We are developing cost-effective, sustainable, and environmentally-friendly processes for the production of 15-carbon sesquiterpenes using metabolically-engineered Saccharomyces cerevisiae. These compounds are generally produced in plants and serve a diversity of protective functions. They are responsible for the distinct flavors and fragrances associated with plants, can be anti-fungal or anti-viral agents, or can act as insect attractants and repellents. Accordingly, terpenes have significant commercial value to the flavor and fragrance, urban pesticide, crop protection, and pharmaceutical industries. Their rarity, however, makes sesquiterpenes expensive to extract, and because they are multicyclic and multichiral, they are difficult and expensive to synthesize. Our first commercial sesquiterpene product is nootkatone, which is responsible for the distinctive flavor and fragrance of grapefruit. Its current market is limited by cost to beverages and high-end fragrances, but other potential markets will be accessible when it is available at lower cost. Our method of making nootkatone begins with the production of valencene using a S. cerevisiae strain containing a highly efficient protein-engineered citrus valencene synthase (CVS) enzyme. This valencene is then oxidized, either biologically or chemically, to produce nootkatone. Using this valencene producing strain, large-scale production has been achieved.