Enzyme immobilisation — covalent attachment, entrapment, cross-linking, or adsorption onto solid supports — allows the enzyme to be retained in the reactor while product flows through. Benefits: (1) reuse over many cycles (greatly reduces enzyme cost per kg product), (2) ease of product-enzyme separation, (3) potential improvement in stability. Industrial examples: glucose isomerase (immobilised, for HFCS production), lactase, penicillin acylase, and lipases for biodiesel.