Alexander Lauterbach (1), Jürgen Behr (1), Mathias Hutzler (2), Tim Meier-Dörnberg (2), Rudi F. Vogel (1); (1) Lehrstuhl für Technische Mikrobiologie, Technische Universität München, Freising, Germany; (2) Forschungszentrum Weihenstephan für Brau- und Lebensmittelqualität, Freising, Germany

Yeast, Fermentation, and Microbiology

Craft beers brewed with different types of malts and new hop varieties get flavors ranging from passion fruit and lemon to coffee and chocolate. Brewing innovative beers with a unique flavor should also be possible using different brewing yeasts, but their selection is currently based on elaborate processes along trial and error. Generally, the top-fermenting brewing yeast Saccharomyces cerevisiae is more versatile with respect to its aroma formation potential compared with the bottom-fermenting yeast S. pastorianus. The beers produced with top-fermented yeast strains display different sensorial characteristics. Currently there is a lack of fast, cost-effective and simple methods to characterize brewing yeasts and aromatic impression matrix assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–TOF MS) may be suitable to close this gap. In this proof-of-concept study we aimed at the establishment of a correlation of sensorial impact of a yeast on a beer as determined by sensorial analysis with the sub-proteome pattern expressed by this yeast as determined by MALDI-TOF MS. Therefore, the mass spectra of top-fermenting yeasts strains were recorded upon optimized sample preparation and analyzed by multidimensional scaling. Analysis of 1,380 samples (46 yeast strains) demonstrated that differentiation of top- and bottom-fermenting brewing yeasts, as well as grouping S. cerevisiae strains by beer type (wheat beer, ale, Altbier, Kölsch), is possible. Concomitantly, we investigated the fermentation and maturation of standardized wort with top-fermenting brewing yeast strains and evaluated their aroma profile by numerous different tasting schemes. All beer samples were tasted and judged by a trained sensory panel of DLG-certified tasters (Deutsche Landwirtschafts-Gesellschaft e.V.). Thereby, the beers obtained with the tested brewing yeasts were compared to those of reference strains frequently used in the brewing industry. Interestingly, 83% of the tested beers in sensorial analysis correlated with those of the MALDI-TOF MS groupings. While differentiation of most beer styles obtained with different yeast types was achieved, the testing panel had problems differentiating between beers produced with predicted Altbier and Kölsch strains. Furthermore, the sensorial testing identified a clove flavor (POF+) for an ale yeast strain instead of a predicted fruity flavor. The clove flavor can also be correlated to typical MALDI-TOF MS patterns. Taken together, MALDI-TOF MS recommends itself for fast sensotyping of brewing yeasts and as a powerful tool for exploitation of new yeast strains, enabling a focus of empirical development of promising strains.

Alexander Lauterbach was born in 1987 in Wiesbaden, Hessen, Germany. In 2011 he received a B.S. degree in food science and biotechnology from the University Hohenheim. He started an internship at the Heidelberger brewery to work in different areas, like production and quality assurance, and attended a malting industry. After the internship he finished his studies, completing an M.S. degree in brewing and beverage technology at the Technische Universität München. At the moment he is working on his Ph.D. degree at the Chair of the Technische Mikrobiologie under the supervision of Prof. Rudi F. Vogel at Technische Universität München. He characterizes and analyzes brewing yeasts of the genus Saccharomyces by MALDI-TOF MS and bioinformatics. Apart from his scientific work, he received a certificate as a sensorial tester for beer and mixed beer beverages along the guidelines of Deutsche Landwirtschafts Gesellschaft e.V. (DLG).