The effect of varying the inlet air temperature over the range from 134 degrees C to 210 degrees C on the degree of crystallinity for spray-dried lactose powders (from similar to 55% crystalline to similar to 76% crystalline) has been studied experimentally in a Buchi-290 laboratory-scale dryer, since the temperature is likely to be important according to the Williams-Landel-Ferry theory for solid-phase crystallization. The increased crystallinity at higher-temperatures has been measured by water-induced crystallisation, X-ray diffraction, modulated differential scanning calorimetry and pore size and volume analysis, with all techniques showing consistent results. The results indicate that the degree of crystallinity in spray-dried products can be controlled by adjusting the operating conditions. (C) 2007 Elsevier Ltd. All rights reserved.