soilOne of the most interesting debates in the wine world today is the debate over minerality. Does it exist? What is it? and Where does it come from?

The term “minerality” is relatively new to the wine world. It does not appear in Ann Noble’s influential flavor wheel developed at UC Davis in 1984. It does not appear in any of the canonical wine manuals that have formed our modern wine tasting practices such as Peynaud or Broadbent. It appears in the Oxford Companion to Wine only in the most recent edition. Yet it now appears routinely in the Wine Spectator’s tasting notes.

I find it to be one of the more useful terms for describing wine although I think it refers to many different taste experiences. The burnt matchstick flavors of Chablis, the aromas of wet stone in a good Riesling, the crushed rock aromas of a Willamette Valley Pinot Noir, and the iron filing notes of a Left Bank Bordeaux all can be described as falling under the general category of “mineral”.

But many people, especially wine scientists, dismiss the term as romantic nonsense, in part because, when the term gained currency, it was thought those mineral flavors in wine were the direct result of minerals in the soil being transferred to the wine. And indeed there is no evidence of that. Most minerals in soil have no flavor and although the roots of grapevines take up trace minerals from the soil, these do not appear to be transferred to the grapes. Wine also contains minerals such as potassium, calcium, and magnesium but these are not transferred from the soil and they also may not directly influence flavor. So there is skepticism about whether what we’re tasting has anything to do with actual minerals. On the other hand, we know soil has significant impact on flavor and we cannot rule out an indirect impact on flavor.

Despite this skepticism there is evidence that what we are tasting is real and rooted in features of the wine. Two studies described in this paper by Palacios and Molina are especially interesting. Researchers gathered two tasting panels of professional wine tasters and winemakers to taste wines selected for their minerality. After assessing the wines for their degree of minerality, the wines with the highest levels were analyzed for chemical compounds and the statistical analysis showed that high levels of perceived minerality were correlated with higher levels of free sulfur dioxide, low PH, and high total acidity with a variety of other compounds playing a less decisive, contributory role.

In a followup study, two tasting panels were given synthetic “wines” containing a variety of the previously identified compounds that seemed to effect minerality. In blind tastings using discrimination tests, the tasters were first asked to simply describe the “wines” with no knowledge of the purpose of the experiment. Then, in a second tasting, there were asked to specifically look for minerality. The purpose was to see which compounds produced the most significant perceptions of minerality.

The results:

…the presence of Succinic acid and a low pH combined with high levels of free sulfur dioxide are directly related to the use of the term minerality with a probability of 95%. The presence of Ethylphenols, m-Cresol and metals obtained a significance of 99% to relate as minerality in wine. Finally, with the same probability appears the compound Geosmin. Also the presence of Isoamyl acetate and Thiols is directly related in 99.9% with the emergence of the term minerality for the panel of producers winemakers…

Apparently there are many sources of what we call “minerality” and its perception is the result of the synergistic effect of many compounds as well as the absence of fruitiness which can cover up minerality.

At our session on minerality at the SWE conference conducted by Roger Bohmrich MW there was widespread agreement that wine such as Domaine Patrick Baudouin Anjou “Effusion”, Fritsch Grüner Veltliner “Steinberg”, and Christian Moreau Père & Fils Chablis all exhibited minerality.

Minerality may not be a direct transfer of flavor from soil to wine but there appears to be a consensus emerging that it is a useful descriptor with a foundation in the chemistry of the wine.