Terroir and soil – Minerality in wine

How does a vineyard’s soil affect wine? Can we legitimately talk about minerality in wine? Are the two concepts related? Part two of the terroir series

Minerality in wine? At first, this might seem a baffling thought. But minerality in wine can trigger some interesting discussions. Of particular interest to me is the relationship between wine and geology –  one of the main components of terroir.

This is the second part of my series dedicated to the fascinating topic of terroir. Here on Wine and Other Stories I will answer the question what is terroir? in three parts:

1. Part 1 : provides a general definition of terroir, along with a brief history of the term and its evolution
2. Part 2 (this article): focusses on the role of soil, a feature that is often considered paramount in defining terroir; this section will explain minerality in wine, what it means and how it affects your wine
3. Part 3 : deals with the role of human interaction. Is it part of terroir or something completely unrelated? Spoiler alert: opinions differ greatly on the subject!

Soil and minerality

In my previous article, I defined terroir as a combination of factors that determine the character of a wine and binds it inextricably to a certain place. These factors are: soil, topography, climate, local flora and fauna, grape variety / clone and human practices (the human element of terroir is highly controversial!). Out of the outlined factors, soil seems to be the one given the most weight (especially by French and other Old World writers). Soil and minerality in wine are intertwined concepts. In this article, I hope to shed some light on that relationship.

As soon as you start attending wine tastings or speaking with connoisseurs, you will inevitably find somebody who will talk along the following lines: “You can really taste the minerality in this wine, the limestone / marl / schist / slate / iron / chalk / volcanic (or others at your choice) soil is so evident!”

The bravest will go even further: “You can clearly taste the high content of chalk in the Kimmeridgian soil where the vines are grown!”

Wine tasting notes (even by professionals) echo this assumption. For example, writers use flavour descriptors such as iodine, oyster, seafood shell and chalk when referring to Champagne or other wine styles that express a clear “mineral” character.

Minerality: genesys and evolution

What is minerality in wine exactly? Today the term is very popular and is currently one of the wine world’s hottest buzzwords. However, minerality is a relatively recent term to describe a wine’s profile, first appearing in the late 1980s. 

There’s no unanimously accepted definition of minerality in wine. Some tasters attribute it to the nose of a wine. For them, minerality refers to a scent or – better yet – a scent cluster, since different “aromas” can be associated to minerality.

All mineral scents share certain characteristics: they are non-fruity, non-herbal primary flavours that to some extent bring to mind a kind of “stoniness”. Examples include:

• the chalkiness of Chablis or Champagne
• the smoky flintiness of some Loire sauvignon blanc (typically from Pouilly-Fume)
• the crushed slate scent of Mosel riesling
• the black stony accents of some Priorat
• the saline sensations of vermentino from Sardegna or assyrtiko from Greece.

However, other wine experts believe minerality is found on the palate and that it describes the particular texture of some wines. Soil scientist Lydia Bourguignon affirms that “minerality is the perception of the rocks in the soil, by the palate”. This definition seems to indicate that minerality is a taste akin to salitiness, and therefore perceived in the mouth. Italian wine jargon moves in that direction as well. When Italian sommeliers describe minerality, they talk about “sapidità” (sapidity), a term that is more commonly used for a taste as opposed to a scent.

From an organoleptic point of view, I think both stances are valid and non-exclusive. Minerality can refer both to scent and taste. Perhaps it’s more correct to talk about two different types of minerality: a minerality on the nose and a minerality on the palate.

Regardless of this distinction, a shared idea remains: you can perceive the influence of soil in the wine. But how?

When does soil matter?

As popular as they have become, the concepts of soil and minerality in wine only seem to be prescribed to certain wines. On a larger scale, it appears that soil (and terroir in general) is particularly relevant when the grape is slow ripening. This is true in cool climates, such as Burgundy, Champagne, Germany and moderate ones, like Bordeaux or Piemonte. Conversely, in warmer regions, the sheer ripeness of the fruit can obliterate all the nuances bestowed by terroir.

For some grape varieties, soil and the whole concept of terroir are very important. Such grape varieties include: pinot noir, chardonnay, nebbiolo and riesling. These grapes exhibit a chameleon-like feature. They are very sensitive to soil and climate variations. At their best, it’s said that these grapes “express their terroir”.

Impact of soil on wine

The underlying idea of minerality in wine is that you can perceive the characteristics of the soil in the wine. But what is the relationship between these two elements – soil and wine? It turns out it’s a complex affair, and to me, one of the most fascinating topics in the entire wine universe. 

Virtually everybody agrees that soil affects wine. The fights begin when we try to explain that interaction. There are two schools of thought on the matter:

• Direct effect: according to this theory, the minerals and chemical components in the soil are “sucked up” by the vines roots and contribute to the grape flavours – and ultimately to the wine style itself;
• Indirect effect: soil nature and composition affect other factors (water availability, heat, natural ecosystem) which in turn influence the wine

The first explanation appears the most attractive. Often it really does seem like wine tastes of minerals (even though stones do not have any smell on their own). It’s very common to smell chalk in Chablis and Champagne wines.  While rieslings from Mosel have a distinctive “tingling” sensation that we can only describe as slate minerality. 

The direct effect of soil composition on a wine’s nature has repeatedly proved untenable by geologists and several wine professionals. For example, Professor Alex Maltman from Aberystwyth University consistently dismisses the “direct effect” hypothesis. If you want a glimpse of his ideas listen to this interesting podcast from the Guild of Sommeliers.

In fact, researchers have proven the validity of the indirect relationship between geology, wine style and quality. This relationship involves certain characteristics of the soil. Texture, layering and chemical composition of a soil determine its water retention and heat regulation. These in turn affect how the vines produce fruit. 

For instance, numerous studies support that two soil characteristics consistently feature in top terroirs:

• The soil is infertile – but it is not deficient in minerals
• Water regulation is like clockwork: the perfect soil always gives just enough water to the vines, in every circumstance. For example in Medoc (Left Bank of Bordeaux) the lesser water holding capability of the soil is perfectly compensated by a sparse and deep root system, that is able to extract water at great depths. In the heavy clay-based soil of Pomerol (Right Bank of Bordeaux) the organic matter holds more water. This is crucial, as the only moisture available to the shallow vine root system is the water stored in Pomerol’s clay-based soil. The roots can’t penetrate any deeper due to the harder and more compact soil

Soil composition seems to also affect the vines’ vigour (the amount of vegetative growth in a plant). When it comes to vines, the best results are consistently achieved when both the leaves and berries receive a higher level of sun exposure. Further, there must be little shade, moderate vigour, restricted water supply, limited nitrogen and an appropriate training system.

Studies carried out in New Zealand showed a tight correlation between quality and vigour in wine. Again, according to these studies, the correlation between soil and wine is indirect. Soil naturally regulates a plant’s vigour, water and nitrogen availability, and these in turn affect the wine.

How much water do vines need?
It is not surprising that water availability and drainage appear to be of utmost importance in determining the quality of wine. Too much water means excessive vigour. Additional vegetative growth results in more leaves, green parts in the vine and less berries. This is detrimental for two reasons. Firstly, it means the vine uses more energy towards the green parts and less to its berries. Secondly, more vegetative growth culminates in a greater level of shadow for the berries resulting in them not ripening adequately.

Needless to say, water scarcity is also a problem. Drought is a major hazard for viticulture. The best soil is the one that provides the right amount of water in every circumstance. A bit of water stress is beneficial for the vines (especially after fruit set), since it allows for a greater concentration of flavour in the berries.

Soil chemical composition also influences the microbiotic ecosystem of the vineyard. Herbicides, pesticides and fungicides alter the chemical balance of the terroir, thus killing microlife and reducing its diversity. Such loss detracts from the overall flavour profile of the wine. Organic and biodynamic practices can be beneficial to the overall taste of the wine for this exact reason. These approaches are geared towards preserving the vineyard ecosystem. As a result, the vine is more likely to produce the microlife and nutrients not easily provided by fertiliser.

Complex interdependencies

To further complicate the topic (things are always complicated when it comes to wine… therefore be wary of oversimplifications!), the role of soil is highly interdependent with other factors that define a terroir. For example, the foot of a hill can be frost-prone and therefore not suitable for quality viticulture, whereas higher up the same hill you can plant vines and produce fine wine. In the two circumstances the soil is the same, but the mesoclimate is different.

From all the above considerations, a general principle emerges: terroir can only be fully understood if we simultaneously take into consideration several factors. Not just soil, but also climate, topography, vines and human practices (more on this in the next post).

Minerality and wine language

We have now seen how geology indirectly impacts a wine’s characteristics. Yet the most zealous wine writers still advise against using the word “minerality” (or its more specific declinations) to refer to a wine’s profile. According to these writers, such a practice encourages imprecision, implicitly supporting the myth that minerals are physically absorbed by vines and reflected in the wine. Nonetheless, it’s just a formal objection. As wine scientist Dr. Jamie Goode states in this wonderful interview about minerality in wine, we often use a “picture language” whose terminology must not be interpreted literally. 

Wine people have the peculiar task of translating scents and flavours into words – not an easy endeavour at all! Therefore we utilise analogies. Dr. Goode goes on to say that when we use descriptors like “leather” or “cherry” to describe a wine’s aromas, we don’t assume that the actual liquid contains such substances. It’s the same for “minerality”. We are well aware that the aromas don’t directly reflect the soil where the vines are grown. However, drawing similarities between scents and a shared vocabulary helps us to convey a wine’s profile.

Afterthoughts

I’ll end my article dedicated to minerality in wine with a curiosity. The vast majority of experts agree on the overall effect of terroir on wine quality (its regulation of water, mineral, heat and the vineyard ecosystem). What about the effect of terroir on wine style? Why does a wine taste the way it does in that particular terroir? Why does wine made with very similar winemaking techniques taste so different when originating from different terroir?

It comes as no surprise then that terroir is huge topic. My goal with this article is to spark some curiosity on the subject. Scientists, winemakers and wine experts have written loads on this subject and much more needs to be said. Science will never exhaust the romance and magic of wine.

I hope you enjoyed the second part of my series dedicated to terroir. Here’s a brief recap of the three articles dedicated to the topic:

1. Part 1 : provides a general definition of terroir, a brief history of the term and its evolution
2. Part 2 (this article): focusses on the role of soil, a defining factor in terroir, and its relationship with minerality in wine; what does it mean? How does it affect your wine?
3. Part 3 : the human factors contributing to the definition of terroir

For the next and final part, I will deal with the role of human interaction in wine terroir. Stay tuned!