A closed reaction vessel for fermentation or enzymatic reactions for production of cells and biosynthetic products, which range in size from benchtop fermentors to industrial tanks. Bioreactors allow automatic regulation of the flow of oxygen, culture medium and other nutrients, and maintaining the temperature and pH; they minimise the potential for contamination and can produce a higher density of cells than can be produced in traditional cultures; because of the limited mid-procedure cell access, bioreactors are of limited use in producing cells destined for cell therapy, for which culture bag systems are more popular.