GEOLOGY — Tour de France avec une différence (2)


Dan Bosence


February, 2005

The aim of my second trip with Nick Brookes was to assess the extent to which geology determines the quality of wines. Last year's effort took me through southern, western and central France so this year the wines and geology of eastern France demanded our attention. This trip took in the Tertiary—oops! Cenozoic graben of the Rhine, Saone and Rhone, all essentially running north-south with graben shoulders providing east facing slopes for vineyards. This is a significant geological control as Alsace and Burgundy are near the northern edge of vine growing in France and the early morning sun is important in warming up the late spring frosts that can damage the vine leaf buds.

Thomas 27
Domaine Thomas's vineyard terraces on the granite shoulder in Ammerschwihr

Well it was early morning sun that was needed in the first week of February as temperatures dropped to –4 degrees centigrade in the snow covered hills of Alsace; not everyone’s image of vine growing country.

Alsace produces a range of distinctive whites from grapes such as Riesling, Muscat, Pinot Blanc, Auxerrois, Sylvaner, Chasselas and Gewurtztraminer as single grape wines rather than blends. Vineyards are on the western shoulder of the Rhine graben where a series of faults downstep Palaeozoic granites, Triassic sands, marls, carbonates and evaporites and Jurassic limestones and marls. Rivers cut laterally through the rift shoulder and deposit large, east facing alluvial fans which together with the rift shoulder provide the best vine growing sites. The river terraces on the valley floor and north facing slopes are left for the lesser quality vin d’Alsace. Near Traenheim we experienced grand cru Riesling (crisp, dry, citrusy whites) from southeast facing crests and upper slopes on Keuper marls and dolomites whilst Gewurtztraminer (sweeter and concentrated fruits) grows best on the mid slope marls. Further south near Ammerschwihr vineyards of Pinot Blanc and Riesling are on a Weiss alluvial fan cutting through the graben shoulder and sourced from basement granite with well-drained sandy and pebbly soils. Gewurtztraminer grown on the granite we considered to have a distinctive sweet, rich apply flavour.

To the southeast, and just as cold, are the west facing scarps of the Jura Mountains which are reminiscent of our Cotswold scarps with Lower Jurassic marls passing up-section and up-slope to Middle Jurassic, shallow-water limestones. Here I was surprised to find vineyards in the lower, water-saturated, clayey soils of the Lias that contain fragments of ammonites and Gryphea. This challenges one of the commonly held beliefs (e.g. Pomerol, 1989) that vines can grow on any soil as long as it is well drained. Here we sampled a number of Chardonnay whites (the best with fruity flavours and a long finish); the vignerons believe that Chardonnay from the limestones are dryer and chalkier to taste whilst those from the marls are fuller, richer wines with more rounded flavours. For me to be convinced of this I would want to taste pure Chardonnays from vineyards on both limestone and marl of the same aspect and from vines of the same age and wines of the same years, to cut out some of the variables in this complex relationship between wine and geology.

St-Aubin's 1er cru vineyards sitting mid-slope in the distance
La Madone vineyard in Fleurie

Next to a more classic, and expensive, area of French wine the Cote d’Or; Meursault, Beaune and Gevrey-Chambertin. Possibly the most valuable limestone and marl scarp in the world and arguably producing some of France’s best wines. The Cote d’Or is a southeast facing scarp generated on the western border of the Saone graben. Making our way up through the vineyards took us firstly over marls and then up into limestones and some marl interbeds of the Middle Jurassic

The marls, together with hill wash, produce a poorly drained clayey soil and the Chardonnay grapes are used to make the unclassified Meursault and Beaune Villages. The premier cru sites are on the shoulder of this hillside where there are better drained soils on these Middle Jurassic bioclastic and oolitic limestones. Here a very thin pebbly soil (a few tens of centimetres) occurs between scattered limestone outcrops and supports Chardonnay vineyards of Charmes and Montrachet. The lithologies are very similar to those of the Middle Jurassic of the Cotswolds which, unfortunately for the growing band of British vine growers, faces northwest. Further North in Gevrey Chambertin the all important commercial boundary between land designated as Villages Gevrey and Premier Cru is a very slight break of slope. The 1:50,000 map proposes a river terrace for the slightly higher and more inclined and seriously valuable plot of land. So the quality of the wines and the fortunes of the vignerons are based on the geology and geomorphology, but for quite different geological reasons, along this one hillside.

South to Macon and Beaujolais where we tasted at vineyards in Fleurie and Villie-Morgon. Here the Gamay grape has been found to produce rich fruity, silky textured reds from a pink orthoclase-rich granite that weathers to produce thin, sandy, reddish/brown soils. The Fleurie appellation is defined by an outcrop of monzonite granite together with alluvial fans that drain off this granite on a very low relief shoulder to the Saone graben.

2 parcelle de Maison Rouge domaine Duclaux Domaine Duclaux's vines in the lieu-dit Maison Rouge, in Côte-Rotie's Côte Blonde

Into the Northern Rhone and a combination of tectonics, river power, and resistant Palaeozoic massifs generates the very steep east facing slopes of the Cote Rotie. True to its name (roasted hills) the sun at last makes an appearance and we have seen the last of the snow. These slopes are sometimes terraced but otherwise form up to 60 degree hillsides that are hand ploughed with the assistance of a winch to reduce weeds in the more organic vineyards. The rocks show a clear increase in metamorphic grade from north to south from quartz mica schists (Cote Brune) to gneisses (Cote Blonde) to migmatites and granites (Tupin). Not really my sort of geology but the Syrah grapes here produce low yield, high quality reds that are much sought after in the international market. Despite some serious tasting we were not able to detect significant differences in young wines from these different rock types. However the vignerons claim that some of the wines from the reddish brown iron-rich soils on the granites are drier to taste with an irony finish. The increase in iron levels is confirmed by soil analyses. These granites continue south on both sides of the Rhone and form part of the definition of the well-known wines of St Joseph and Crozes Hermitage appellations; Syrah based wines with rich blackberry and liquorice flavours.

Chateauneuf du Pape
The pebbly soil of Chateauneuf-du-Pape

Further into the sunny south we visited two vineyards in Chateauneuf du Pape. Here the geology is relatively complex, in fact it would make a rather good student mapping area for a number of reasons. It is set in the so-called Molasse Basin which is the Cenozoic foreland basin to the Alps, but it also has outcrops of older Mesozoic limestones that would have formed islands in Miocene times. Around these palaeo-islands siliciclastic and bioclastic sands were deposited along with some spectacular, dinner-plate-sized, oysters. These shallow-marine sands are overlain by a series of alluvial terraces formed by the Rhone as it eroded and transported pebbles boulders and sand from the newly formed Alps. The higher (older) terraces being made up of some distinctive rounded pebbles and boulders of limestone that form the soil, if you can call it that, of some of the Chateauneuf du Pape vineyards. This famous appellation is largely confined to the area of this upper terrace, but this is not a one to one relationship and very similar sites are apparently divided into Cotes du Rhone or Chateauneuf along boundaries decided on in the 1930’s on the basis of where the best wines are considered to be produced rather than an understanding of the difference between the Reis and Wurm river terraces.

To conclude my leg of this tour de France we visited a vineyard that was being developed and expanded on the Cotiere d’Azure. South facing slopes of Cretaceous limestone form the appellation of Bandol overlooking the Mediterranean. After a long period of selling grapes by the tonne to the local cooperative the younger members of the Suffrene family are now developing their own cuvees to the extent that new vineyards are being developed. This area has been excavated and around 600 tonnes of upper shoreface bioclastic grainstone with some superb Ophiomorpha traces are to be removed; hopefully to concentrate enough soil for the vines to root into and pass down the karstic porosity and fractures into the limestone.

This experience got me thinking on the plane back from Carcassonne about the uniqueness of wine production. I cannot think of any other industry that has been going on for around two thousand years that has such a long period between inception and product. Firstly, the preparation of the vineyard, planting the vines and then tending them throughout every year until they reach their potential at 30-40 years. Then the harvesting, fermentation and storage in barrels, and finally bottles, for perhaps 5-10 years for the wine to reach its best. Say 50 years from start to finish; a lifetime’s work and you pass your knowledge on to your family perhaps with a suggestion as to how it might be improved next time. This longtermism was brought home one evening as we were shown some ancient, gnarled vines that the 70+ year old vigneron said he could remember his grandfather planting. Vive la France I say!