Engineering industrial brewing yeast for flavor production

Yeast has been used by various peoples for thousands of years to make beer, wine, and other alcoholic beverages. During fermentation, yeast impart a host of flavor and aroma molecules to wine and beer, derived from both central and secondary metabolism. Many of these compounds are derived from the interactions between yeast enzymes and compounds contributed by hops, in the case of beer, and grapes, in the case of wine. The field of metabolic engineering has opened up new avenues for flavor production in microbes such as yeast. In addition to the overexpression or deletion of yeast endogenous enzymes responsible for flavor modulation, de novo production of flavors in yeast is also possible. In the work presented in this doctoral dissertation I describe how these tools have been applied to the engineering of brewer’s yeast strains in order to reduce, and perhaps eventually replace, aromatic hop additions used in the brewing process. Chapter 1 presents a review of genetically engineered brewing and wine yeasts. Commercial and academic examples are discussed. Traits that have been engineered encompass flavor production and off-flavor reduction, flocculation, sugar consumption, and other fermentation performance characteristics. Chapter 2 presents my work engineering California Ale Yeast to biosynthesize the compounds linalool and geraniol, which impart hoppy flavor and aroma to beer. At least one engineered strain was shown to produce beer perceived as hoppier than traditionally hopped beer by a sensory panel in a double-blind tasting. Chapter 3 describes additional engineering of the monoterpene-producing strains and suggests future work to more fully reconstitute the complex flavor imparted by traditional hop additions. Engineered strains provide an avenue for improvement and innovation of the brewing process by making it possible to generate new and distinctive flavors with consistency and reproducibility