What is ideal charge temperature in roasting?

Charge temperature is the temperature of the roaster drum at the moment green beans are loaded. It is a critical parameter that determines the intensity of the initial thermal shock experienced by the beans, conditions the speed of the drying phase and, by extension, the overall shape of the roast curve. There is no universal charge temperature: it varies with the quantity loaded, bean density and the target sensory profile.

When green beans (typically at 15–25 °C) are poured into a hot drum, the temperature measured by the probe drops sharply — this is the 'turning point' (TP), the moment the curve reaches its minimum before rising again. This phenomenon is due to the thermal inertia of the cold beans absorbing heat from the drum. The higher the charge temperature, the more intense the thermal shock, the lower the turning point, and the faster and more aggressive the subsequent drying phase.

Typical charge temperatures range from 160 °C to 230 °C depending on roasters and machines. A Probat drum roaster used for a 12 kg batch might charge at 190–200 °C for a medium profile; the same roaster loaded with only 6 kg might need a charge at 210–220 °C to compensate for the reduced mass. Specialty roasters adjust the charge according to bean density: high-altitude beans (dense) tolerate higher charges because they require more initial energy for drying; lower-altitude beans (less dense) or dry naturals (less moisture) can start at a lower charge.

The resulting turning point (TP) is itself an important indicator: too high (insufficiently low on the curve), it signals a charge too cold and insufficient drying, risking underdeveloped coffee; too low (very low temperature), it signals excessive thermal shock and too fast a drying phase, risking cracking or irregular surface development. Experienced roasters typically target a TP between 70 and 100 °C, reached 60 to 90 seconds after charge. A lesser-known fact: some experimental roasters pre-warm green beans to 40–50 °C before loading to reduce thermal shock and obtain a more predictable turning point — a non-standard practice but tested by competition professionals.

Charge temperatures and their effects