Wine with a deep flavour

The Winemaker's Dance: Exploring Terroir in the Napa Valley

University of California Press. 2004. 243 pp. $35.95, £22.95 0520235134 | ISBN: 0-520-23513-4
I'm getting something earthy: differences in bedrock can affect both soil colour and a wine's flavour.

The taste of a wine depends on more than just the variety of the grape from which it is made. Winemakers and wine connoisseurs are concerned with terroir (pronounced ‘tair-wahr’), which refers to everything else that controls the flavour of wine: climate, subsoil and even the manipulations done in the winery.

Many winemakers believe that the taste of wine comes from the soil that supports the vines. But the soil is only about a metre thick, whereas the roots of the vines extend down about 10 metres or more. The soil is in equilibrium with the local climate: its clay and organic components smooth out the delivery of water to the plants, and cation-exchange processes supply major nutrients. But the minor compounds that control the taste come from the much more voluminous subsoil. The bedrock slowly weathers under the action of water, carbon dioxide and organic acids. This process delivers a continuous flux of subsoil-dependent compounds to the vines, and is a key component of the local terroir. In The Winemaker's Dance, geologists Jonathan Swinchatt and David Howell evaluate every aspect of the terroir of a small but well known winemaking region and place their findings in a global context.

The Napa Valley, northeast of San Francisco, is in many ways similar to the famous Bordeaux region of France. They are at similar latitudes on the west coasts of continents, and principally grow the warm-climate grape variety Cabernet Sauvignon. They are both about 50 kilometres from their respective oceans, and large estuaries — San Francisco Bay at Napa and the Gironde at Bordeaux — provide the cool night-time temperatures that preserve the acidity of their premium wines.

The most expensive Napa Valley wines grow on alluvial fans (known locally as ‘benches’), which are piles of gravel and interbedded silt that have streamed down off the flanking mountains. At Bordeaux, the counterparts to Napa's alluvial fans are the graves (gravel mounds, again interbedded with silt) formed by streams during ice-age low stands of the estuary.

In an effort to link the taste of wine to the subsoil geology, the authors studied Diamond Creek Vineyards, where the vines are planted on upland slopes at the north end of Napa Valley. The 8-hectare property is cut through by a network of faults that juxtaposes three dissimilar geologic blocks. During vineyard development, the owner recognized three strongly contrasting soil colours, and used them to divide the property into three vineyards. These were planted in 1968 with Cabernet Sauvignon cuttings from two first-growth vineyards at Bordeaux.

Throughout its history, Diamond Creek has had three vineyard-designated bottlings. Similar winemaking practices are used for each but the wines consistently taste different. Wine from Red Rock Terrace (which has a basaltic lava subsoil) has velvety tannins with rich cherry and blackcurrant flavours; that from Volcanic Hill (volcanic-ash-bearing sandstone) has tannins that are youthfully firm but long-lived with berry and smoky flavours; and wine from Gravelly Meadow (pebbly stream sediment) has firm tannins with herb, blackberry and earthy flavours.

Two major factors affect the subtleties of wine taste. The first is the ‘character’ of the wine — the grape variety plus all the elements of its terroir — and the second is the physiology of the people doing the tasting. Tastes vary: one person's crème de la crème is another person's plonk

To investigate the effect of local terroir on the palettes of ordinary consumers, Swinchatt and Howell conducted a blind tasting in 2002, serving eight premium Napa Valley wines with a meal. Most participants ranked the wines differently when they first tasted them to when they tried them again with a meal. When asked which of the eight they preferred overall, the votes were spread quite evenly. In an extreme case of differential preference, one person found the aroma of one wine to be particularly offensive, whereas another said of it: “I'd like to have a bowl of that beside my bed, just to smell.”

This variation in personal preference is in marked contrast to the ‘expert’ opinion of wine-ranking services, which tend to favour blockbuster wines that are extremely intense, particularly on first tasting. This has led to winemakers letting their grapes hang as long as possible on the vines, and extending the time that the wines macerate on the grape skins. Swinchatt and Howell deplore the homogenization that this is causing to the taste of the world's wines. They recommend that consumers ignore the wine-ranking services, seek out diversity, and savour it.

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Moore, G. Wine with a deep flavour. Nature 434, 438 (2005).

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