VFS Seminar January 30th, 2015
Factors causing sensory variation in Riesling wines from different terroirs, Professor Andrea Bauer
Terroir, the specific combination of a vineyard’s soil composition, mesoclimate and topography in interaction with the vines, has been widely acknowledged as an important factor in wine quality and style. Although geological diversity has been described for many vineyard sites, there is hardly any scientific knowledge about how the specific soil or climatic conditions translate into specific sensory properties of the wines grown on these sites and how much vintage or winemaking may further contribute to the sensory diversity.
To investigate the sensory impact of terroir, a range of 12 highly diverse vineyard sites were selected within the German wine growing region Pfalz, which were further enlarged one year later by 13 vineyard sites from four other regions. Riesling grapes were harvested from those sites in four vintages, which were either processed according to standardised winemaking protocol at a central location or according customary winemaking in the respective wine estate.
According to descriptive analysis wine originating from different vineyard sites yielded a considerable variation, although they were in close proximity. Applying discriminant analysis, it was possible to group the five bedrock types according to their sensory properties, and identify those aroma notes being typical for each bedrock type. Applying analysis of variance, the five bedrock types showed the most significant impact on sensory properties of the wines, followed by the comparison of standardised versus customary winemaking.
Applying PLS analysis to the sensory data and a data set combining soil and climatic parameters, 48% of the sensory variation could be explained by the soil/climate data set according to the first two dimensions. The highest coefficient of determination were obtained for the explanation of sourness related attributes (R2 0.82 – 0.94) explained by precipitation during the ripening period and gravel content of the soil. The odour of honeydew melon was related to the sum of growing degree days, calcium and clay content of the soil plant available water. A second PLS model could explain 49% of the sensory variation in the first two dimensions by using 49 aroma compounds. Here floral and apple attributes were highly correlated to a range of monoterpenes or ethyl esters, respectively.
The gained knowledge how site specific soil and climate parameters contribute to sensory difference in the wines will be an important contribution for the marketing of wine and communicating the concept of terroir to consumers.