Meike Kliche (1); (1) Technical University of Munich, Freising, Germany
Analytical
Poster
Recent exploration of craft beer brewing focuses on the employment of
multiple hop varieties, while the variety of yeasts impacting beer
flavor is hardly exploited. Nevertheless, yeasts produce a wide range of
secondary metabolites, which influence the beverage’s final aroma
greatly. Ale-type beers are produced by employing Saccharomyces cerevisiae strains for fermentation at elevated temperatures, in comparison to S. pastorianus
strains, which produce lager-style beers at cooler temperatures. Still,
strain differences are expected to be prominent with respect to the
formation of volatile compounds, part of which define the flavor. The
differentiation and classification of new Saccharomyces isolates
is a time-consuming and laborious process of trial-and-error batch
brewing, which small- and medium-sized breweries do not have the
resources for. In this study a metabolomics approach was chosen to
characterize 11 yeast strains along the volatilomes produced under
fermentative conditions. The strains, eight of which are well known in
the brewing industry and represent a general flavor diversity, were
grown and preconditioned in YPD media and fermented under anaerobic
conditions at 9°C and 30°C for 5 days and 3 days, respectively. The
volatile profile was acquired via gas chromatography and mass
spectrometry (GC-MS) after concentrating the volatile organic compounds
in the headspace with an SPME fiber (PDMS/DVB). Fifty-four substances
were separated on a PEG column, with helium as the carrier gas, over a
temperature gradient from 60°C to 210°C. Two mutually exclusive sets of
seven and nine compounds were formed during fermentation with top- and
bottom-fermenting yeasts, respectively. For example, a strong
temperature dependency was observed for the formation of phenylethanol,
which is produced in a distinctly higher amount under the
“top-fermenting” conditions for all tested strains. Phenylethanol (as
sole compound) is associated with a floral odor reminiscent of rose.
Since a correlation of MALDI-TOF MS proteomic patterns with sensotypes
based on pilot brewing trials was demonstrated by Lauterbach et al.
(WBC, 2016), volatilome patterns are expected to correlate with
proteomic patterns as well. In our work, we demonstrate that
aroma-active compounds vary with strain and fermentation conditions and
can be identified in a simple GC-MS model. This approach, therefore, may
enable the fast screening of new yeast isolates for differences in
their flavor potential preceding the full brewing process. The “sorting”
of unknown yeast isolates into “volatilo types” suitable for specific
beer styles extends the potential for specialty craft beer brewing with
tempting flavors.
Meike Kliche received a B.S. degree in pure chemistry from the
Free University of Berlin in 2011 and an M.S. degree in toxicology from
the Charité, one of the largest teaching hospitals in Europe, in 2014.
She did internships in a laboratory for trace analysis in food and in a
working group researching primary cell culture assays as an alternative
to animal testing for contact allergenicity. Meike joined the Chair of
Technical Microbiology led by Rudi F. Vogel at the Technical University
of Munich in 2014, she is working as a doctoral student on the profiling
of Saccharomyces brewing yeasts using metabolomic and transcriptomic methods.
