Yeast : the soul of beer’s aroma—a review of flavour-active esters and higher alcohols produced by the brewing yeast

Among the most important factors influencing beer quality is the presence of well-adjusted amounts of higher alcohols and esters. Thus, a heavy body of literature focuses on these substances and on the parameters influencing their production by the brewing yeast. Additionally, the complex metabolic pathways involved in their synthesis require special attention. More than a century of data, mainly in genetic and proteomic fields, has built up enough information to describe in detail each step in the pathway for the synthesis of higher alcohols and their esters, but there is still place for more. Higher alcohols are formed either by anabolism or catabolism (Ehrlich pathway) of amino acids. Esters are formed by enzymatic condensation of organic acids and alcohols. The current paper reviews the up-to-date knowledge in the pathways involving the synthesis of higher alcohols and esters by brewing yeasts. Fermentation parameters affecting yeast response during biosynthesis of these aromatic substances are also fully reviewed.Eduardo Pires gratefully acknowledges the Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) for the PhD fellowship support (SFRH/BD/61777/2009). The financial contributions of the EU FP7 project Ecoefficient Biodegradable Composite Advanced Packaging (EcoBioCAP, grant agreement no. 265669) as well as of the Grant Agency of the Czech Republic (project GACR P503/12/1424) are also gratefully acknowledged. The authors thank the Ministry of Education, Youth and Sports of the Czech Republic (MSM 6046137305) for their financial support

Ca isotope fingerprints of early crust-mantle evolution

Among the most important factors influencing beer quality is the presence of well-adjusted amounts of higher alcohols and esters; as well as the successful reduction of undesirable by-products such as diacetyl. While higher alcohols and esters contribute rather positively to the beer aroma, diacetyl is mostly unwelcome for beer types with lighter taste. Thus, the complex metabolic pathways in yeast responsible for the synthesis of both pleasant and unpleasant by-products of fermentation were given special attention in this last chapter