Rescuing minerality
Jamie Goode discusses the concept of minerality in wine, and its relationship to terroir

(This article is a written version of the talk I gave at the Wine & Culinary forum in Barcelona, October 2014)

In this article, I'd like to explore one of the most interesting and controversial topics in the world of wine, that of minerality. But before we get to discuss this topic directly, let's take a side step and look more broadly at the concept of terroir, which lies at the heart of the world of fine wine. There are four elements or definitions of terroir, each of which overlaps with the others.

The main definition of terroir can be summed up as the way the vineyard environment shapes the quality of the wine. Physical factors such as soil chemistry, aspect, drainage, average climate and slope have a strong influence on which varieties grow where and what the wines they produce taste like. Climate is obviously a huge factor, but the differences seen over short distances where there is a change in vineyard soil show that climate isn't everything. 

A second definition would be terroir as local flavour: the possession by a wine of a sense of place. This brings the human factor into play, as local traditional practices will influence wine flavour.

A third is summed up by the French term goût de terroir. This is the assertion that you can taste the terroir in the wine. Traditionally, this expression was used to describe rustic or earthy wines, and wasn't a term used for fine wines.

Finally, terroir can be used to refer to the physical vineyard site itself, independent of the wine, as in 'this is a good terroir', or 'the terroir is clay and limestone here.'

Terroir can operate at different scales. On the one hand we have the micro-scale: grapes harvested from different parts of the same vineyard can result in different wines even when the winemaking is the same. On the other, we have the macro-scale, with shared characteristics held in common by wines made from larger geographic regions (for example, 'this is a typical example of Central Otago Pinot Noir').

What about the human factor? Some definitions of terroir rule out human influence, but interventions – including viticultural and winemaking practices – may also confer a shared sense of place to wine.

It's possible that winegrowers could also be adapting their techniques to best exhibit regional differences in their wines. They may have in mind what a typical wine from a certain site is like, and seek to demonstrate this quality more clearly in the wine. They may have the character of a site in mind when they blend a single vineyard bottling, choosing to include lots of wine that exhibit its sense of place and blending away those that lack this personality.

This ‘typicity’, which is influenced by human factors as well as the physical characteristics of the vineyard site, helps maintain the sort of stylistic regional diversity that makes wine so interesting.

It is worth pointing out here that terroir can be fragile, and poor winemaking or picking grapes too late can interfere with terroir expression. Conversely, good winemaking and viticulture can maximize it.

So what are the mechanisms underlying terroir? Here we need to look at the biology of the grapevine. Plants are chemical factories. They use light, water, air, and trace elements to synthesize all they need.

Grapes—the starting place for wine production—are made entirely through the process of photosynthesis and subsequent plant biochemistry. Chemically speaking, the soil supplies water and dissolved mineral ions, which may or may not have any influence on the flavour of wine (we'll come back to this later). The plant makes everything else.

The current scientific consensus is that the way that soils have their influence on wine quality is through their effects on water availability. An ideal terroir gives vines enough to drink, but not too much, and – at the right time – gives the vine a bit of water stress. According to this view, soil chemistry is not important.

But the experience of many winegrowers testifies that soil chemistry actually matters quite a bit, and that soil effects are not just about water availability. Certainly, there's a lot of discussion in the wine world about soil type and its influence: more than you'd expect if soil chemistry were irrelevant. 

So this is where we need to look at soil chemistry, and in particular the mineral composition of soils. Plant science shows us that these could be having both a direct effect and also an indirect effect on wine flavour. The direct effect is through the minerals being taken up by the vine roots, ending up in the grapes, and thus ending up in the wine. It's not likely to be a strong effect, as most mineral ions have no smell and relatively little taste, but it could be having some effect. The indirect effect is through minerals (or their deficiency) altering plant gene expression, thus leading to differential production of flavour compounds or their precursors in the grapes. The chemical composition of grape must can also have an important effect on the way that yeasts and bacteria carry out fermentation, altering fermentation dynamics and causing microbes to produce different levels of flavour compounds.

The bulk of soil mineral content comes from decaying organic material, not decomposed rock, and it is microbial activity in the soil that affects the ability of soil to break down organic matter into mineral ions that can be used by the plant. This microbial activity is influenced by the availability of water, food, and oxygen. Soil texture is important: oxygen is more available in a loose uncompacted soil.

Various factors influence soil life, and as we examine them it soon becomes clear that farming grapevines involves compromises. There are things you absolutely need to do in the vineyard that might negatively affect soil microlife. You have to choose which compromises to make.

Fungicides, which are routinely used in viticulture, kill off not just fungi but also a high proportion of bacteria and actinomycetes. Herbicides and insecticides also kill off microbes and restrict the growth of others. But the worst culprit in terms of damaging soil life is copper sulfate (which is permitted as a fungicide in organic viticulture), which reduces microbial activity the most. But it simply isn't possible to grow vines without any chemical inputs.

So this is where we get to introduce the concept of minerality. It's a new tasting term: one that didn't exist until the 1980s, according to experts Steven Spurrier and Michel Bettane, who have been writing about wine for long enough to see this change. It has now become highly fashionable.

The literalist view of minerality is probably best summed up by soil scientist Lydia Bourguignon, who states that “minerality is the perception of the rocks in the soil, by the palate.”  Thus we have those who can detect chalk and flint in their Chablis, and those who find slate in their Mosel Riesling. But this literalist viewpoint isn't supported by science: the rocks don't dissolve and then get taken up by the vine. Besides, rocks don't taste of anything.

Jordi Ballester, a researcher from the Centre des Sciences du Gout in Dijon, in Burgundy, has studied the use of the term minerality by lexical analysis. He finds that it is a term being increasingly used, but without a clear definition. In his studies, he compared ratings of 34 wine experts and a trained panel, looking at the sorts of tastes and smells that people describe as “mineral.” What he found was that there were widespread differences among the tasters. However, some of the subgroups used the term in similar ways, suggesting that there is a cultural basis for its use.

So what are the different uses of 'mineral'? The first is minerality as an aroma. Wines that smell 'mineral' tend to be white wines, and the source of this matchstick/mineral character is most likely a volatile sulfur compound produced during fermentation by yeasts. The classic matchstick/struck flint character on the nose of some white Burgundies is really attractive, and it's now being deliberately sought by Chardonnay makers the world over. Volatile sulfur compounds are responsible for the wine fault known as 'reduction', and what we have here is a classic example of a compound that at one level is complexing, and another is a fault. The boundary between the two conditions is quite hard to pin down. 

The other two uses of the term involve minerality as a taste. The first, and least justifiable of these, is the minerality associated with high acidity in white wines. It's very easy to reach for 'mineral' as a descriptor when we come across bright, acidic whites, when really we should just say high acid. A related condition is when a wine tastes 'stony', again likely due to the acids. The second of these mineral tastes is, I think, the best use of the term, and it's a sort of salty minerality as you might find in some mineral waters, albeit usually at a low level. Here are some definitions of this sort of minerality:

“A wine marked by salty and mineral undertones balancing (and not hiding) the fruit, more often a white wine rich in calcium and magnesium as many mineral waters are.”

Michel Bettane

“It is the fraction on the palate that makes the wine taste more saline or salty. High acids or high tannins do not mean that the wine has lots of minerality. High salt contents make the acidity more ‘savoury’ and therefore less aggressive. Good minerality makes one salivate and want to have another sip or glass or bottle.”

Olivier Humbrecht

“For me, there are two forms of minerality that influence a wine’s qualities and characteristics. Firstly, the wine’s mineral content, which is about taste and texture when tasting a wine. It’s much like when drinking mineral water of a high mineral/salt content, there is a flavour/taste and an almost ‘osmotic’ experience, perhaps similar to drinking seawater, just much less concentrated and less salty.”

Gerd Stepp

Could this be caused my mineral salts in wine, absorbed by vine roots? The mineral content of wines fluctuates between 1.5 g/litre and 4 g/litre, which may be enough to confer some flavour on the wine. This would be very interesting indeed.

“It seems the soil’s exchange capacity of ions correlates with the mineral concentration of a wine,” says Stepp. “Also, a cold-stabilized wine has lower potassium content than the same wine unstabilized, and it tastes different and has less flavour, perhaps even less complexity.”

There is some evidence that soil type will influence the mineral composition of wine. In 2000, a plant researcher from Germany, Andreas Peuke, grew Riesling vines in pots containing three different soils from Franconian vineyards: loess, muschelkalk (seashell lime), and keuper. He collected sap from the vines and analyzed its chemical composition, and found differences among the different soil types.

In a more direct experiment, Randall Grahm famously put rocks into tanks of wine. “We were able to discern significant differences between the various types,” he reports. “There were major changes in the texture and mouthfeel of the wine, as well as dramatic differences in aromatics, length, and persistence of flavour.”

So this brings us back to soil biology. We discussed earlier about how important soil life is for making minerals available to plants. This could be why organic/biodynamic viticulture is often beneficial to wine quality, because it encourages the soil microlife to develop. Root exudates from plants are important in encouraging growth of soil microlife, and the vine is more likely to produce these if its nutritional needs aren't being easily met by fertilizer application. The vine age effect on wine quality may in part be to the expanded root system encouraging better soil microlife-vine interactions.

It follows that increased soil microlife could lead to more mineral wines. Finally, there's a question I'd like to throw out: is there a connection with minerality and ageability of the wine? I can't think of a scientific mechanism to explain this, but some wines that I'd describe as more mineral seem to age much better than their less mineral peers.

Have I succeeded in rescuing minerality? I'm not sure. But it is surely too soon to dismiss this concept, and I for one will carry on using the term in my tasting notes.

See also:

Visiting Central Otago, New Zealand (series)
Visiting Martinborough, New Zealand (series)

Wines tasted 01/11  
Find these wines with wine-searcher.com

Back to top