A microcapsule composition comprising a core material in a matrix of polymorphic shell material, releases said core material in an aqueous environment in accordance with zero order linear release profile. A preferred composition comprises a core material having a degree of water solubility entrapped in a beta crystalline matrix of water insoluble shell material which matrix may, optionally, be surrounded by a contiguous core material-free layer of water insoluble shell material. Also disclosed is a process for the preparation of microcapsules comprising subjecting a flowable mixture of core material and a first amount of water insoluble shell material to a pressure force to form a pressure-treated mixture, and passing said pressure-treated mixture through a spray nozzle into a chilling zone to form a solidified composition. A special embodiment of the method providing for the long term moisture stability of the resulting microcapsules subjects the microcapsules prepared in the first step to a second coating with a second amount of water insoluble shell material.