With a highly efcient fed-batch cell culture process, it is quite feasible to feed the equivalent of 400–700mOsm/kg of feeds over the course of 10–18days. With such a process, feeds must be quite concentrated in order to minimize the total vol­ume of liquid added to the culture. Many industrial-scale bioreactors have limits on the total volume that can be fed due to the placement of mixing impellers and the desire not to transition the liquid level through this zone of increased shear with its ensuing potential for increased foam formation. The science (or art!) of preparing very concentrated feed mixtures often relies on the careful order of addition of chemicals, manipulation of pH (up and down) and temperature, and separate prepa­ration of certain concentrated solutions before addition to the bulk feed mixture. In some cases, it may even be necessary or efcient to separate the components into multiple distinct feeds that might not be sufciently stable together in a single solu­tion. Furthermore, the pH manipulations often necessary to get all the components into solution will in turn introduce additional ions to the solution that are not con­sumed by the cells. Such ions, sodium and chloride being the most common of these, will ultimately accumulate in the culture. Some fed-batch culture processes then also need to manage the accumulation of these ions and other cell-produced waste products that might not be toxic in and of themselves, but do contribute to the continuous slow increase in the osmotic strength of the culture until the high osmotic strength itself becomes detrimental to cell health and productivity. While probably not yet necessary for the vast majority of fed-batch cultures, our laboratory, in con­sultation with drug product formulation experts, has also experimented with the lyophilization and even sterile spray-drying of cell culture feed media. Lyophilization was found to be largely impractical due to the amounts of high osmotic strength excipients that need to be added to facilitate stable cake formation. Aseptic spray drying, however, was found to produce a very stable and incredibly fast dissolving, uniform particle size powder that can be added directly to the surface of a produc­tion bioreactor. Naturally, methods of addition of an aseptic dry powder to the liquid surface of a bioreactor would then need to be worked out before practical imple­mentation. Should much higher efciency cell lines and cell culture processes be developed in the future, dry feeds might inevitably increase overall bioreactor pro­ductivity by minimizing culture volume increases.