Roasting is fundamentally a heat transfer process involving conduction, convection, and radiation. Conduction occurs when beans contact hot drum surfaces, convection through hot air movement, and radiation from infrared energy inside the roasting chamber.
Different roaster designs emphasize different mechanisms. Drum roasters rely more on conduction and convection, while fluid-bed roasters rely almost entirely on convection. The balance of heat transfer affects rate of rise, development, and defect formation.
Uneven heat transfer causes tipping, scorching, or baked flavors. Proper airflow management ensures uniform bean temperature and consistent chemical reactions. Understanding heat transfer allows roasters to control roast momentum rather than reacting to it.