Bloomberg has announced that “Soil is more important than grapes when selecting a wine.” Alice Feiring, a wine writer, has also published a book that helps consumers choose their drink by “looking at its source: the soil in which it is grown”. There are restaurants that have wine lists organized not by grapes, wine styles, or countries of origin but according to vineyard geology.
Legend has it that Burgundian monks tested the soils in order to determine which one would produce the best wine. The vines are taking water and nutrients from the soil, so it makes sense that the ground is important for wine.
As I talk about in the new book, the enthusiasm to place geology at the forefront is new. Scientists discovered long ago that grapevines were not made of soil, but rather, in a sense, from sunlight, air, and water. Grapevines essentially use sunlight to remove carbon dioxide from air and combine it to water in the ground to create all the carbohydrate components that make up the vine. The grapes ripen and flavour precursors are produced. Fermentation converts these into hundreds of aromatic compounds, which determine the taste of wine.
The assertions above do not explain how a certain rock could affect the wine in your cup. Our current scientific understanding does not make it easy to understand how this could happen. These claims are mostly based on anecdotes; their scientific basis is thin.
Earthy tones. Ricardo Matias/Shutterstock
It doesn’t mean the ground isn’t important. The ground determines how the roots get water in a way that’s crucial to how grapes grow and ripen. The ground contains 14 essential elements for vine growth. In some cases, they may reach the wine in tiny amounts, but can’t be savoured. However, in other cases, they can affect our perception of flavours.
There are also other factors that can be overlooked. Consider the Fault Line Vineyard at Abacela in the Umpqua Valley in Oregon. The soil type varies dramatically over a small area, and the wine reflects these variations. In 2011, however, the owners began collecting data every 15 minutes from 23 sites for five years. The results revealed spatial variations in solar radiation intensity and temperatures during the ripening phase varied by almost 5degC within this vineyard. The soil was not the most important factor in determining grape ripening.
In recent years, there has been a lot of excitement among scientists about the potential importance of microbiology for the vineyard. This is because new technologies revealed different fungal and bacteria communities on different sites. It is not clear what effect this will have on wine taste, but the kingdom fungi contain organisms such as the Botrytis mould that causes the noble rot infection of sweet wines like Sauternes (which turns the grapes into raisins). There are also yeasts – those that control alcoholic fermentation, and others like Brettanomyces which can influence the taste. Because it is all very technical and invisible, most wine writings avoid such topics.
The soil in a vineyard is familiar, tangible and palpable. The truth is, most vineyards have been regularly fertilised, irrigated and gouged. Is this preoccupation with natural geology justified with all this artificial manipulation?
It is possible that we are missing some phenomena in science and will discover new ones as research continues. It doesn’t seem right to just make big claims without any basis, given our current scientific understanding of grapevine biology. It may sound impressive to say, for example, that an Austrian reisling wine is complex because it has slaty para gneiss soils, amphibolite, and mica. But, surely, there needs to be some explanation of how this works.
However, it is likely that these pronouncements will continue and maybe even expand. The idea that the wine in your glass is directly linked to a specific vineyard soil appeals to people, especially when it’s dressed up with fancy terms. It’s romantic, makes for good journalism and is great for marketing. Apparently, this is what trumps science.
