In the language of wine, the term terroir is often used as an all-encompassing framework, referring to geology, vineyard management, climate, grape varieties, viticultural practices, and winemaking techniques. It is a broad and complex concept, yet essential for anyone seeking to understand what makes a wine truly distinctive.
This article marks the beginning of a series focused on a topic as captivating as it is debated, focused on one of the terroir’s features: is there a direct correlation between soil composition and the sensory characteristics of wine?
A Useful Disclaimer
These contributions are not intended to be academic, nor do they aim to be exhaustive in examining the complex, and in some respects still poorly understood, relationship between soil type and wine.
My goal is more pragmatic: to determine whether, when the soil type is constant, there are recurring traits in the wine such as aromas, flavours and structural elements, that reflect the geological origin of the vineyard.
As the scientific literature has now amply demonstrated, there is no direct link between soil types and specific aromas or flavours. However, the soil does influence critical structural features of the grapes, such as acidity, tannin, and phenolic ripeness, which in turn shape the wine.
It must also be emphasised that climate, vineyard management, and winemaking techniques all play equally decisive roles in this equation.
Mineral Character: A Concept Worth Clarifying
In the last decades, the term minerality has been widely used, and arguably overused, to describe certain wines. It is worth attempting to clarify what this descriptor truly means in the context of wine tasting.
First and foremost, the so-called mineral character perceived in wine is not directly linked to the presence of minerals in the soil. That said, let’s explore what might cause those gustatory and olfactory sensations often associated with the idea of minerality (flint, chalk, graphite, gunpowder, or the feeling of wet stone).
Elements Contributing to Mineral Character
A key factor is acidity. Many wines described as “mineral” originate from cooler climates, where natural acidity in the grapes is higher. Furthermore, during alcoholic fermentation, succinic acid, a non-volatile acid, is formed. This compound can raise the wine’s total acidity and contribute to saline, savoury, and occasionally slightly bitter sensations.
Another element to consider is the presence of ions derived from the soil (sodium, potassium, calcium, ammonium, sulphate, carbonate, etc), which are found in the grape juice and ultimately in wine. These ions found in the grapes, are molecules capable of crossing plant cell membranes, may contribute, in combination with other compounds, to flavour sensations that tasters often describe as mineral.
Ion: any atom or group of atoms that bears one or more positive or negative electrical charge. Positively charged ions are called cations; negatively charged ions, anions. (Britannica)
Image by kp yamu Jayanath from Pixabay
Soil and Subsoil: A Distinction Worth Making
To better understand how soil affects the vine, it’s useful to distinguish two concepts that are often confused:
- Soil: the uppermost layer of earth, composed of sediments (sand, silt, gravel), organic matter, air, and water. It often includes multiple layers, each with its own texture and structure.
- Subsoil: the compact bedrock or parent material upon which the soil rests.
Key Soil Characteristics
Texture: determined by the proportion of clay, sand, and silt.
- Clay: fine particles, excellent at retaining water and nutrients.
- Sand: coarse, offers good drainage but poor retention of moisture and nutrients.
- Loam: intermediate texture often provides balanced growing conditions.
Structure: refers to how soil particles aggregate. It impacts water drainage, root development, and soil workability. Clay soils can become compact and impenetrable for roots, while sandy soils are loose and unstable, often requiring clay to gain compaction.
The soil’s ability to drain or retain water is the main characteristic that influences the growth of the vines and the ability to obtain a quality crop; this leads us to the concept of water stress. A mild water stress may lead the vine to produce smaller, more concentrated berries, with a greater skin to pulp ratio, which in red wines can be associated with better quality (higher levels of colour, tannins and aroma compounds). However, if water stress is not induced, this leads to large berries ideal for high-yield production.
How Vines Absorb Nutrients
Vines absorb water and essential mineral nutrients (such as nitrogen, potassium, magnesium, calcium, etc.) through their roots. However, organic nutrients are not directly available to the plant; they must be converted into inorganic, assimilable forms by soil-dwelling microorganisms and fungi.
Humus, the key organic component of soil, acts as a nutrient reservoir, but its effectiveness depends on the microbiological vitality of the soil. Invasive agricultural practices, such as the excessive use of herbicides or pesticides, can disrupt this equilibrium, destroying the microflora and reducing nutrient availability to the vine.
Essential Nutrients
- Nitrogen (N): Promotes vegetative growth, protein and chlorophyll formation.
- Phosphorus (P): Vital for photosynthesis and root development.
- Potassium (K): Regulates stomatal function and grape ripening; influences pH in the must.
- Magnesium (Mg): Core component of chlorophyll; aids in photosynthesis.
- Calcium (Ca): Strengthens plant cells; supports overall plant structure.
- Iron, Sulphur, Zinc, Copper, Boron, Manganese: Essential micronutrients required in small amounts. Imbalances can affect fruit quality significantly.
The soil’s pH (a measure of its acidity or alkalinity) dictates the availability of these nutrients; as different elements become more or less accessible at specific pH levels, this indirectly impacts the vine’s vigour and the grapes’ maturity.
Looking Ahead
In the upcoming articles in this series, I will explore different soil types and how they may influence the sensory profile of wines.
Using a comparative approach, I will taste and analyse wines from distinct geographical regions, made from different grape varieties, but all grown on similar soil types.
The focus will be on acidity, tannins, aroma, flavour, and structure, with the goal of identifying whether consistent traits emerge that can be linked to soil composition—independently of grape variety or the specific winemaking techniques employed by each producer.
Stay tuned—the journey into the heart of terroir has only just begun
Which wine do you feel best expresses minerality? Share your experiences in the comments below!
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Explore the connection between wine and the soil it comes from. In the “Wine & Soil” series, you’ll find in-depth analyses, tastings, and insights dedicated to different soil types and their sensory influence on wine style.