To catalyse is to act as a catalyst: to speed up a chemical reaction without being consumed by it. In food science, enzymes are the great catalysts, from amylases converting starch to sugars in brewing and baking, to rennet coagulating milk in cheesemaking, to the polyphenol oxidases behind browning in cut fruit. Each enzyme lowers the activation energy of its specific reaction, working under mild conditions of temperature and pH that would otherwise need harsh chemistry. Industrial food processing depends on catalysis at every turn, and understanding which enzymes act, and how to control them, is fundamental to product quality.