Solutions of 10 wt% solids, reconstituted from three types of dairy powders (milk protein concentrate, calcium caseinate and whey protein concentrate) were sonicated prior to lab scale spray drying at inlet and outlet temperatures of 180 degrees C and 80 degrees C respectively. The aim was to investigate the effects of sonication on the surface composition and morphology of the resulting powders. The effects of storage on the functional behaviour of these powders were also observed over 60 days at 25 degrees C, under two different humidity conditions (23.1% and 75.3%). No significant changes to the surface composition (fat, protein and lactose) of the sonicated and non-sonicated powder samples occurred during storage. The microstructure of non-sonicated powder samples showed the appearance of particle agglomerates upon storage, whereas this was not observed with sonicated samples. Importantly, it is shown that sonication prior to drying can increase powder stability during storage and delay the loss of powder solubility. When powders are reconstituted, the increase in solution viscosity that is normally associated with long term storage is also slowed. This is beneficial to industry where powder stability is important for reconstitution and use in the manufacture of secondary dairy products. (C) 2014 Elsevier Ltd. All rights reserved.