Unlocking the Secrets of Terroir: How Does Soil Types Influence Wine Flavours?

You’ll have already seen us give plenty of column inches in previous blogs about countless factors that go towards the final flavours and profiles of our favourite wines. Whether that be grape variety, climate, or winemaking techniques, there is plenty that’s been said and plenty more to be said on all these diverse aspects. But one factor, in particular, deserves a closer look: SOIL

The soil is much more than just a patch of earth where the vine takes root. A closer inspection reveals it as a crucial component that directly affects how the vine grows, the grapes bud and ripen, and hence how the wine tastes and evolves. Indeed, different soil types have distinct properties that can impart unique qualities to the wines they produce.

What Role Does Soil Play?

The type of soil a vineyard is planted in can affect water retention, drainage, root penetration, temperature regulation, and the availability of nutrients, with each having a huge effect on the outcome of the grapes at harvest time.

For example, soil that retains water well can result in grapes with higher acidity, while soils that drain easily might stress the vine slightly, leading to more concentrated fruit flavours. From a grower’s perspective, mild hydric stress is actually the perfect condition for growing vines as it can achieve the optimal fruit concentration, which is highly desired.

Common Soil Types

There are several key types of soil found in vineyards around the world, each with unique properties that influence the local wines produced. Before you worry that this is becoming too much like A-level geography, here’s a closer look at some of the most prominent soil types and how they contribute to the wines you love.

Limestone and Chalk

Limestone and chalk soils are prevalent in some of the world’s most renowned wine regions, such as Burgundy, Champagne, and some parts of Rioja. The great thing about limestone and chalk is that they regulate water by holding moisture in dry periods and draining well during heavy rain. This balance is vital for the overall acidic, structure and flavour balance in the final wines, often exhibiting a sense of freshness, with bright acidity and mineral undertones.
Not all vines are well-suited to the alkaline nature of the soil, but those that are produce some of the world’s finest wines including the reds of the Cote De Nuits, Champagnes and English sparkling wines!

Clay

Clay soils are found in regions like Bordeaux and Barolo. Clay retains water and tends to stay cooler than other soil types. This ability to slow down the ripening process can maintain high levels of acidity whilst developing good structure and depth, with pronounced tannins and rich, concentrated fruit flavours.

In Bordeaux, for example, the clay soils in the Right Bank (where Merlot dominates) produce full-bodied wines with velvety tannins and dark fruit flavours in the famous villages of Pomerol and Saint-Emilion.

Gravel

Gravel soils are common in coastal or tidal river regions, like Bordeaux’s Left Bank areas of Pauillac and Graves. Gravel soils provide excellent drainage, forcing the vine roots to grow deep in search of water. This stress on the vine often leads to lower yields and more concentrated fruit flavours in the grapes.

Gravel also retains heat, which can help ripen grapes in cooler or more marginal climates. Wines from gravel soils often have a fuller body and structured tannins. In Bordeaux’s Left Bank, gravelly soils are crucial in producing powerful, age-worthy wines made primarily from Cabernet Sauvignon which loves to be planted on the gravel close to the Gironde estuary and Garonne river banks.

Volcanic Soil

Volcanic soils are increasingly thought to be capable of producing some of the most characterful wines in the world. Regions such as Italy’s Mount Etna, Santorini in Greece, and parts of Napa Valley, showcase well-drained volcanic soils rich in minerals, thought to contribute to wines with a distinct minerality, high acidity, and a savoury character.

Wines grown in volcanic soils often have a smoky or flinty character, with vibrant acidity and earthy flavours. For example, the white wines of Santorini, made from the Assyrtiko grapes, are known for their intense minerality, citrus flavours, and bracing acidity, all of which are attributed to the island’s volcanic soils.

Sand

Sandy soils can be found most famously in regions like parts of Australia’s Barossa Valley and California’s Central Coast. They tend to drain well and do not retain much water, forcing the vines to work harder to find nutrients, often resulting in lighter, more elegant wines with lower tannins. Sandy soils can also help protect against pests like phylloxera, which struggle to survive in such soils, meaning sandy soils are a playground for some of the oldest vines in the world.

Wines from sandy soils are often described as having more finesse and elegance, with delicate fruit and softer tannins.

Slate

Slate soils, synonymous with Germany’s Mosel region, are excellent at retaining heat, which is crucial for ripening grapes in cooler climates. The slate not only provides warmth to the vines but also contributes a distinctive mineral quality to the wines.

In the Mosel, Riesling grapes grown on slate soils produce wines with intense minerality, crisp acidity, and flavours of green apple, citrus, and sometimes a hint of petrol.

Soil and the Concept of Terroir

Given that this is a wine article, you know that we have a contractual obligation to mention the word terroir at least a few more times before signing off. But in all seriousness, “terroir” is so wonderfully defined and undefined at the same time, that any chance we have to have something concrete to say about it, we’re naturally going to jump at the chance.  Soil is most definitely a part of that concept.

Terroir, of course, refers to the combination of factors, including climate, topography, and human intervention, that influence the character of a wine. The interaction we’ve looked at between the soil and these other factors undoubtedly creates a unique environment that shapes wine in profound ways. For instance, a vineyard’s proximity to the ocean, its altitude, and the amount of sunlight it receives all interact with the soil to affect grape ripening and flavour development.

Given that the soil contributes so much to that sense of minerality, freshness, or complexity that sets the wine apart from others, we’d argue it’s right up there that soil is one of the most important factors in the production of fabulous wines.

This Blog post is written by Mike Turner
Freelance wine writer, presenter and judge

Mike is a regular contributor for The Buyer magazine and is a certified educator and ambassador for Bordeaux, Rioja, Ribera Del Duero, Barolo and Barbaresco, running trade and consumer events across the UK from his base in the East Midlands.