Fed-batch operations are semi-batch operations in which one or more streams of feed containing nutrient sources, precursors, inducers, and mineral sources are fed either continuously or intermittently during the course of otherwise batch operations. The culture content is harvested either fully or partially at the end of the run and is used as the inoculum for the next cycle. By regulating the feed rates, it is possible to regulate the bioreactor environment to maximize the total rate of production, the reactor productivity, or the product yield.

Many industrially important bioreactor operations involving microbial and animal cells are carried out in fed-batch mode. These so-called fed-batch cultures have been found to be particularly effective for fermentation processes and cell cultures in which it is desirable to overcome such common phenomena as substrate inhibition, catabolite repression, product inhibition, and glucose effects to achieve high cell density for efficient fermentation, to minimize high viscosity effects, and to take advantage of auxotrophic mutants. Products produced by fed-batch cultures include amino acids, antibiotics, enzymes, microbial cells, organic chemicals, polysaccharides, proteins, tissue culture products, and various recombinant DNA products.