Editorial

Wine Fermentation
Harald Claus
Institute of Molecular Physiology, Microbiology and Wine Research, Johannes Gutenberg-University of
Mainz, Becherweg 15, D-55099 Mainz, Germany; hclaus@uni-mainz.de; Tel.: +49-6131-3923542

Received: 2 February 2019; Accepted: 9 February 2019; Published: 12 February 2019

Keywords: extraction methods; color intensity; phenolic content; Saccharomyces; Lachancea; yeast
hybrids; metabolomics; sulfur compounds; oenological enzymes; process control

Currently wineries are facing new challenges due to actual market demands for creation of
products exhibiting more individual flavors. Serious climate changes have provoked a search for
grape varieties with specific features such as convenient maturation times, enhanced tolerances
towards dryness and osmotic stress as well as resistance against invasive plant-pathogenic
organisms. The next generation of yeast starter cultures should produce wines with an appealing
sensory profile and less alcohol. This Special Issue comprises actual studies addressing some
problems and solutions for environmental, technical and consumer challenges of winemaking today.
The contributions are focused on modern techniques and approaches at different stages of
fermentation.
The development of new sophisticated mass-spectroscopic methods has enabled considerable
progress in chemical analysis in recent years. It allows the identification of the major part of chemical
structures, at best the entire metabolite spectrum of an organism. Pinu [1] gives an overview of how
metabolome analyses enable the determination of the geographical origin of a grape or tracking of
yeast-specific characteristics. Analysis can also be limited to distinct substance classes and assists
elucidation of corresponding biosynthetic pathways.
One of these specific chemicals in wine are reduced sulfur compounds which usually produce
unpleasant off-odors and make such wines often unsaleable. Müller and Rauhut [2], outstanding
experts in this field, report on the origin and nature of such substances and the complex chemical
reactions that they undergo during wine storage.
Apart from gustatory pleasures and occasional stimulating effects, moderate wine consumption
has been recognized as beneficial to human health in many clinical studies. In particular, polyphenols
in red wine are associated with positive antioxidant and cardiovascular properties. Color intensity is
the first decisive quality feature for the consumer. Modern winemaking techniques take care to
maintain high levels of these desirable compounds. Sommer and Cohen [3] applied six different
physico-chemical treatments (e.g., ultrasound and microwave-assisted extraction) for effective and
sustainable color extraction from eleven red grape varieties. They concluded that color characteristics
of the finished product cannot easily be predicted from the initial extraction success but depend on
the specific anthocyanin spectrum of the individual cultivar used.
Moreover, the maturity status of the fruit can exert a significant influence on extraction efficiency
and color stability. Casassa et al. [4] showed that microwave treatment leads to increased phenol and
long-term color levels particularly in wines produced from unripe grapes and less in those derived
from ripe grapes.
Claus and Mojsov [5] summarize knowledge about current applications of technical enzymes in
winemaking. They stress that, although mostly obtained from mushrooms, many wine-associated
microorganisms produce enzymes of oenological interest. These biocatalysts could be used either as

Fermentation 2019, 5, 19; doi:10.3390/fermentation5010019 www.mdpi.com/journal/fermentation

enzyme formulations or directly in the form of starter cultures to increase juice yields, color intensity
and aroma of wine.
Saccharomyces cerevisiae is and certainly will remain the primary yeast for wine fermentations.
Nevertheless, König and Claus [6] report that non-conventional Saccharomyces species like
Saccharomyces bayanus, Saccharomyces kudriavzevii and their natural hybrids are of increasing interest
as they exhibit good fermentative capacities, producing wines with lower ethanol and higher glycerol
concentrations. In this way, the increased sugar content of the grapes due to global warming could
be counteracted. In addition, they may be tools to avoid stuck fermentations under nitrogen
limitations. Accordingly, Kelly et al. [7] demonstrated the potential of adapted autochthonous yeasts
such as strains of S. bayanus to produce individual wines even in cool climate regions.
Non-Saccharomyces yeasts, considered essentially “wild” spoiling microorganisms in the past,
are seen as beneficial today as they can improve the wine sensory profile, especially when grown in
controlled mixed starter fermentations together with S. cerevisiae. Vilela [8] reviews data about
Lachancea thermotolerans for wine production, which is characterized by reduced levels of alcohol and
volatile acids in favor of high concentrations of the flavor compound ethyl lactate. Thus, natural and
artificial Saccharomyces hybrids as well as collections of adapted wild isolates from various ecological
niches all over the world will further extend a winemaker’s toolkit, allowing specific fermentations.
Wine quality can be improved by post-harvest physico-chemical or biological measures, as
mentioned above, but of course also at the pre-harvest stage by appropriate winegrowing techniques.
One of these methods, the so-called cluster thinning, was evaluated by Mawdsley et al. [9] exemplarily
with a Pino Noir grape. Surprisingly, the authors found no quality increase in the phenolic profile
irrespective of the vegetation period (cold or warm).
An important factor of consistently high product quality is process control of wine
fermentations. Temperature plays a decisive role, which can vary significantly in different areas of
particularly large jacketed fermentation tanks and therefore is difficult to measure and to control.
Schmidt et al. [10] present an innovative open-source software program designed for the solution of
this basic problem.
Acknowledgments: The editor thanks all authors and the editorial staff who contributed to the success of this
Special Issue. On the occasion of his retirement, H.C. would also like to thank all members of the Institute for
Microbiology and Wine Research. Special thanks go to Martina Schlander for her years of invaluable technical
assistance and to Prof. Helmut König, who made him curious about the world of (wine) microbes.

Conflicts of Interest: The author declares no conflicts of interest.

References
1. Pinu, F.R. Grape and Wine Metabolomics to Develop New Insights Using Untargeted and Targeted
Approaches. Fermentation 2018, 4, 92; doi:10.3390/fermentation4040092
2. Müller, N.; Rauhut, D. Recent Developments on the Origin and Nature of Reductive Sulfurous Off-Odours
in Wine. Fermentation 2018, 4, 62; doi:10.3390/fermentation4030062
3. Sommer, S.; Cohen S.D. Comparison of Different Extraction Methods to Predict Anthocyanin
Concentration and Color Characteristics of Red Wines. Fermentation 2018, 4, 39;
doi:10.3390/fermentation4020039
4. Casassa, L.F.; Sari, S.E.; Bolcato, E.A.; Fanzone, M.L. Microwave-Assisted Extraction Applied to Merlot
Grapes with Contrasting Maturity Levels: Effects on Phenolic Chemistry and Wine Color. Fermentation
2019, 5, 15; doi:10.3390/fermentation5010015
5. Claus, H.; Mojsov, K. Enzymes for Wine Fermentation: Current and Perspective Applications. Fermentation
2018, 4, 52; doi:10.3390/fermentation4030052
6. König, H.; Claus, H. A Future Place for Saccharomyces Mixtures and Hybrids in Wine Making. Fermentation
2018, 4, 67; doi:10.3390/fermentation4030067
7. Kelly, J.; Yang, F.; Dowling, L.; Nurgel, C.; Beh, A.; Di Profio, F.;Pickering, G.; Inglis, D.L. Characterization
of Saccharomyces bayanus CN1 for Fermenting Partially Dehydrated Grapes Grown in Cool Climate
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8. Vilela, A. Lachancea thermotolerans, the Non-Saccharomyces Yeast that Reduces the Volatile Acidity of Wines.
Fermentation 2018, 4, 56; doi:10.3390/fermentation4030056
9. Mawdsley, P.F.W.; Dodson Peterson, J.C.; Casassa, L.F. Agronomical and Chemical Effects of the Timing
of Cluster Thinning on Pinot Noir (Clone 115) Grapes and Wines. Fermentation 2018, 4, 60;
doi:10.3390/fermentation4030060
10. Schmidt, D.; Freund, M.; Velten, K. End-User Software for Efficient Sensor Placement in Jacketed Wine
Tanks. Fermentation 2018, 4, 42; doi:10.3390/fermentation4020042

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