A penetration test measuring the force required to penetrate a milk powder sample and an attrition test of caked milk powder samples in a roll mill were used to characterize the cake formation of skim milk powders. The influences of temperature and pressure on the time required to form a milk powder cake were determined using these techniques. It has been found that the cake formation time was increased with decreasing temperature and pressure on the milk powder samples. An empirical equation was developed in order to predict the caking time of the milk powders samples as a function of temperature and pressure the samples were exposed to. (C) 2003 Elsevier Science Ltd. All rights reserved.