The kinetics of freeze-drying and temperature changes in the product core have been established for milk and water frozen in vials. The influence of heating plate temperature, working pressure and initial water content on the sublimation kinetics have been studied. The operating pressure is paramount since it causes dehydration speeds to vary by a factor of 1–2. Through the use of a simple model of the ‘uniformly retreating ice front’ type, it has been possible to identify the transfer parameters of the model. Correlations with the operating pressure have been established. The results show a working pressure optimum at 200 Pa.