What is fermentation and what are its main types?

Fermentation is a bioprocess where microorganisms convert substrates into desired products under controlled conditions. The main types are: batch fermentation (closed system, all nutrients added initially), fed-batch (nutrients added during cultivation to extend growth and production), continuous fermentation (constant feed and harvest maintaining steady state), and perfusion (cells retained while medium is exchanged). Selection depends on product type, cell characteristics, and process economics. Fermentation is used to produce antibiotics, enzymes, organic acids, biofuels, and recombinant proteins.