Wine is a marriage of sciences, from biology in the vineyard to chemistry in the cellar. What many consumers overlook is the importance of geology. While strolling through rows of grapevines, examining ripeness or leaf coverage, the very thing beneath our feet is one of the most essential factors in winemaking. Wine soil types range in texture, organic composition, pH, and drainage. Aspects of one particular type might be sought after in some regions and climates but not in others, making for unique attributes contributing to what ends up in our glass.
In this clip from Sommelier’s Notebook: An Intro to Soil, available on SOMM TV, Jonah Beer explains the importance of soil and its role in grape growing.
The different types of soil interplay around the globe, providing pockets that (depending on the climate) produce world-famous wines. It’s important to keep in mind that soil types aren’t universal across wine-growing regions. They’re not even exclusive to a specific vineyard. Soils are often a blend of different rocks, textures, and topsoils.
The following 10 soil types help hone a wine’s unique character and quality.
Best quality: retains water.
Clay soil works in an intricate lattice network that makes it difficult for water to retreat or drain. For this reason, deep clay subsoils retain their minerals and stay cool, which is ideal for hot growing climates. Wines made from clay soils are often opulent, robust, and bold.
Regions with clay soil: Right-Bank Bordeaux (Pomerol), Barossa Valley, and pockets of the Napa Valley between its alluvial fans.
Silt / Loess
Best quality: Retains water and heat and has high fertility.
With silt (or loess – a type of wind-born silt with high proportions of silica), its best qualities are equally threatening. Because it retains water well, it can sometimes result in waterlogged growing conditions that lead to disease. And due to its high levels of fertility, sometimes the vines don’t become vigorous enough for quality wine production.
However, silt soils mixed with a portion of limestone see the most success, particularly in cooler climate regions where the soil’s ability to retain heat comes into play.
Regions with silt/loess soil: Washington, Oregon, and Austria.
Best quality: well-draining and phylloxera free.
Sandy soils comprise tiny particulars of pulverized and weathered rocks. It drains well, delivering the most success in wet climates. For regions prone to drought, sandy soils are problematic. Because of its ability to drain well, diseases are rare. Another benefit is sand’s natural resistance to pests, like the louse phylloxera, making organic wine production easier to pursue.
Regions with sandy soil: Left-Bank Bordeaux (Graves and Médoc), Barolo (Cannubi and Serralunga d’Alba), and California (Lodi).
Best quality: Retains heat.
Gravel soils tend to produce full-bodied wines with more alcohol because of rock’s ability to retain heat. Depending on the region, stones can range in size, from pebbles to fist-sized Gobelet, like in Châteauneuf-du-Pape. Gravel soaks up the sun’s heat, releasing the warmth at night when temperatures dip. This ups the ripeness and resulting potential alcohol level.
Gravel has excellent drainage, but on the flip side, poor water retention. Meaning roots need to dig deep for nutrients.
Regions with gravel soil: Left-Bank Bordeaux (Graves and Sauternes), and the Rhône Valley (Châtaeuneuf-du-Pape).
Best quality: drains well but also holds water in dry weather. It has high pH making for age-worthy wines with high acidity.
When looking at the famous wine regions with limestone soil, it’s easy to deduce that it produces some of the finest wines on earth. Limestone is hard and firm, forming from decomposed fish bones and other organic material that once lived in the ancient seabed. The most common colored limestone is buff-gray (besides white chalk, a very soft and porous subset of limestone that allows vine roots to penetrate easily).
Regions with limestone soil: Burgundy, Champagne, Jerez, and Alsace (Zinnkoepflé).
Best quality: Retains heat well and has high minerality.
Schist is a metamorphic crystalline rock that forms over time and with pressure. It’s dense and made of layers of minerals, such as magnesium and potassium; however, it is poor in organic nutrients and nitrogens. It makes big, lush, and powerful wines.
Regions with schist soil: Spain (Douro Valley and Ribeira Sacra)
Best quality: Retains heat and warms quickly.
Slate is similar to schist in that it’s made from metamorphic, plate-like rock that compresses over time. However, it’s not as dense as schist. It’s dark, often with red, blue or black tinges, absorbing heat well and delivering it back to the vine to help ripen grapes.
Regions with slate soil: Mosel in Germany and Priorat in Spain. Priorat is known for its Llicorella soil, a mix of slate and quartz that dates to the Paleozoic era.
Best quality: creates deep-rooted vines with high acidity.
Granite is formed by the slow cooling of magma mixed with between 40-60% quartz. It has high pH levels, producing wines with high acidity and superb structure. The rock is also porous, providing excellent drainage and urges vines to root deeper for nutrients. This also makes them more resistant to extreme heat and drought.
Regions with granite soil: Beaujolais, Northern Rhône (Cornas), Spain (Rias Baixas), and Alsace (Brand).
Best quality: distinct minerality that (some say) translates into the wines.
There is no scientific link proving that the distinct minerality in Chablis, Sancerre, and even Champagne wines, are extracted from the compounds in the soil – but it’s certainly a compelling coincidence. Kimmeridgian soil combines limestone, clay, and fossilized shells from the late Jurassic age, between 152 and 157 million years ago. It has a gray color and was initially identified in Kimmeridge, England.
Regions with kimmeridgian soil: Chablis, Sancerre, Champagne, and the eastern Loire Valley.
Best quality: porous with good drainage.
Like granite, volcanic soils are porous, providing good drainage, urging vines to grow deep for nutrients. Volcanic soil results from one of two activities from long-ago volcanic eruptions. Vent-based soil is formed from pumice and tuff material ejected into the air and cools before settling onto the earth. Or lava-based soil results from the lava flow from the volcano. The soil is naturally rich in minerals like iron, calcium, magnesium, and potassium in both instances.
Regions with volcanic soil: Sicily (Mount Etna), Santorini, and Spain (Canary Islands).