avoid these common defects and achieve a consistent, high-quality result across different batches.

In practice, the RoR curve is the roaster's roadmap. It tells the story of the roast's energy management. When a roaster talks about 'stretching' the development time or 'crashing' the roast, they are referring to manipulations of the RoR. For the consumer, a well-managed RoR means a coffee that is sweet, vibrant, and free from the harsh, underdeveloped, or burnt notes that occur when the energy application is poorly controlled.