Fermentation

Fermentation, whose name comes from the Latin fervere ('to boil') - a reference to the visible bubbling caused by gas release - is the anaerobic metabolic breakdown of organic molecules, typically glucose, into acids, gases or alcohol, carried out by bacteria and fungi that are adapted to live without oxygen or a working electron-transport chain. It took until 1856 for Louis Pasteur to formally establish that living yeast cells, not a purely chemical process, were responsible, founding the field now called zymology. Industrially, fermentation is scaled up inside a bioreactor (fermentor): a vessel engineered to hold a precisely controlled environment - aeration, agitation, temperature and pH - in which microorganisms, cells or isolated enzymes act on a substrate to generate a desired product. Running a fermentation splits naturally into two phases. The upstream process covers everything done before the fermenter actually starts - sterilising the vessel, preparing and sterilising the growth medium, and building up a healthy inoculum culture. The downstream process covers everything after fermentation finishes: distillation, centrifuging, filtration and solvent extraction, whose combined job is essentially purifying the raw fermentation broth into the finished product. Industrially, fermentation delivers four broad categories of value: microbial biomass itself (grown, dried and used as single-cell protein); primary metabolites needed for the microbe's own survival (ethanol, citric acid, lactic acid, acetic acid) versus secondary metabolites that are not essential to the microbe but are commercially valuable (antibiotics like penicilli …