Untangling Terroir

a dirt row in a vineyard
Photo by Daniel Salgado on Unsplash

Terroir is one of the most widely used wine words, but it’s also probably the most ill-defined wine word. It’s a classic example of a French concept that doesn’t translate directly into English. Certainly, this leads to confusion, but I can tell you from experience that it is a poorly understood word even among French speakers.

The term terroir comes from the Latin word terra, meaning land or earth. In a sense, the word means “of the earth,” but in today’s vernacular, it has a more complex meaning. Whereas the vintage effect is the change in a wine’s quality and typicity from one year to the next based on weather, the terroir effect is the change in wine quality and typicity based on where the wine is grown.

Humans: A part of or apart from terroir?

a hand holding a bunch of grapes
Photo by Jodie Morgan on Unsplash

Terroir is defined in the Merriam-Webster Dictionary as “the combination of factors including soil, climate, and sunlight that gives wine grapes their distinctive character.” While this definition could include other factors, like human influence, its omission represents the major debate in the wine world. Are humans a part of or apart from terroir?

In my Introduction to Viticulture & Oenology class at the University of Bordeaux’s ISVV, I was taught that terroir can be considered from two angles. There is the agro-terroir angle, which is everything that concerns nature (i.e. hydrology, topography, soil type, etc.). Then there is the socio-terroir angle, which recognizes humans as an integral part of the quality of the wine. From this perspective, humans work to reveal the wine’s typicity, leading to high-quality wine.

As you can see, it’s impossible to separate human influence from terroir because there is no wine without human intervention. A Jura vin de paille wine has Jura terroir because humans put grapes outside to dry in the sun (a process known as passellirage), which increases their sugar content and leads to a wine with notes of dried apricot and peach. The typicity of Jura is because of the winemaking style in this region.

In other words, terroir is made up of the aspects of the natural world that grow the grapes AND the influence of humans both in the vineyard and the cellar. If it seems like terroir is a loaded word, it’s because it is. It means everything that influences the wine based on where and how the grapes are grown, from the climate to the soil to the way the vines are pruned.

What is “terroir wine”?

Most of the time, when we talk about terroir, we talk about the agro-terroir angle. We talk about how the soil and the climate influence the taste and smell of the wine. We talk about how limestone soils produce a terroir ideal for Pinot Noir. We even talk about certain wines being “terroir wines.” But aren’t all wines terroir wines?

Researcher Cornelius van Leeuwen from Bordeaux’s ISVV doesn’t think so. In his article, “The Concept of Terroir in Viticulture,” he makes a clear distinction between “terroir wines” and “branded wines.” He says that terroir wines are made from vineyards of a traceable origin, year after year. Their characteristics come from influences of climate and soil on vines. On the other hand, branded wines are produced at a larger scale, and the grapes cannot be traced back to the same vineyards year after year. Their characteristics come from influences of blending and “oenological processing” in the cellar.

How big is terroir?

Dr. van Leeuwen touches on an important issue in the conversation of terroir: scale. Is terroir regional? Certainly, Oregon winemaker Sam Parra from Parra Wine Co., who makes exclusively single-vineyard wines, would say no. He would say that the scale of terroir is at the level of the vineyard. That each vineyard has a different terroir.

But if we go over to J Vineyards & Winery in California, we find some single-vineyard wines and some wines that are blended from fruit all over the Russian River Valley. Their 2016 STRATA Pinot Noir is the latter, but they still sell this wine as a terroir wine. To J Vineyards & Winery, terroir is perhaps not only the single-vineyard scale, but on the regional scale or the appellation scale.

And the guys at Barefoot? The word terroir isn’t even mentioned once on their website.

Microbial terroir

Researchers from the University of California at Davis published a controversial article in 2013 that coined the term “microbial terroir.” Their work showed that there were regional distributions of grape microbiota in California’s Napa, Sonoma, and Central Coast growing regions. They suggest that regional differences in terroir may actually be explained by these regional microbiota distributions. In 2016, this same team found that they could actually correlate the vineyard microbiota with the chemical composition of the finished wines.

Not everyone is convinced. A review in 2017 highlighted the fact that the 2016 UC Davis study didn’t take into account the sensorial perception of the wines. So, while we can say that the chemical compositions of the wine are influenced by vineyard microbiota, if these microorganisms aren’t actually influencing the smells or tastes of the wine, can we say that they are a driver of terroir expression?

Terroir’s impact on wine aromas

This year, perhaps the most comprehensive article ever to be written on the topic of terroir’s impact on wine aromas was published by a big team of researchers from France, Texas, and Germany. Led by the terroir guru himself, Dr. van Leeuwen, this article summarizes the four main ways in which terroir acts on aromas: 1) air temperature, 2) solar radiation, 3) vine nitrogen status and 4) vine water status. This fourth point results from soil water holding capacity, evapotranspiration, and rainfall.

a diagram showing how air temperature, solar radiation, vine water status, and vine nitrogen status influence wine aromas
van Leeuwen et al. (2020)

As you can see, various factors of climate and soil are what drive the terroir effect. For example, air temperature and solar radiation, two climate influences, drive green and peppery flavors. The compound responsible for green pepper smells, IBMP, generally decreases as temperature and sunlight increase.

Soil nitrogen is also very important for the expression of volatile thiols in wine, the compounds responsible for grapefruit and passionfruit aromas in Sauvignon Blanc. When there is not sufficient nitrogen, these aromas decrease. The main reason is that nitrogen is necessary for the formation of glutathione, a precursor to volatile thiols. While glutathione itself is non-aromatic, during alcoholic fermentation, the yeast break the bond between the glutathione and the thiol, which reveals the thiol aroma. Thus, low nitrogen in the vineyard means less formation of volatile thiol precursors, and eventually, volatile thiols.

This article also suggests that by characterizing the four main drivers of terroir expression on a vineyard site (air temperature, solar radiation, vine nitrogen status, and vine water status), it is possible to predict aroma typicity from different terroirs. For example, since the literature shows a positive influence of solar radiation on dried fruit aromas, the general conclusion would be that vines that get a lot of sunshine will likely have higher dried fruit aromas. (Remember the vin de paille from Jura with dried apricot notes?)

Since terroir is one of the most used wine words out there, defining terroir and understanding how it impacts wine is one of the most important areas of research in wine today. The most important thing to remember is that place matters; where the grapes are grown undeniably changes the wine’s expression. And in a changing climate, understanding what factors influence terroir expression is paramount.

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