Μελέτη της εξέλιξης του αρωματικού προφίλ ζύθων κατά την πάροδο δύο ετών

Abstract

Different yeast strains can produce beer with a unique and very complex aroma and flavor profile. Using non-conventional yeast gives brewers an unparalleled selling point to differentiate themselves. The purpose of this research was to study the aroma profile of beers produced by a non-Saccharomyces yeast strain and its evolution over time, in both pure and mixed cultures compared to a Saccharomyces cerevisiae yeast strain. Thus, a Pale Ale beer production was carried out and fermented with pure cultures of S. cerevisiae, T. delbrueckii and a mixed culture of the aforementioned yeasts at a 1:10 ratio at 20 οC. After fermentation the produced beers were bottled unfiltered and were stored at 13 οC. Samples were collected after seven days, six, twelve and twenty-four months of maturation, and were analysed by GC-MS for determining their aromatic profile. Compounds from the group of higher alcohols, acids and their esters have been quantified. From the group of higher alcohols, phenyl ethyl alcohol was detected in higher concentration in the mixed culture compared to either monoculture fermentations. The evolution of this compound increased during aging, and after 24 months the beer produced with the mixed culture had the utmost concentration. Moreover, isoamyl acetate and phenyl ethyl acetate were detected in higher concentration in beer produced with T. delbrueckii whereas the concentration in the mixed culture was enhanced after twelve months of maturation. Ethyl hexanoate was present in the T. delbrueckii beers already after seven days, whereas in the S. cerevisiae ones, only after 24 months. The strains were also examined for their production of phenolic compounds, providing a POF character in the final product. After six months, new compounds were detected, such as butanoic, decanoic and dodecanoic acids and their esters. Additionally, the sensory profile of the beers was assessed, and the product of the non-Saccharomyces yeast was evaluated as more fruity, with floral aromatic profile. The beer fermented by the mixed culture showed similar sensory characters to the S. cerevisiae fermentation one.