The relative extent of crystallization for lactose and sucrose within spray dryers allows the WLF equation to be tested for this type of in-process crystallization, since this equation suggests that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature of that particular material. In this study, the amount of sucrose crystallization during drying was studied using a bench-top spray dryer (Buchi B290) over a practical range of inlet gas temperatures (95–220 °C). It has been found that very large changes in the degree of crystallinity for the final spray-dried product can be achieved for sucrose by using different inlet gas temperatures, compared with much smaller changes in the crystallinity of lactose for a similar range of inlet temperatures. This result supports the suggestion that the crystallization rate is related to the difference between the material temperature and the glass-transition temperature, since sucrose has a much lower glass-transition temperature than lactose. The results have the potential to be implemented to achieve specified degrees of crystallinity in many powder materials produced from spray-drying processes.