Brewing potential of the wild yeast species Saccharomyces paradoxus

Saccharomyces paradoxus is commonly isolated from environmental samples in Northern Europe and North America, but is rarely found associated with fermentation. However, as novelty has become a selling point in beer markets, interest toward non-conventional and local yeasts is increasing. Here, we report the first comprehensive investigation of the brewing potential of the species. Eight wild strains of S. paradoxus were isolated from oak trees growing naturally in Finland, screened in a series of fermentation trials and the most promising strain was selected for lager beer brewing at pilot scale (40 l). Yeasts were evaluated according to their ability to utilize wort sugars, their production of flavour-active aroma volatiles, diacetyl and organic acids, and sensorial quality of beers produced. All strains could assimilate maltose but this occurred after a considerable lag phase. Once adapted, most wild strains reached attenuation rates close to 70%. Adaptation to maltose could be maintained by re-pitching and with appropriate handling of the adapted yeast. Fermentation at 15 °C with the best performing strain was completed in 17 days. Maltose was consumed as efficiently as with a reference lager yeast, but no maltotriose use was observed. Bottled beers were evaluated by a trained sensory panel, and were generally rated as good as, or better than, reference beers. S. paradoxus beers were considered full-bodied and had a relatively clean flavour profile despite the presence of the clove-like 4-vinyl guaiacol. In conclusion, S. paradoxus exhibits a number of traits relevant to brewing, and with appropriate handling could be applied industrially