This study demonstrated the feasibility of applying an ultrasound test to evaluate the ability of a powder to interact with a solvent and thus to predict the reconstitution behaviour of powders. The ultrasound attenuation was monitored and a corresponding relaxation time was calculated. Analysis of the ultrasound signal and images obtained by a granulomorphometer in the course of dispersion showed that the time required by the ultrasound attenuation parameter to relax is strongly associated with the time required by the solvent to penetrate primary particles. It was also shown that this step is of crucial importance in the dissolution mechanism as it precedes the fragmentation phase, identified as a limiting step. Classification of dairy powders according to their relaxation times (ultrasound test) and rehydration times (rehydration test, calculated with Static Light Scattering) was in good agreement for the range of milk powders investigated. Industrial relevance: Spray drying is commonly used to produce dairy powders in the food industry. Although the rehydration of these powders can be very slow, few analytic methods are available to evaluate the dissolvability of a dairy powder; consequently, there is a current lack of guidelines in order to tune spray dryer operating parameters for improving instant properties. The objective of this study is to present a new analytical method based on ultrasound test to evaluate powder ability to reconstitute. A probe was immerged in the liquid and the transmitted signal was analysed during the course of rehydration. The acoustic test was demonstrated to be effective in tracking solvent interactions, making it possible to assess the ability of a solvent to bind with the primary particle, and thus revealing it to be a powerful tool to evaluate the reconstitution ability of dairy powder quickly with low material costs. Of course the scope of this tool is broader than the sole food sector and encompasses all applications requiring a reconstitution step in a solvent.