Unique Brewing-Relevant Properties of a Strain of Isolated From Ash ().

The successful application of and in brewery fermentations has highlighted the potential of wild 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 . The newly isolated strain from an ash tree () 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 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 and , respectively. utilized fully the available maltose but, consistent with previous reports, did not use maltotriose. , in contrast, utilized approximately 50% of the maltotriose available, making this the first report of maltotriose utilization in a wild species. Maltotriose use was directly related to alcohol yield with 5.5, 4.9, and 4.5% ABV produced by , , and . Beers also differed with respect to aroma volatiles, with a high level (0.4 mg/L) of the apple/aniseed aroma ethyl hexanoate in beers, while 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 beer. This was less pronounced in the beers, despite analytical levels of 4-vinylguaiacol being similar. Tropical fruit notes were pronounced in beers, possibly resulting from the high level of ethyl hexanoate. Herein, we present results from the first intentional application of 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 application in brewing, with clear advantages compared to other wild species.