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vendredi, 31 mai 2013

MINERALITY IN WINE

MINERALITY IN WINE : MYTH OR REALITY


Claude Gilois

 

I was recently asked to define minerality in wine during a tasting of white wines. It is not easy to explain this concept whose meaning is vague and highly controversial. This subject is largely absent from wine literature although virtually all top tasters use it in their tasting notes. The debate about minerality in wine has been ongoing for several years, mostly on blogs and most  arguments are more empirical than scientific. However, there is some scientific evidence that can cast a light on this concept and allow us to start understanding minerality in wine.

 

 

 

 What can we learn from water about minerality?

 

The concept of minerality is easier to understand with water, in particular water coming from sources, as minerals present in water from underground sources come from aquifers where the water has been in contact with the bedrock often for several decades or even centuries imparting minerals into the water. The main minerals in water are calcium, sodium, potassium, iron, magnesium, phosphorous and sulphur. In general the  more minerals the water contains, the more taste it has. Water with a high mineral content can sometimes be described as metallic and a  little  mineral concentration will give a neutral water without much taste.  At optimum concentration, minerals give body and voluptuous characteristics to water. You only need to taste distilled water or water produced by reverse osmosis to conclude that water without minerals is undrinkable and that they are essential.   

 

NB: When you organise a wine tasting ensure that you have the most neutral water that you can get as you are tasting wine not water.

 

Can minerality be related to the soil content?

 

It is on this point that the controversy is most acute. Many observers and wine lovers dismiss that there is any relation between the two, intuitively this is hard to believe. For example, if we take an Assyrtiko from vineyards on Santorini island you can taste the volcanic rock upon which they grow. This is why most producers tame down this component with a maturation in wood to make it more acceptable to  customers. This ‘wild’ minerality is not without resemblance to some waters with high concentrations of minerals such as water from aquifers under Mount Fuji at more than 300 feet deep. If you look at the wine on Santorini, there is not much apart from the volcanic soil and the vines that grow on it. The organoleptic characteristics of an Assyrtiko elaborated in inox are sometimes described as ‘telluric’ such is its intensity. And what about Chablis where you can find a taste of stone and whose soil is very chalky ? We know that the erosion of chalky soils produces minerals in particular calcium and magnesium, There is also  the Loire Valley wines with vines grown on schist, granitic substrates and chalk and of course there are the Alsatian and Moselle wines. This list is not exhaustive.

 

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 Vineyard of Assyrtiko on Santorini

 

By and large, vines are planted on poor soil rich in stones. They receive between 400 and 1000 mm of rain a year and it is therefore not surprising that there is a mineralisation of the soil as time goes by that is to be found ultimately in the wine. It is worth noting that vineyards that need irrigation produce wines with less minerality than those where  water is provided naturally.

If we deny that the composition of the soil has a bearing on the taste of   the wine then a terroir based philosophy of wine, of which soil is a major component, loses its meaning.

 

Does minerality in wine come from fermentation?

This is the what Denis Dubourdieu and his team are arguing at the University of Bordeaux. Here, we are on scientific ground and not on empirical interpretation. They have demonstrated that during reductive  fermentation (without oxygen), sulphured aromatic components are formed. Some of them have negative effects on wine and bring vegetal characteristics, of which cabbage seems to be the most identifiable component  and they  can even render wine unfit for  consumption when Mercaptan[1] is formed. On the other hand, some of these sulphured components not only contribute to the varietal characteristics of white grapes but also provide its mineral characteristics. Dubourdieu et al identify two major components of prime importance, methoxypyrazine and a group of compounds called thiols[2], one of which being  benzenemethanethiol. It is this compound that confers the mineral characteristics to wine and they express themselves as gun, gunflint, somekiness or the smell of sulphur when you scratch a match. These are  terms to be used to express minerality in wine.

  

Is there a link between minerality, soil and vinification ?

 

We know that white cultivars give their best results on stony soils (Schist, Granite, Chalk, Silica and Quartz). These soils are poor and deficient in nutrients, in particular nitrogen.  It is the lack of nitrogen that forces yeasts to use substances, in particular aminoacids and produce  benzenemethanethiol as a by-product confering the mineral characteristics to the wine. It is a rather elegant theory as it would provide a convenient linkage between soil, vinification and wine. This has been proposed by  Filip Verheyden, the editor of the Belgium magazine Tong. This theory seems to be substantiated by observation of viticulturists and winemakers in New Zealand and  have been reported by Jamie Goode[3] in his book: ‘The Science of Sauvignon Blanc’[i] (p 80). They have noted that Sauvignon planted on new soils gave broader, more fruit driven,  massive and less mineral wines than those that had been planted for several years or decades and in which the content of nitrogen in the soil was lower.

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0ther elements that contribute to the minerality of  wine

 

Acidity: Is not as such a component of minerality but enhances it.

 

Salinity: Is a term that is very often used as a marker of minerality by salinity produced by the formation of sodium chloride that is derived from chlorine which is a trace element and not a mineral. Sodium chloride is formed, either naturally, as in Manzanilla from Saluncar de Barrameda in Jerez (next to the sea) or by irrigating wines with water with a high concentration of salt as in the Indian vineyards of Nashik. Saltiness cannot be considered as a marker of minerality in wine.

 

Concentration in methoxypyrazine: Is the component that imparts the green pepper, herbaceous, fresh cut grass element to the wine in particular to Sauvignon Blanc. Like acidity it amplifies the minerality but cannot be considered as part of it.

 

 

 

Does minerality exist in red wine?

 

There is no doubt that minerality is also present in red wines and that terms such as graphite and pencil lead are good descriptors of minerality in wines which contain Cabernet Sauvignon. Red cultivars are perhaps less systematically planted in stony soil, but wines from the Douro Valley that come from vines planted on schist have a definite mineral component to them.  However, it is worth noting that the increase in alcohol content of  wines (either due to anthropic global warming or to later picking) combined with lower acidity have the tendency to mask minerality in red wines….. It is a pity.

 

However,  red wines made near the Etna Volcano in Sicilia have a distinctive metallic minerality, which is not without resembling  that of the 'telluric' minerality found in  Assyrtiko.

 

 

 

 

 

 

 

 

 



[1] Also known as Methanethiol or methylmercaptan is a thiol  and  a colourless gas with a smell like rotten eggs. Source Wikipedia.

[2] In organic chemistry  thiols are  organo-sulphur compounds.

[3]Jamie Goode is an English wine writer with a scientific background and has a PhD in Plant Biology and worked as a science editor for 15 years. His latest book: Authentic Wine: Towards Natural and Sustainable Winemaking’ (2011, University of California Press) written in conjunction with Sam Harrop, MW, is a must for those wanting to understand the new developments  in winegrowing and winemaking.

 

 



[i]  Jamie Goode. The Science of Sauvignon Blanc (2012) Flavour Press. ISBN: 978-0-9553035-2-4.


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