Biotransformations of hop-derived aroma compounds by Saccharomyces cerevisiae upon fermentation

Abstract

Although hops are only added in relatively small amounts at particular stages of the brewing process, they have a high impact on the final beer flavor characteristics. The aroma of raw hops, caused by flavor-active constituents present in hop essential oil, clearly differs from the characteristic hoppy aroma of finished beer. Because of the very complex chemical composition of hop essential oil itself and insufficient knowledge on the many (bio)chemical conversions of hop oil components during the brewing process, the chemical background of hoppy aroma is still ill-defined. Since no reviews about the influence of yeast on hop oil-derived aroma compounds during the fermentation process – and thus the influence of fermentation on the hoppy aroma of final beer- have been spotted, this article was drawn up aiming at a clear overview of scientific research that has already been done in this field and of the current know-how, resulting thereof. Proposed flavor-active constituents for hoppy aroma (terpenes, sulfur compounds and oxygenated compounds) originating from hop essential oil and possible transformations of these compounds during fermentation will be discussed. In addition, the effect of yeast enzymes on hop glycosides will be reviewed, since several investigations point to their high potential as precursors of highly flavor-active aroma compounds that may contribute to the hoppy aroma of beer.