Battle over the role of geology in wine typicity

According to Christopher Bargman (Geology and wine in South Africa, Geoscientist 15(4), April 2005), soil is the major influence on the growth of the vine plant. It provides: (i) a supply of water; (ii) anchorage in the ground; and (iii) a source of nutrition. According to education.mhusa.com, " soil is more than just dirt." It is, instead, "... a complex system of decomposed rocks that have been enriched over time by decomposed organic matter." The classic soil profile is shown below.

Source: westone.wa.gov.au

According to Wolf and Boyer (Vineyard Site Selection, Virginia Cooperative Extension), the best vineyard soils "permit deep and spreading root growth" and provide a moderate supply of water year-round. Mark Chien (Soil and Site Selection Considerations for Wine Grape Vineyards, Pennsylvania State University) posits that wine grapes do best in moderately fertile soils that are unsupportive of vigorous vine growth. What are the soil characteristics that will permit "deep and spreading root growth" and year-round access to water? Those characteristics are presented in descending order of importance in the table below.

But to many in the business of wine production and wine marketing, these "rudimentary" roles for soils do not tell the full story of its contribution to the finished product. According to champagne.fr (the website maintained by The Comité Champagne, the trade association that represents the interests of Champagne Growers and Houses):

The subsoil of Champagne is predominantly limestone. So too are the outcrops of sedimentary rock (75% limestone), composed of chalk, marl, and limestone proper. This type of subsoil provides good drainage and also imparts the particular mineral flavor found in certain Champagne wines.

The official Burgundy wine website (bourgogne-wines.com) stipulates:

In Bourgogne, Terroir is a broad concept which includes both natural and human factors. ... The basis of Terroir is above all the sub-soil and soil from which the vine draws its nutrients and which create a secret alchemy of colour, aromas and flavours.

In a Wine & Spirits article (Life in the Dirt: Claude and Lydia Bourguignon interviewed by Carson Demmond, www.wineandspirits.com), the subjects extolled the virtues of minerality, its relationship with the soil, and the capability of detecting it through mouthfeel. Lydia -- an Agri-Food Scientist and an Enologist -- characterized minerality as "... the perception of the rocks in the soil, by the palate." Further, "with a properly managed soil, the roots will dig deep into the subsoil, and it's the subsoil that determines the gôut de terroir. Without deep roots, all you taste is the grape variety and the cellar technology." Claude (an Agricultural Engineer with a Ph.D in Soil Microbiology) agrees that the minerality has to be based on tactile sensations because minerals are scent-free: "When you have ... different elements, the mouthfeel of the wine will be different. We can taste it and say 'this vine grows on clay' when we've never even seen the terrain.

Jennifer Huggett (Geology and Wine: A Review, Proceedings of the Geologists Association, 2006) and Alex Maltman (Role of Vineyard Geology in Wine Typicity, Journal of Wine Research 19 (1), 2008) are not as accepting of this central role of soils as is broadly presented. Maltman says that it has become de riguer when describing a vineyard to specify its geology and this, coupled with the geological indications common in tasting notes, has served to infer "... a direct link between the vineyard substrate and the resulting wine." According to Maltman:

Such perceptions bolster a valuable tactic for the wine trade, as, being one of the few aspects of wine production that cannot be translocated or easily replicated elsewhere, a vineyard's geology is something that can be invoked to promote a wine's typicity, to give it a marketable uniqueness.

Huggett uses two examples to knock back this idea of geology impacting wine quality/typicity. First she mentions the oft-noted "flinty" character of Chablis but wonders how such a material, being insoluble in normal groundwater, would contribute to the flavor of any wine. Further, she does not know what the flavor of something so hard and insoluble would be.

Her second push-back relates to Chablis and Kimmeridgian soil. Chablis is the "big island" in the Kimmeridgian chain and is home to some of the finest Chardonnay known. The defined region was recognized in 1923 by the Wine Tribunals as being grown on a sub-soil of Kimmeridgian limestone while wine grown anywhere else in Chablis would be classed Petit Chablis. The mid-slope in Chablis maps almost perfectly to the Kimmeridgian outcrop with the soft, carbonate-rich mud rock being capped by Portlandian Barrios limestone and supported by Calcares à Astarte, itself a limestone . This south-facing Kimmeridgian slope has significant sun exposure and is home to the Chablis Grand Cru vineyards (Wilson (Terroir) notes that geologic conditions identical to those experienced by the Grand Cru slope extend both northeast and southwest but that the vineyards on those sites are classed as Premiers Crus. That is an indication that Kimmeridgian soil is not the key ingredient in the making of a Grand Cru Chablis.). As a matter of fact, the reference to Kimmeridgian limestone in the definition of Chablis was discontinued in 1976, a tacit admission, according to Huggett, that "slope and orientation are of greater importance to wine quality in Chablis.

What do you think? Is soil a support mechanism or is it a key player in wine quality and typicity. I will explore the arguments of these two contrarians in upcoming posts.


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