Abstract: A porous container for controllably releasing various substances into surrounding fluid environments includes a porous material having pores sized and configured to allow the substances contained within the container to pass through the pores at a rate of no more than about 0.5 g/day/cm2. In a particular embodiment, the porous container is adapted to controllably release microorganisms into surrounding fluid environments, which microorganisms may be cultured within the porous container. The porous container may also be utilized with a variety of dispensing vessels to obtain desired controlled release characteristics.