Five mixtures of dried skimmed milk (DSM) and wheat flour (WF) were prepared and stored for 45 days at 20 degrees C and various relative humidities (RH) from 0% to 85%. Morphological properties, particle size distributions and mechanical properties were studied before and during storage. Scanning electronic microscopy (SEM) showed that samples stored at high RH (59-85%) agglomerated and formed a compact mass of powder due to caking phenomenon. The caking intensity increased with storage relative humidity and was expressed as the maximum force (F-max.) calculated from force/compression curves. DSM powders showed stick-slip behaviour during deformation and, moreover, this phenomenon increased with the DSM ratio in the mixture (up to 20 +/- 1N for 100% DSM) and disappeared with storage relative humidity. (c) 2006 Elsevier B.V All rights reserved.