Tuesday, June 18, 2013

Minerality in wine? Fuggedaboudit

Or so says Alex Maltman of the Institute of Geography and Earth Sciences, Aberystwyth University, Wales.

In a previous post, I outlined a battle revolving around the role of soils in wine quality/typicity. Alex Maltman (Role of Vineyard Geology in Wine Typicity, Journal of Wine Research 19 (1), 2008) noted that it had become de riguer, when describing a vineyard, to specify its geology and this, coupled with the geological indications common in tasting notes, has served to infer "... a direct link between the vineyard substrate and the resulting wine." According to Maltman:
Such perceptions bolster a valuable tactic for the wine trade, as, being one of the few aspects of wine production that cannot be translocated or easily replicated elsewhere, a vineyard's geology is something that can be invoked to promote a wine's typicity, to give it a marketable uniqueness.
In a follow-up article (Minerality in Wine: A geological perspective, Journal of Wine Research, 2013), Maltman has honed in on minerality, a thoroughly modern (according to him) invention which had received no mention in the works of the "masters" (Peynaud 1987, and Vine 1997, for example) or the science-based tasting schemes (Jackson 2009 and Noble et al., Aroma Wheel 1987, for example). Maltman's 2008 and 2013 articles are built around a similar core argument but in the 2013 article, in addition to focusing on minerality, he advances explanations as to what tasters could be confusing with minerality. The latter aspect of his research will be dealt with in a later post.

There is, in general, a lack of understanding of the differences between minerals in foodstuff (of which wine is a part) and geological minerals (Maltman).

While it is true that the vine plant needs a variety of mineral nutrients, and that weathered bedrock is the source of much of these nutrients, the path from geological mineral to nutrient mineral is a protracted, rocky, and time-variant road.

To illustrate the latter point, Maltman uses the example of feldspar, the most commen geological mineral resident in modern vineyards. Feldspar is a family of minerals containing various combinations of minerals that are "ionically and covalently bonded into a crystalline lattice that gives a grain of feldspar strength and rigidity." This feldspar particle is bound together with a number of other mineral grains to form the aggregate we call rock or, in its fractured form, stone. The minerals contained in feldspar are not directly accessible by the vine plant. To be accessible by the plant the minerals have to be ionic and in solution. The process of transformation from the geological mineral feldspar to vine-accessible mineral nutrients is illustrated below.

Source: geology.csupomona.edu

Source: letslearngeology.com
The gulf between the vineyard chemical profile and that of the wine is further widened as a result of vine activity. The amount of nutrient ions absorbed by the vine roots is not directly related to the amount of nutrient ions in the soil. Rather, it is dependent on the transportation proteins and cell wall hydrophobic deposits among other factors. Further, once in the xylem, differential amounts of ions are directed to the various components of the vine architecture. Even within the berries there is a differential allocation of ions between, skin, seeds, and juice (Maltman 2013).

The disconnect grows even wider once cellar activities commence (shown below) and, as a result, the "proportion of mineral nutrients in finished wine bears only a complex, indirect, and distant relationship with geological minerals in the vineyard" (Maltman 2013).

After establishing a less-than-tenuous relationship between vineyard minerals and the mineral-nutrient signature of the finished wine, Maltman goes on to argue that minerality, as such, cannot be tasted in a wine. First, he argues, the concentration of inorganic material, in general, and mineral elements, in particular, in wine is miniscule -- between 0.15 and 0.4% for inorganics and very low levels for the mineral elements. Of the minerals, potassium has the largest concentration at 577 ppm (.06%) while calcium ranges between 30 and 200 ppm and magnesium registers at .005 ppm. Of the 50 organic elements identified in wine, 25 are trace elements (1 - 100 ppm) while 20 are ultra-trace (parts/trillion).

Compounding their relative scarcity in wine, these mineral elements have no flavor, a situation that also holds for geological minerals which are both solid and insoluble. Flavor-detecting organs in the mouth can only deal with solutions thus only sodium chloride, of all the geological minerals, registers a flavor in the mouth (Maltman).

So mineral nutrients resident in wine occurs in small amounts and are lacking in flavor. Vineyard geological minerals are flavor-free and would not register a taste in the human mouth. Aroma, the other component of flavor, requires volatilization in order to register on the organs on the olfactory bulb but neither rocks nor minerals possess this capability. Minerality as a taste descriptor, then, requires a leap of faith on the part of the taster.

How about texture, you ask? The geological minerals that existed at the beginning of the journey have been transformed beyond recognition in that they now exist as ions, rather than compounds, and in extremely small quantities. Any minerality imbuing capability would have to survive the journey detailed above and still have enough "surviving energy" in order to "infect" the completed wine in such a way that it exhibits "minerality" in a uniform manner.

Does Maltman's analysis consign minerality to the scrap heap of taste descriptors? Let me know your thoughts.

©Wine -- Mise en abyme


  1. We've all had wines with chalky, flinty, steely, earthy or other "mineral" characteristics. Putting those things into a wine wouldn't make it taste that way, so it's likely those characteristics arise in complex ways, and not necessarily from the soil being chalky, flinty, steely or earthy. Still, they're useful terms for describing wine.

    It's clear that grapes grown near Eucalyptus trees can pick up that character, so it doesn't seem a stretch that clouds of dust in the vineyard could have similar effects.

    1. Thank you for your comments.

      Chalkiness is an astringency term (Wine Business, Key wine components in mouthfeel components, November 2011, Bibiana Guerra). Chalkiness increases with greater tannin and in the presence of anthocyanins and is reduced with higher concentrations of ethanol and in the presence of acidic polysaccharides.

      Mr. Maltman addressed these other "mineral" characteristics in his article and I will cover them in my next post

  2. It would seem that the evidence if fairly strong against the case of an actual presence of minerals or their various sub-straits in wine. However, I would postulate that to the average consumer many "leaps of faith" are required when reading about descriptors as most people (myself included) often do not taste what they read or hear. I believe I have tasted what my brain believes to be a flinty or limestone characteristic in a wine, and many more descriptors that could be described as "minerality". As for other characteristics in wine it is my understanding that a vast majority of the "flavors" or various compounds detected by humans exist in wine itself. Since wine is hardly a static beverage I would venture to say that many of the compounds in wine could possibly combined to form what many perceive as a Mineral characteristic. I suppose only much more research and a lot of tasting will tell!