Significance of factors making Riesling an iconic grape variety
After completion of a winemaking apprenticeship Ulrich Fischer graduated with a B.Sc. degree in viticulture and oenology from Geisenheim, Germany and with a M.Sc. in food science at the University of California, Davis, USA. After obtaining a PhD in chemistry at the University of Hannover, Germany he started in 1995 at the DLR Rheinpfalz in Neustadt. Since 2003 Ulrich Fischer is head of the Institute for Viticulture & Oenology and honorary professor at the Technical University of Kaiserslautern. In 2010 he acted as founding director of the dual B.Sc. Viticulture & Oenology program at the Weincampus Neustadt where he lectures oenology, wine chemistry and sensory courses. His research focuses on the formation of flavor compounds in the grape, their utilization and further modification during winemaking as well as their sensory relevance. Fischer is member of the scientific advisory board of the Food Industry Research Council and serves on the management board of the International Mundus Vini wine competition.
Riesling is the iconic grape variety of Germany and accounts for 23% of the German viticulture acreage, which comprises 45% of the worldwide Riesling plantings. Riesling wines offer a wide array of styles from crisp sparkling wines to highly concentrated and sweet Trockenbeerenauslese or Icewines. However, its thin berry skin makes Riesling more vulnerable to detrimental environmental threats than other white wine varieties.
Trying to adapt Riesling to climate change we investigate how to mitigate premature Botrytis infections, the loss of quality and yield due to sunburn or increasing levels of TDN, which causes the unique petrol off-flavor. Weather variation from year to year necessitates an active acidity management, either diminishing acidity by skin maceration or use of lactic acid bacteria but also more recently lowering pH by ion exchange resins or malic acid producing yeast. A strong focus is to enhance intensity and diversity of Riesling aroma by viticultural and oenological measures, which are controlled by sophisticated chemical analysis including a measure of odorless precursors.
Riesling is a highly transparent variety in respect to terroir, deviating strongly in odor and taste due to different bed rocks and soil types, micro climates and inclination of individual vineyards. Applying comprehensive stable isotope dilution analysis of volatiles and sensory evaluation we could demonstrate not only the sensory relevance of terroir, but also how stable these patterns were over five vintages and even individual winemaking measures. Using next generation gen- sequencing techniques to study spontaneous fermentations, we could also reveal the significant impact of site specific microbiomes.
Riesling wines are highly acclaimed for their longevity due to their exciting balance of acidity and sweetness. Re-tasting terroir defined Riesling wines again after four years revealed the expected modification in sensory terms due to aging, but prove that the general differences among the specific terroir expressions were conserved through the maturation process.
Many of these scientific puzzle pieces were successfully implemented by the Riesling producers over the last two decades and they succeeded to improve Riesling wines in each of its multitude of stylistic facets. However, it will be a challenge to preserve their unique and diverse characters in the course of progressive climate change.