Saccharomyces cerevisiae biodiversity during the brewing process of an artisanal beer: a preliminary study

In this study we investigated the biodiversity of Saccharomyces cerevisiae during the brewing of an artisanal beer, as well as during its storage in the bottle for 107 days at 20°C. After inoculation with an active dried yeast (ADY), the yeast counts were followed during fermentation and after bottling. Yeast loads remained stable at 106 – 107 colony forming units (cfu)/mL, and only after day 21, were they were reduced to 104 cfu/mL. After three months in the bottle they spanned 102 - 105 cfu/mL. Almost all isolated yeasts were identified as S. cerevisiae and after molecular characterization, unexpected results were obtained. The ADY did not to take over the fermentation process and only after 21 days did isolates from the beer share similarities with the inoculated strain. During storage, a high diversity was found, underlining that each bottle developed its own micro-ecosystem. This study highlighted the necessity for better investigations of S. cerevisiae population dynamics during artisanal brewing. Even when the chemical parameters measured confirmed a correct fermentation process, the inoculated strain was not the main yeast involved in the fermentation and consequently, the final product may have different sensory characteristics from the ones expected by the producers.