Turning Point

When you ask, 'what is the turning point in coffee roasting,' you are looking at the moment of thermal equilibrium. When cold green coffee beans are dropped into a hot roasting drum, they immediately absorb heat from the environment, causing the temperature probe to register a sharp drop. The turning point is the exact moment this downward trend stops and the temperature begins to climb again.

On most commercial drum roasters, this typically occurs 60 to 90 seconds after the charge, often at temperatures between 75°C and 100°C. The turning point is a vital indicator of the roaster's initial energy management. If the turning point is too low, the roast may struggle to gain momentum, leading to a 'baked' or flat-tasting coffee. If it is too high, the exterior of the beans may scorch before the center has a chance to develop.

Roasters monitor the turning point to ensure consistency across batches. By tracking the time and temperature at which this occurs, a roaster can determine if their charge temperature or drum speed needs adjustment. It serves as the baseline for the rest of the roast curve, signaling that the beans have successfully transitioned from the initial cooling effect of the charge to the active, exothermic-ready phase of the roast.

In practice, the turning point is the first major milestone in a roast profile. It tells the roaster whether they have enough energy stored in the drum to drive the roast through the drying and Maillard phases effectively. For the drinker, a well-managed turning point contributes to a clean, vibrant cup, as it prevents the early-stage defects that can occur when a roast starts on the wrong foot.