Minerality and geology

Talking about MINERALITY

David Lefebvre is from a grain-farming family in the Meuse. After studying chemistry, he earned his oenologue’s diploma in 1994 and then worked as a winemaker in France (Domaine de Quattre in Cahors), in New Zealand and in California. After that, he spent three years as a consulting oenologist at the Consulting Laboratory Immelaté in Alsace. He currently works as an oenological journalist for a number of professional wine publications such as Viti and L'Est Agricole et Viticole. We have been following his articles on minerality with great interest.  We took the opportunity to sit down with him for a long discussion on the topic.

Interviewed by Jean-Marc Gatteron, text reviewed and corrected by David Lefebvre, translation courtsey of Peter Herman; this material was originally published in R&B n°100, Spring 2011

LeRouge & leBlanc: Your often cover minerality, a term that is very much used today ...

David Lefebvre: That's right. Minerality is coming into frequent use as a qualifier for wine. The term has been around for a long time, but its attributes are very variable, and it lacked a common definition, though there were regional ones. For decades, in Alsace, minerality meant the taste of oil. In Burgundy, it was characterized by sulfur odors, flint, gunpowder, and burnt, even oxidized aromas. In other regions, minerality is linked to pencil lead, graphite or ink. In fact, it can also be linked to very advanced brettanomyces (brett). You can see that the current usage is quite varied. There is no consensus on how to define it.


Your approach to minerality seems quite original ?

It stems from my background as a chemist. At university, the chemistry curriculum covers both mineral (inorganic)  and organic chemistry. The mineral part corresponds to 40% of the curriculum. However, when preparing an oenology diploma, the focus is primarily on the organic elements.  This is surprising, since we know that minerals are omnipresent in wine. In fact, wine is about 85% mineral, including water, which is a mineral compound, the CO2 and the various salts. In addition, there is the organic/ mineral interface with its organo-mineral elements. A mineral compound is stable over time. Wine is made up of these stable elements plus others which can still decompose. To illustrate my point about the lack of reference to minerals, we can look at the oenological “bible”, Ribéreau-Gayon’s, Handbook of Enology: The Chemistry of Wine Stabilization and Treatments. Of its 3000 pages, only 3 pages focus on minerals. I do not pretend to revolutionize oenology, but we need to agree on what ‘minerality’ means, especially since winemakers take it into account, but oenologists refuse to acknowledge it. I suggest that we approach this semantically: minerality is related to the minerals - though this approach seems to horrify wine merchants and sommeliers. By saying that minerality is related to the minerals, we mean it is related to the stable compounds of the wine on the thermodynamic level; those elements which are unchanging and unchangeable over time.


How do you define minerality?

I start from experiments. We need to target the tasting: we will concentrate on the impact of mineral compounds on the taste components of wine. There are two main effects. The first is salinity, and its different types. The most obvious is sodium chloride, but metallic tastes are also a form of salinity. There is thus a great diversity of salinities and it is their combined presence that brings this salty dimension. Magnesium, for example, has a distinctive salinity that comes close to bitterness. The second is the harmonization of taste components of the wine. The minerality interacts with these other components and modifies the tastes. For example, when one experiences sweetness in the presence of different saline solutions, this sweetness will be appreciated in different ways. The same type of interaction holds true for acids, alcohols, tannins and even for astringency.


So Minerality has no smell, only taste?

That’s it. Mineral compounds have no odor, but they can cause physico-chemical reactions such as CO2 production. The reason is simple: Mineral salts cannot turn into gas, they may be 100% soluble or insolubilized (they form crystals), but they don’t go into the air. In contrast, organic compounds do have an odor.


Then what causes the flinty odors ?

The causes are organic sulfur compounds. In addition to the four components of organic matter: carbon, hydrogen, oxygen and nitrogen (CHON), sulfur is also present


What about trace elements?

They are part of this minerality. In terms of Mendeleev’s table of the elements, if we exclude these four (CHON) components as well as excluding sulfur, all the other elements exist only in trace quantities in wine. The only way to measure minerals in wine is by dosing/analysing/extracting its ash. These can range between 2.2 g and 4 g of ash per liter. As an example, if we did this sort of measurement on mineral waters with different salinities, we would find that one might contain 2 g of ash and the other 4. The wine’s ashes, when assessed - the only reference measure in oenology to that lets us measure the wine's minerals - can range between 2.2 g and 4 g of ash per liter. And if we do a tasting of mineral waters, with different ash contents, they will have differing salinities. Obviously, wine tasting must take this minerality into account. For example, a wine may have 30g of residual sugar per liter; but this means nothing in absolute terms. It all depends on its mineral content. This is why we need a way to measure and compare minerality. I suggest that we construct this measurement by comparing the ratio of ash to dry extract. The ash is generated at a temperature of 700°C, and the dry extract by evaporation at 72°C.  In wine-making this ratio is in constant evolution as elevage, fermentation and aging all diminish the dry extract.


Could you be a bit more specific (about this index ?)

The mineral element of the ratio would be the weight of the ash minus the potassium, the latter being the most important mineral element (a spectrometer is used to perform the assay). Since potassium is not a vineyard parameter, but a wine-making parameter, its weight should be subtracted, as it can represent between a quarter and half of the minerals.  The potassium content can be modified during winemaking by varying the type of pressing.


How do minerality and acidity interact ?

Acids have a very special relationship with mineral salts. This concerns the phenomenon of salification, when the mineral salts harmonize the acids in the mouth. Conversely, acids have an enhancer effect on salinity. The salinity of a Riesling can be better appreciated because acidity is also present. When tasting with mineral water, minerals are seen to interact with alcohol. In the same manner, if a wine is considered too hot, it may not be too much alcohol, but too few minerals; this was the case with the 2003 vintages.


Are wines from limestone soils more mineral?

Not really. There is no obvious correlation between mineral presence and taste of a terroir. Even if a soil is limestone-rich, it does not mean that there will be more calcium in the wine. It is the same for a ferruginous soil. The parameters are too complex: there are processes at the root level, at the fermentation level (physical, biological, chemical), the filter of fermentations ... There is no easy conclusion.


So the more the wine is natural or biodynamic, the more mineral it will be?

To be able to answer this, you have to taste the wines while knowing their ash content. When we can get to that point, we’ll have a better idea what is going on.  Currently, my experiments are only with mineral water. There are too many variables present when wine tasting; with mineral water, there is only the water and the minerals, ex.it is easier to add alcohol and taste the results.


Does minerality correspond to the verticality of a wine?

Absolutely. It's the wine’s skeleton. In the same way, the wine’s horizontal aspect is its organic matter, its dry extract, its muscles. If a wine is over-developed, (body-built), enriched, boosted with gum arabic, we will find more dry extract. Currently gum arabic can be as high as 30 g per liter, which gives fat. Today’s tastes, unfortunately, prefer dry extract over minerality. It was one of Parker’s errors; he focused on the wine’s concentration ; thus on the dry extract. The concentration concerns both polyphenols and acidity. This tendency to ignore wine’s mineral dimension  (the chemical composition) always bothers me.


Do red wines have their own minerality?

Minerality has enormous effects on red wines especially on the harmony of the tannins. When these are too astringent there are two ways to make them harmonious:  either by fining or tannin-reduction, or by adding minerals. In our experiments with mineral water, we can clearly sense the taste difference between a tannin level in demineralized water and the same level of tannins in mineral water.  In the latter, the tannin will be harmonious while in fresh water it will be aggressive and astringent. Fortunately for wine, mineralistion through additives is just around the corner. The matter is far too complex; just think of all the elements in Mendeleev's table!


Are there different salinities?

If we profile the mineral composition of wines at the qualitative level (what makes them distinct from each other) there are as many salinities as terroirs. For example, calcium levels vary from 10 to 200 mg per liter.


That sounds like Burgundy climates?

In Burgundy, the expression of this minerality is detected thanks to the taste-vin . While the INAO glass is made to maximize the organic dimension of the wine in the mouth, the taste-vin tasting allows appreciation of its saline dimension. According to Jacky Rigaux, this science of the classification by terroirs is an Aristotelian approach. The Cistercians  (e.g.  Burgundy monasteries) sought to represent the terroir in wine. I have the impression that it was above all through its saline dimension. This raises the question of terroirs with characteristic aromas, but it is not contradictory (more complementary)  because there is always a organo-mineral interaction and minerals control organic bio-synthesis. The coenzymes resulting from these syntheses are minerals.  There's no contradiction. There may be an aromatic signature of the terroir, but it is also controlled by minerals (coenzymes, cupron-enzymes, all trace elements).


What do you mean by mineralization?

We’ll stay with the semantic point of view. Fermentation is one example of mineralization. During fermentation unstable compounds are transformed into more stable, more mineralized compounds.


So the more sulfur we add, the more we mineralize?

Sulfur freezes the process at a moment, but it prevents the completion (full realization ) of the biological mineralization. It leads to chemical mineralization by blocking decomposition of the molecules. The etching of colors is a typical example. When making an herbarium, sulfur is used to fix the color; the yellow will thus be preserved, but this process is a chemical mineralization. In wine,it is biological mineralization that is sought through fermentation, and all the art of the winegrower consists in controlling it. In all fermented products - from milk to cheese, from cabbage to sauerkraut, from grapes to wine - if we compare the taste of the fermented product with that of the product from which it is produced, the saline component appears. A fruit at the start is not salty, but the mineralization will reveal this saline dimension.

In the 17th century, the Cistercians were already discussing minerality (see Leon Potier de Gesvres,).  It is possible that we are rediscovering this subject today. In oenology, if winemakers viewed fermentation not just as the transformation of sugar into alcohol and carbon dioxide, but as the decomposition of organic matter, they would have a different approach to their viticulture and winemaking. This line of thought leads us to aim for mineral-rich grapes. When these are released by the mineralization, the saline components will appear.

 At the start, the minerals are bound up with the organic matrix, the calcium in the grapes is trapped with the calcium pectates. What happens to this calcium? There are enzymatic activities called pectolitics .  They reprocess the calcium and some is released in the wine; it is this free calcium that contributes to the salty taste. Another example of looking at fermentations through mineralization can be seen in wines under veil or champagnes. In this case, additional organic decomposition processes are added to the alcoholic fermentation, this results in a stronger mineral expression. Champagne's reputation is fully deserved, it has been won by incorporating supplementary fermentations that reinforce what was called “the spirit of wine”: its minerality .

An interesting avenue to explore would be a base wine with yeasts of veil, or more highly oxidized, which would then move on to become effervescent. I think that intuitively Anselme Selosse (the champagne winemaker) -  was working in this direction.