What is a roast curve in coffee roasting?

A roast curve is a graph that plots temperature against time during a roasting session, showing how the temperature inside the roaster changes from the moment beans are loaded to the moment they drop into the cooling tray. It is the primary visual tool for understanding, analysing, and reproducing roast profiles.

A typical roast curve shows at least two lines: bean temperature (BT), which tracks the heat absorbed by the coffee, and environmental or air temperature (ET), which reflects the roasting atmosphere surrounding the beans. The shape of the bean temperature curve - how steeply it rises, where it plateaus, how it progresses through yellowing, first crack, and drop - captures every meaningful decision made during that roast.

Roasting software such as Cropster, Artisan, and RoasTime record and display roast curves in real time, allowing roasters to compare each batch against a reference profile. Overlaying multiple roast curves reveals whether a profile is being executed consistently or drifting batch to batch. For home roasters moving from instinctive to data-driven roasting, learning to read a roast curve is one of the highest-leverage skills available - it turns a sensory art into something repeatable and improvable.