Fermentation involves microorganisms metabolizing organic compounds and transforming food through chemical and biological processes. Key steps include selecting and maintaining starter cultures, ensuring purity and activity of cultures, and preparing bulk cultures. Microbes undergo homofermentation or heterofermentation pathways when metabolizing sugars like hexoses. They also metabolize proteins through proteolysis and citrate through specific enzymatic pathways. Molds in cheeses further metabolize proteins and lipids through various enzymes and pathways to produce characteristic flavors.