Abstract
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.
Highlights
IntroductionBesides the already mentioned S. cerevisiae, S. eubayanus and S. paradoxus, the genus currently consists of five other species: S. arboricola, S. jurei, S. kudriavzevii, S. mikatae, and S. uvarum [16,17,18,19,20,21]
The sequencing reads of 30 isolates were identical to each other having a 100% query coverage and 100% identity with the best hit, Saccharomyces paradoxus NRRL Y-17217, in a BLAST search of the NCBI Nucleotide database
The single colony from YPD plate was propagated in liquid YPD and the colony on YNB–maltose plate was propagated in YPM prior to fermentations
Summary
Besides the already mentioned S. cerevisiae, S. eubayanus and S. paradoxus, the genus currently consists of five other species: S. arboricola, S. jurei, S. kudriavzevii, S. mikatae, and S. uvarum [16,17,18,19,20,21]. The genus has a worldwide distribution, but species-specific differences exist: S. arboricola and S. mikatae have not been isolated outside of Asia, and S. eubayanus has not yet been found in Europe. It has been proposed that oak is a natural niche [5], but there is often a sampling bias toward oak trees, and the Saccharomyces yeasts have been isolated elsewhere as well; Goddard and Greig [25] have proposed that the species S. cerevisiae, for example, could be nomadic by nature, i.e. found in low abundance in many different niches. Saccharomyces cerevisiae and Saccharomyces paradoxus are both found in Europe, but apparently, the small deviation in optimal growth temperature enables the latter to inhabit cooler parts of Europe, making it the only natural wild Saccharomyces species found in northern Europe to date [26]
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