Different materials appear to crystallize to varying extents inside spray dryers. By comparing the characteristic time scales for both nucleation and crystal growth with sodium chloride and lactose, it is possible to get some insight into why these differences occur. Differences in growth rates during the crystallization step and to glass-transition temperatures during the amorphous to crystalline transition may be the key effects here. The advantages and disadvantages of crystallizing different materials inside spray dryers are also considered, and reasons for not finding crystallization in many spray-dried dairy powders are discussed, with the presence of proteins and other components in milk slowing down the crystallization step. (C) 2008 Elsevier Ltd. All rights reserved.