How Soil Types Affect the Wines We Drink

Rutherford dust, the minerality of Chablis…just two of the many ways wine geeks will describe wine in relationship to the region, or soils that they are grown. While many factors contribute to how a wine tastes, soil does contribute to characteristics in wines, as well as the vines’ ability to grow. And while terroir is often used to describe a wine for its “sense of place” — meaning the regional microclimates and grape varieties grown — when it comes to soil, we’ll need to dig a little deeper (pun intended) to discover why it really matters.

How Different Soils Are Formed

There have been a lot of research studies done over the years in regards to the different soils of wine growing regions. A lot of professors and other experts may argue back and forth on how exactly soil does affect a wine’s taste. But first let’s take a step back and look as how Earth’s formation and evolution has impacted the wines we drink, how we went from star dust to a nice glass of Barolo. But don’t worry, you’re not going to need a geology degree to understand this.

As the earth was formed and changed over the years, many historical events have lent some great influences to the wines we drink. Most of us understand that as the earth plates moved around, what once was an area under water, might now be above. It was this moving of the tectonic plates that altered the crust, pushing up some regions, and down in others. And these layers of different soil types were pretty much just along for the ride.

Kimmeridgian Soil

Champagne, Burgundy, and even the Loire Valley of France sit on a type of soil known as Kimmeridgian; a combination of limestone, clay and fossilized oyster shells. Fortunately, a friend of mine visited Domaine William Fèvre a few years ago and sent me a piece of rock from their vineyards. But for those of you without a piece of Chablis sitting on your bookshelf, you can read more about this very unique soil type here. While there is no scientific evidence that proves that grapevines can extract chemical compounds directly from the soils, they do give the wines of Chablis, Sancerre and even Champagne a distinct minerality that is unique to wines of these regions.

Volcanic Influences

But not all soil types were due to the moving around of earth tectonic plates — some were a result of the eruption of volcanoes.

You’ve heard of Mt. Vesuvius, right? That still active volcano that erupted not once, not twice, but several times, wiping out the Roman settlements of Pompeii and Herculaneum? Well, what goes up, must come down! And when the dust settled, rocks, ash and molten lava became forever a part of the region’s soils. Today, Vesuvio is its own region with vineyards on the slopes of this active volcano. Again, while many scientists say that wines can’t take on flavors of their soils, the soil types in this area really does allow certain types of grape varietals to flourish with smoky, mineral flavors.

Galets

Another example of Mother Nature’s influence on wine can be found in the Châteauneuf-du-Pape region of the Rhone Valley in France. After the last Ice Age, floodwaters poured through the valley depositing rocks and forming the oval shaped stones, or galets, that are seen in many of the region’s vineyards. These round stones retain the suns heat during the day, allow proper drainage for the vines, while also acting somewhat as a barrier to the other soil types below. Think of the galets as a solar powered heating blanket, keeping the grapevines warm and cozy at night. Large stones like these are also found in the Rueda region of Spain; helping by creating proper drainage at the upper levels of the various soil types, and protecting the more water-retaining soils below them. The structure and size of soil is a study known as granulometry, and scientists in this field study how certain crops will grow in various soils.

The Châteauneuf-du-Pape region does have other soil types as well under those layers of rocks. Some, like the prestigious Chateau Rayas lack these galets completely, and have a more traditional looking vineyard. This is a prime example of how the soil’s physical attributes can affect how grape wines grow, and even affect the quality of the wine.

Soil Profiling

Soil profiling is another study done on vineyards around the world. This is a study where researchers take a look at not just the top layers, but all those that lay underneath and even the way they were created as the earth we know today was formed. Grapevine roots can grow up to fifteen feet deep, so those layers down below can alter a wine as the vines tap into those various soils, each type affecting how the vine grows and ultimately affecting the grape’s flavor. This is what is often believed to be responsible for the complexity of a wine coming from grapes of very old vines.

This is where we get into the chemical and biological elements of soil. Without getting too technical, soil is made up of a variety of compounds. These compounds contain nutrients that the grapevine needs to grow. But grapevines do best in soils that are not super rich in nutrients, but rather lack certain ones and are balanced.

Nitrogen is important to grapevines as they use it to grow and reproduce. But in excess it can have negative consequences resulting in vegetal aromas like green beans. Potassium deficiencies in a soil can lead to issues where the fruit might fail to ripen properly. High salinity in a soil can also have negative effects as well. The pH levels of a soil is another important element that affect the vines ability to absorb the nutrients it needs. You’ll see pH levels talked about a lot when it comes to wine. It’s used by winemakers to also determine ripeness in relation to the acidity. Vines lower in pH tend to produce more crisp wines, while those higher in pH are more susceptible to bacterial growth.

Identifying Soil Types

Of the many various soils, there are four primary types used in viticulture: sandy, clay based, silt and loam.

• Sandy Soil Types

  Sandy soils produce elegant wines that are usually low in tannins and higher in aromatics. Take for example the Cabernet Sauvignons grown in the more sandy soils of the Graves region in Bordeaux. The red wines here are much lighter in style than their counterparts of the wines from the more northern Medoc region. Sandy soils have historically also been known to be resistant to Phylloxera.

• Clay Soil Types

  Clay soils, like those of the Ribera del Duero in Spain help produce bold wines. The clay soils help the vines stay cooler in these warmer growing regions.

• Silt Soil Types

  Silt based soils, like those found in Washington (which is also an area formed by the after effects of the Ice Age) are known for helping create rounder style wines that are slightly less acidic.

• Loam Soil Types

  Loam soils, like those found in Napa and Sonoma Valley, are a mix of the above with added organic matter. Other soil types that are combinations include: alluvial, sandstone and shale, each offering their own uniqueness to the wines from vines grown in them.

So, like us humans, grapevines need food and water to live — as well as the sun, of course. Soils help regulate climate fluctuations, retain heat, and can even help in dispersing water. Depth and composition of a soil, nutrients, drainage and water retention, pH…all have their effects on the wines we drink. If it weren’t for these soils and their fine balance of all these elements, we wouldn’t be drinking the incredible wines that we do.