Wetting and rehydrating effectively a powder is an important industrial
process for food products, detergents and pharmaceuticals.
The wetting condition leading to the formation of an island of powder at the
surface of a liquid is studied and the effect of grain size distribution,
packing defects and liquid flow are investigated.
The implications for applications are discussed, with a focus on the
rehydration of soluble powders and the formation of powder lumps.