MINERALITY: Animal, Vegetable or Mineral?

The term ‘mineral’ is a fashionable wine characteristic right now, but what does it actually mean? Sally Easton MW finds there is a lack of precision and unanimity in defining the term and suggests it be used only very cautiously.

The term minerality is bandied around with gay abandon by winemakers and industry folk alike, who regularly struggle to define it precisely when probed. But, “Minerality in wine is difficult to define,” says Kees van Leeuwen, professor of viticulture at ENITA – Bordeaux University, precisely “because it does not refer to a specific substance present in wine.”

This leaves us floundering with an imprecise language to describe the term. Among many, Andrew Jefford has described it as an “absence of fruit, animal, wood”. Others intone the chalky, flinty paradigm. So if it’s not animal, nor fruit nor vegetable, must it be mineral?

In trying to unravel minerality, we have to overcome “tasting by association”, which is trained into our understandings.  Professor Ulrich Fischer, at the department of viticulture and oenology at Neustadt in Germany said minerality is a “self-fulfilling prophecy – you learn Chablis is flinty; Mosel is wet slate. You know you have heritage and you pick it up”.  But if you lick that flint or that piece of Mosel slate, there’s not a lot of direct flavour.

One thing’s for sure: it’s trendy. And there’s an implied quality innuendo when minerality is mentioned. So there is a responsibility not to abuse the term. For analytical study, certain chemical compounds are attributed to certain aromas, for example the floral character of monoterpenes or the green pepper of methoxypyrazines. The chemical compound can be analysed to study how the character is formed. Yet no one compound has yet been attributed to mineral character, which explains why there is no consensus on its use.

Sensory analysis

We move from analytical study to sensory study, where studies of Sauvignon Blanc by Dr Wendy Parr, sensory scientist at Lincoln University in New Zealand, using experienced wine tasters and winemakers from both NZ and France, has identified “an aroma and flavour characteristic that they term ‘flinty’, ‘smoky’ (but not smoke ‘smoky’), or ‘minerality’”. She adds: “French people also use the word ‘silex’ to describe this note.”

In an ongoing study of the terroir of Riesling in the Mosel, Nahe, Rheinhessen and Pfalz, Fischer and his team “do descriptive analysis, evaluating wines on the intensity of 10 aromas, such as citrus, pineapple and floral, and taste. People can perceive the smell of mineral wine.  In order to be scientific we have to produce a standard, which is reproducible, so we took small stones, wet them, and we looked for a smell which is reminiscent of wet slate, wet pebbles. For the taste we couldn’t yet find a standard, however”.

“The standard for minerality is wet pebbles, wet quartzite,” Fischer adds, “and above all it is a smell. Also think about iodine smell at sea and maybe think about fresh oysters. Ozone is maybe coming close, it fits into the concept. “

The terroir connection

You can have terroir without minerality, but can you have minerality without terroir expression? Fischer thinks not, saying: “Minerality is appreciated by people because it relates to the character of the soil. Since the turn of the century, we’re wanting wines with more individuality. One way is to look for more specific terroir wines; another is to use more spontaneous fermentation. This is why wines are getting more mineral. Many wines are fermented warmer [above 18°C]. The fermentation esters are reduced, and other properties of wine are getting stronger, and one of these seems to be the mineral character.”

Parr concurs: “From our data, it is related to the wines from specific areas. All the wines in our studies are tasted blind in opaque glasses and yet the wines from Loire and Saint Bris, near Chablis, always show up with higher intensity ratings to the flinty notes.“
Another area that scientists so far agree on is that the root route does not exist, in that minerals taken into the plant are not replicated in the form or proportions that they are represented in the soil and bedrock.

And vines have pretty much the same requirements to photosynthesise wherever they are, and soil can be managed to provide these: liming an acid soil, adding drainage to soil in a region of high rainfall. Van Leeuwen says: “If wine quality was related to specific minerals such as potassium, phosphorus, iron and trace elements, then quality could be improved by the addition of these elements. But viticultural practice shows that, except for the correction of severe deficiencies or the application of excessive fertilisation, wine quality is not easily manipulated in either way by these practices.”

The sulphide connection

Nonetheless, many nutrient-poor soils exist. Indeed the heritage of viticulture is on soils that were too poor or mountainous to
grow other crops. An indirect relationship between poor soils, stressed vine growth, and winemaking may come into play, with winemaking accentuating or accessing a terroir effect.

Winemaking consultant Sam Harrop MW comments: “In Pouilly-Fumé, if you bang two bits of silex together, you get an aroma reminiscent of gunflint. Locals believe these flavours come through in the wine and I’ve tasted plenty of wines from this region with such aromas.  But a sulphide is responsible for this aroma, which occurs during fermentation, so the relationship of terroir and minerality is an indirect one. You can’t get the smell of silex banging together directly into the final wine.”

In addition, he says, winemakers in the classic Loire Sauvignon Blanc regions “have a less interventionist approach – for example, spontaneous fermentation, extended lees contact, not using nutrient supplement – and working with more turbid juices, which offer a greater concentration of precursors for thiol production. All of these work towards greater sulphides some of which can be really positive, and others not quite so tasty. For example, I see guava-like thiol expression from ferments of well-managed turbid musts.” So thiols are terroir-originated, and expressed by a well-managed fermentation process.

Fischer agrees, adding minerality is “more related to terroir than winemaking, though winemaking has an impact.  It seems to be a reductive character, so keeping wine longer on lees enhances the mineral character”.

A thiol called benzenemethanethiol has been reported by Denis Dubourdieu and colleagues at the University of Bordeaux as one source of a mineral/flinty note in Sauvignon Blanc. Parr says: “It is assumed that these thiols develop their flavour characteristics during fermentation as the precursor compounds in the grape itself need yeast to produce the thiol and the volatile aspects.”

While there’s a long way to go, minerality clearly does exist sensorially, though current industry usage of the term is highly individual, and without shared meaning. Until more is known, its use as a means of communication may advisedly be used only under caution.

Saly Easton MW, May 2009 (This article first appeared in the May 2009 edition of the drinks business)