Characterization of vineyard sites for quality wine production. German experiences

The quality of grapevines measured by yield and must density in the northern part of Europe conditons can be characterized as a type of “cool climate” – vary strongly from year to year and from one production site to another. One hundred year observations in Johannisberg from 1890 to 1991 demonstrate for the yield formation a clear dependancy from the year combined with a steady increase in productivity; latter a proof of positive clonal selection efforts. A similar and also pronounced time series is available for the must quality: Obviously are dramatic changes between the years. They happened during low yielding periods as well as in those with higher yields. The often forwarded claim that higher yields will depress must quality cannot be confirmed despite such long term observations.
Differences in must densities measured in °Oe ranging from 30 to 50 °Oe are not unusual. An explanation for this behaviour may be changes of weather conditions during critical phenological stages of the grapvines development (2,3,5). In a time series recording the stage of full bloom for “White Riesling” from 1947 to 1991 it can be demonstrated that the earliest onset of this stage is on julian day 159 and the latest on day 191, i.e. a span of one month. A similar course can be shown for the phenological stage “begin of ripening”: it is reached earliest at julian day 222 and latest at day 261, i.e. a range of more than one month.
These influences can be categorized as “macro climatic” influences. According to them the different grape growing areas can be differenciated, because the nothern viticultural areas differ stronger in must quality from year to year in comparison to the southem growing areas. The second scaling deals with spatial and time dependant variability in a growing region. Main factors depend on topography, soil type and climate.
The influences of both categories on must quality as well as on acidity will be described subsequently.