Modern roasting requires precise convective to conductive ratios. Higher fan speed (static pressure in pascals) shifts the energy mix to forced convection, driving heat to the bean core rapidly without risking surface scorching or structural tipping. (1/3) 🧵 Each bean is insulated by a stagnant boundary layer of air and moisture. High velocity convective airflow thins this layer to reduce thermal resistance. Too much velocity, however, strips heat from the drum environment, stalling the rate of rise. (2/3)