AUTHOR=Hutzler Mathias , Michel Maximilian , Kunz Oliver , Kuusisto Tiina , Magalhães Frederico , Krogerus Kristoffer , Gibson Brian 

TITLE=Unique Brewing-Relevant Properties of a Strain of Saccharomyces jurei Isolated From Ash (Fraxinus excelsior)

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.645271

DOI=10.3389/fmicb.2021.645271

ISSN=1664-302X

ABSTRACT=<p>The successful application of <italic>Saccharomyces eubayanus</italic> and <italic>Saccharomyces paradoxus</italic> in brewery fermentations has highlighted the potential of wild <italic>Saccharomyes</italic> yeasts for brewing, and prompted investigation into the application potential of other members of the genus. Here, we evaluate, for the first time, the brewing potential of <italic>Saccharomyces jurei</italic>. The newly isolated strain from an ash tree (<italic>Fraxinus excelsior</italic>) in Upper Bavaria, Germany, close to the river Isar, was used to ferment a 12°P wort at 15°C. Performance was compared directly with that of a reference lager strain (TUM 34/70) and the <italic>S. eubayanus</italic> type strain. Both wild yeast rapidly depleted simple sugars and thereafter exhibited a lag phase before maltose utilization. This phase lasted for 4 and 10 days for <italic>S. eubayanus</italic> and <italic>S. jurei</italic>, respectively. <italic>S. eubayanus</italic> utilized fully the available maltose but, consistent with previous reports, did not use maltotriose. <italic>S. jurei</italic>, in contrast, utilized approximately 50% of the maltotriose available, making this the first report of maltotriose utilization in a wild <italic>Saccharomyces</italic> species. Maltotriose use was directly related to alcohol yield with 5.5, 4.9, and 4.5% ABV produced by <italic>Saccharomyces pastorianus</italic>, <italic>S. jurei</italic>, and <italic>S. eubayanus</italic>. Beers also differed with respect to aroma volatiles, with a high level (0.4 mg/L) of the apple/aniseed aroma ethyl hexanoate in <italic>S. jurei</italic> beers, while <italic>S. eubayanus</italic> beers had a high level of phenylethanol (100 mg/L). A trained panel rated all beers as being of high quality, but noted clear differences. A phenolic spice/clove note was prominent in <italic>S. jurei</italic> beer. This was less pronounced in the <italic>S. eubayanus</italic> beers, despite analytical levels of 4-vinylguaiacol being similar. Tropical fruit notes were pronounced in <italic>S. jurei</italic> beers, possibly resulting from the high level of ethyl hexanoate. Herein, we present results from the first intentional application of <italic>S. jurei</italic> as a yeast for beer fermentation (at the time of submission) and compare its fermentation performance to other species of the genus. Results indicate considerable potential for <italic>S. jurei</italic> application in brewing, with clear advantages compared to other wild <italic>Saccharomyces</italic> species.</p>