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Why Does Soil Matter So Much to Fine Wine?

Row of grape vines in California with mountains in the background, an embodiment of the Napa book experience

Why is Terroir so Important?

Terroir is a French term used to explain why agricultural products from certain areas and regions are different from other areas. It is now a commonly used wine term throughout the world to describe all the factors that go into growing grapes and making wine. Terroir explains why a Pinot Noir from Burgundy and California does not taste the same. The climate, terrain, soil, and geology, along with plenty of other factors give the wine its own, unique taste. Terroir is an important factor in viticulture and winemaking, as it significantly shapes the character of the wine.

But what exactly is terroir, and how far can this uniqueness be tasted in wine? The extent to which vineyard soils affect wine quality remains unanswered, and it is one of the most contentious issues in the wine world.

The Importance of Soil in Terroir

In Europe, it is widely accepted that the characteristics of vineyard soils, along with the influence of climate, are the most important factors influencing the quality of grapes and wine produced. The most important soil characteristics are generally thought to be those that are particularly important for the vine’s water supply.

Particularly good wines are frequently produced on soils that are highly permeable to water on the one hand but also constantly supply water to the vines on the other.

However, the water supply should not be so abundant that the vines grow excessively vegetatively. It is also necessary that the soil not be overly fertile or rich in mineral nutrients. In this case, the plant produces only small leaves, allowing the sun to illuminate the entire foliage as well as the grapes.

In this case, the elaborate foliage-clearing measures implemented during the summer are also scaled back. A sparse water supply also inhibits the growth of an overabundance of grapes in a beneficial way, because when a vine has too many grapes the quality of each can drop.

Wine Folly. 2017. SoilsDrawing. https://media.winefolly.com/soils-illustration-wine-folly.jpg. ‌

The Influence of Soil

The influence of soil on wine quality is not limited to the function of water supply, but also extends to other factors. The color of the soil is an important issue in viticulture. A bright floor reflects a great deal of sunlight while remaining relatively cool. Darker soils, on the other hand, absorb sunlight and convert it primarily into thermal energy; the darker the soil, the greater the energy yield. At night, the dark soils radiate energy like a heater, warming both the vines and the grapes.

Not only is the color of the soil important for its heat storage capacity, but so are its geological composition and moisture content. Because stone is much better at heat storage than sandy or simple soil, stony or stone-containing soils have a good ability to store heat and slowly release it again. Furthermore, stony soil is typically nutrient-poor and has excellent drainage.

Stone soils can hold little water, which encourages the plant to grow larger, deeper roots, which gives it more stability – the grapevine can drive its roots up to 15 meters into the soil. The ability to store heat is enhanced if there is moist soil beneath a stony layer. The rock absorbs heat quickly and conducts it deeper into the earth.

Grapevines growing in the sandy soils of McLaren Vale, Australia

Yangarra. n.d. Old Vines Grow in Sand at YangarraPhotograph. Accessed November 30, 2023. https://www.wineenthusiast.com/wp-content/uploads/2022/09/SOCIAL_Fallback_Yangarra_old_Vines_sand_Courtesy_Yangarra_1920x1280.jpg.

The Ideal Soils to Produce Fine Wines

The water in moist soil can store a lot of heat and release it slowly over time, protecting the soil from evaporation and the associated stronger cooling by the protective rock layer. These soils are frequently ideal to produce fine wines.

Simply moist soils, on the other hand, cool quickly and then warm up slowly, resulting in very slow heat absorption on the surface. On such soils, the vines frequently get wet and cold feet, which usually results in grape ripening problems.

Some of the most famous vineyard soils are densely interlaced with stones, as in the Spanish Ribera del Duero, or covered with stones, like much of Southern Rhône Valley, or even consist of pure gravel, as in the Medoc, Graves, Pomerol, and St. Emilion.

The rocky soils of Châteauneuf-du-Pape in Southern Rhône.

Chemical Composition

The variables regulating vineyard soils’ influence on vines and grape ripening only work optimally in soils with a normal, healthy chemical composition. A soil that is excessively acidic or too alkaline, or has an excess or lack of specific chemical compounds such as nitrogen, potassium, trace elements, and organic chemicals, can all have a negative impact on vine development, grape ripening, winemaking, and wine quality.

The interaction of these factors results in a wine’s independent personality and thus its character, which sets it apart from other wines. The more a grape variety is adapted to the soil and climatic conditions, the more clearly the typical character of a wine can be tasted.

Want to read more about wine? Try these books!

Land and Wine- The French TerroirVineyards, Rocks, and Soils- The Wine Lover's Guide to Geology

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