The most frequently used technique for dehydration of dairy products is spray drying. This is an effective method for preserving biological products as it does not involve severe heat treatment and it allows storage of powders at an ambient temperature. Due to the variety and complexity of the concentrates to be dried, a more rigorous understanding of spray drying based on physico-chemical and thermodynamic properties has now become necessary. However, the current state of the art and knowledge do not allow determination of the parameters of spray drying of dairy products. The only way to determine these parameters is to perform several complex and expensive experiments with spray dryer pilots. In this study, a new method was developed to evaluate the ratio of bound to unbound water by using drying by desorption. The results, combined with thermodynamic and physico-chemical parameters (such as, absolute and relative humidity of air, total solids and temperature of concentrate, and air flow rate), provide more precise determination of certain spray drying parameters such as inlet air temperature and mass flow rate. More than 50 experiments were performed to correlate calculated and measured parameters in a pilot plant (Bionov) using water, skim milk, infant formula milk, caseinate maltodextrin and other food concentrates. The results showed that the difference between the calculated and measured inlet air temperature was less than 5%, the determination coefficient being close to 0.96. The economic value of this system is obvious, because it is easy to anticipate the spray drying parameters by using a controller integrating the water availability of the concentrate and certain thermodynamic parameters. Software based on this step was developed (SD(2)P (R), spray drying parameter simulation and determination) and registered at the APP (Association pour la Protection des Programmes). (C) 2008 Elsevier Ltd. All rights reserved.