” A pedological approach to the classification of Burgundy crus “
Introduction
The Laboratoire d’Analyse Microbiologique des Sols (LAMS) has been working for over 10 years on vineyard soils, analyzing them on three levels: physical, chemical and biological. At present, the factors that explain terroirs are climate, topography, geology (Meriaux et al. 1981) and pedology (Moriat et al. 1981). This last criterion has often been considered secondary, and to date it seems that no scientific study has confirmed this classification of wines or supported the choice of grape varieties. The aim of this study is to clarify the possible role of topography and pedology on the classification of Burgundy crus and the color of the wines produced.
To do this, we measured the altitude of the plots and, on each soil, the total specific surface area of clays, per gram of dry soil on the surface horizon and on the bottom. The study we are presenting as a priority to the International Wine Academy is not yet completely finished, as it was carried out on data collected by L.A.M.S. before 2002, and since then new data have been accumulated. However, as the initial results are significant, we feel they deserve to be brought to the attention of academics.
Methods
Plots and classification
The measurements presented in this analysis have been carried out since 1991 by the Laboratoire d’Analyse Microbiologique des Sols (LAMS) on behalf of its customers, as part of its routine agricultural expertise. The measurements presented in this analysis have been carried out since 1991 by the Laboratoire d’Analyse Microbiologique des Sols (LAMS) on behalf of its customers, as part of its routine agricultural expertise. The classification chosen is the official classification of Grands Crus (INAO 1936), except for the parcel known as La Tache, which we have divided into La Tache Haut and La Tache Bas, as they were two different parcels until 1946.
This analysis covers 53 different plots:
Of the Burgundy vineyard parcels, 27 were planted with Chardonnay and produced white wine, and 26 were planted with Pinot Noir and produced red wine.
Measures
The total internal surface area of the clays was determined using the Methylene Blue method (Pham and Brindley, 1970.), which involves first determining the percentage of clays in the dry soil, then the internal surface area of the clays, in m2 per gram of clays.
Statistics
They were carried out by Florent de Vathaire, director of INSERM’s statistical unit. The analysis was carried out using classical parametric statistics and linear discriminant analysis methods, with SAS® software.
Results
They are summarized in the four attached graphs. In the linear discriminant analysis performed, the values for surface and bottom of internal clay surface and altitude predicted the classification of 46 of the 53 plots (graph N°1), 18/21 of the grand cru plots and 28/32 of the other plots, with all variables having a significant role. A linear combination of these three parameters also made it possible to classify the color of the grape variety planted on all (21/21) grand cru plots (graph N°3). For the other crus, the ranking was 25/32 (16/18 whites and 9/14 reds, graph N°2).
Conclusion
This analysis confirms that the classification of Burgundy crus and the tradition of grape variety selection, although established empirically, can be linked to scientific, pedological and topographical bases. Although these variables are not the only determinants of wine quality, and climate, farming practices and winemaking have an important and recognized role to play, our analysis shows for the first time that pedological parameters have a significant role, which has too often been considered secondary. The fact that the link between these variables and the choice of grape variety is clearer for the grands crus than for the other crus is probably explained by the fact that the choice of grape variety is better suited to the nature of the soils for the grands crus.
The relationship with altitude had been found empirically. Our analysis shows, however, that altitude is not enough, and that soil parameters must be taken into account when choosing which grape variety to plant on a plot, as they have their own role to play in the quality of the wines produced. Graph 4, which we present for Bordeaux wines, shows that the criterion we use is also discriminating for this region. The current data we have on this region are still insufficient to draw any conclusions on the subject, but they already show a strong tendency towards the validity of our classification index, for both vintages and color.
The initial results we have the honour of presenting to the Académie Internationale du Vin confirm, through science, the validity of the classifications made by tasting. We hope to be able to extend our data to other wine-growing regions in France, Europe and the New World, to help understand the role of soil in the expression of terroir in wines. This index can also be used as a decision-making aid when planting new vineyards.