During spray drying of milk droplets, pure moisture evaporates rapidly from the droplet surface in the constant-rate drying period. The droplet temperature naturally stabilizes at the wet-bulb temperature of the drying air (typically $40^\circ\text{C} - 50^\circ\text{C}$), protecting heat-sensitive milk proteins even though the drying air dry-bulb temperature is $180^\circ\text{C} - 200^\circ\text{C}$.