As a descriptor, minerality didn’t crop up in the wine industries lexicon until the late 80s. In a recent Decanter article Prof. Alex Maltman recalled writing his first piece on the topic a little over 15 years ago. Maltman posits the term to be of ‘pragmatic usefulness’ despite there being no clear consensus on what it actually means. We wine-lovers are relentless in our often rather numinous linguistic translations of the perception and sensation of wine in to, more often than not, overtly simplistic terminology. Vast may this parlance be, minerality is arguably amongst the most ubiquitous of all its components. What makes minerality so challenging to define? How helpful is it? What do we know about the science? In this piece I explore the concept in more detail and piece together my own thoughts.
Much of the language used within the wine industry is in some sense metaphoric. Gordon Shepherd discusses this in detail in his book Neuronology: How the Brain Creates the Taste of Wine. Minerality in wine seems to have resisted this same rational. I’m not exactly sure why this is. One could argue that marketing efforts of those wishing to promote the idea of a region or place offering exclusivity have contributed.
Minerality is a particularly esoteric term, one which studies show is considered alien to those new to wine. Even amongst the more seasoned there is little accord. There are those who postulate minerality to be the literal taste of minerals absorbed by the vines root system. Meanwhile, others draw a more broad, loose and varied relationship between terroir, variety, climate and minerality. Alex Maltman’s ‘Problem with Minerality’ GuildSomm Podcast opened my eyes to the problems with the often-romanticised literal position.
Vineyard soil (topsoil, subsoil, bedrock) contains minerals, those associated with overall structure of soil and those absorbed by vines. Minerals associated with overall vineyard soil structure are complex ionic bonded aggregate compounds which are often rigid and insoluble. In order for positively-charged individual ions (known as cations) to become available a whole host of things must happen.
Known collectively as weathering and aided by the presence of both humus and the general microbiology, this complex set of processes may lead to the formation of clay minerals. In the case of nitrogen and phosphorus (essential for vine growth) both are entirely a product of this organic matter. These processes vary over time and are not stable. The pace at which they take place depends on factors such as soil temperature, acidity, humidity, microbiology and more. This level of variability puts in question the relationship of a common characteristic and processes lacking consistency and balance.
Grapevines require a variety of different minerals in order to successfully grow. Once made available, the roots absorb these minerals dependent on demand not availability. The root is not trawling the soil, instead it is carefully managing uptake. This uptake is suited to the vines needs and controlled via sophisticated evolved methods of absorption and filtration. Once absorbed, these minerals are indistinguishable in origin, regardless of its origin, to the vine magnesium is magnesium.
It is almost doctrinal that one should avoid mineral-rich overly fertile sites when planting vines. With this in mind, and given the grapevines relatively low nutrient requirement, selective uptake could suggest that in many cases the vine is not directly exposed to an abundance of any particular mineral. A vineyard with bedrock high in potassium may not result in a wine necessarily high in potassium. Instead the vine is driven by its own requirements, regardless of the vineyards makeup. Such method of uptake would mean be plausible to deduce characteristics based on the structure of vineyard soil.
These mechanisms are not perfect, it is possible for a more easily-absorbed mineral to fool a vines filter. This can result in increased uptake of this mineral compared to one less easily absorbed. Therefore, visible signs of a particular mineral deficiency, such as leaf yellowing, may not necessarily indicate a deficiency in the soil but instead a malfunction in the vines own absorption.
If soil-derived minerals were directly responsible for discernible aromatic properties in a finished wine, one could assume with some level of accuracy that almost all wines should display these characteristics. Interestingly, water tasters have shown that water becomes more disagreeable as mineral content increases. Perhaps a mineral-rich wine would not be so attractive after all.
Where minerals are present in a finished wine (some originating in the soil and some as a result of fermentation) Maltman notes the quantities present are likely to be well below the sensory threshold. Although more anecdotally, Olivier Humbrecht further supports this notion. Olivier has gone to considerable effort in an attempt to identify discernible characteristics in wines relating to specific soil types. After extensive tasting he is clear that the vast complexity of this task has meant he has been unsuccessful.
What I am not doing is denying any relationship between vineyard soil and a finished wine. Instead, I am proposing that this relationship is much more nuanced, indirect, complex and convoluted than we often portray. A number of indirect relationships between minerals and a vines development and finished wine characteristics exist. Examples are gene expression, canopy growth, yield and the nature of fermentation. Studies have shown that varying levels of N, K, Mg, Fe, and Zn do correlate positively with cluster number and weight. Where this is the case, an increased total yield, and thus altered style, would be expected.
Nitrogen acts as a growth controller. Excess nitrogen to the vine can encourage abundant canopy development. Left un-pruned this may well result in increased shading to the fruit zone. Studies have shown that increased shading will alter the expression of aroma compounds such as rotundone and TDN. Minerals do indeed affect the vines development; however, this is a complicated and variable process unlikely to result in a single reoccurring characteristic.
In a study assessing detection of minerality in wine by both smell and taste, the smell-only condition showed that two-thirds of the tasters correlated minerality with reductive aromas such as gunflint and lack of fruit. Howeve, with their noses clipped, roughly the same amount of tasters related minerality to acidity and bitterness. Studies out of Spain’s University of La Rioja have shown minerality to be most commonly associated with white wines, various other studies have shown that where tasters use both smell and taste to assess a wine, acidity is important in identifying and recognising minerality. Additionally it has been shown that varietal is an important indicator as to whether a finished wine will display minerality.
VitiSynth have produced two helpful Sankey diagrams, one showing aromas and aroma compounds with a positive correlation to minerality and another showing negatively correlated aromas and compounds (sometimes said to mask minerality) The whites tasted during the Hallgarten conversation all fell in to the category of high acid, minimal to no use of oak and less prominent primary or tropical fruit. The reds showed evidence of reduction, were also minimal intervention and also showed minimal to no use of oak. The aforementioned diagrams may help to better understand the perception of these wines as mineral.
Amongst these wines was an Argentinian Malbec. In some sense contrasted to conventional Argentinian Malbec the wine was subject to natural winemaking. This included spontaneous fermentation, extensive skin contact with exposure to solids and concrete egg fermentation. This set of practices would certainly be more likely to result in a wine with higher acid, less intrusive primary fruit and oak aromas and volatile sulfur compounds (reduction) Throughout their assessment of the wines the pair consistently described them as high acid, low tannin, fresh, saline and reductive. There was a distinct lack of the characteristics VitiSynth suggests ‘mask’ minerality (oak, intense fruits etc.) and an abundance of those which both VitiSynth and a large number of previous studies have shown correlate positively with the identification of a wine being mineral.
Many of the regions frequently reported to produce wines perceived as mineral do have something in common. Spoiler alert, it is not soil type, nor is it mineral content. All are fairly cool regions where both the most frequently planted variety and the climate support the production of wines which likely to display characteristics perceived as a mineral. During the Hallgarten conversation, Steve noted that in recent vintages (presumably as Sancerre has grown warmer) Silex (the famous wine of Didier Dagueneau) had ‘lost’ its minerality, this perhaps indicating that minerality is indeed more closely related to high acid and lack of dominant fruit opposed to any direct mineral content within the grape
Reduction is to some extent a wine fault; however, as is the case with several other ‘faults’ in small doses reductive wine making results produces aromatic compounds which are attractive and unique. Producers such as Coche and Roulot have mastered this style of winemaking. Denis Dubourdieu of the University of Bordeaux identified benzenedimethanethiol as a compound contributing to the gunflint aroma in white Burgundy and thus a potential source of perceived minerality. Mercaptans, ethyl mercaptan and diethyl sulfide are also volatile sulfur compounds responsible for aromas of rubber, burnt match and flint.
In 2016, Professor Pascale Deneulin conducted a survey of 2,000 French and Swiss wine professionals. The study showed strong association between perception of minerality and sulphur compounds. Almost 50% of tasters referred to gunflint or flint as their primary association with minerality. A number of other studies by Wendy Parr and Jordi Ballester have drawn association between varietal-specific perceived minerality and reduction. Key findings of further studies are that concentrations of both free and bound sulphur dioxide were positive indicators of perceived mineral character in the wines. Geoff Kruth notes that low Ph wines exacerbate reductive winemaking and are more likely to show signs of reduction. This could add weight to the argument that regional-specific characteristics and vineyard qualities may correlate with reduction and perceived minerality.
When describing wine, much of the sensory experience comes as a result of association. The way in which perceived minerality is associated with how a person expects something to taste is not fully understood. Nor is how the experience or memory they relate to that particular characteristics (minerals) in this example affects their experience. Perhaps when we describe Riesling as smelling or tasting like slate, opposed to being literal, we may in fact be exploring and sharing our minds formulation of what we believe slate would taste like were it to have a taste. An interesting thought.
In summary, opposed to elucidating a single particular aroma or characteristic, minerality is instead a broad and varied term. The wine industry seems to have adopted it in order to capture a wide range of characteristics and sensory experiences. These experiences may be related to a particular region, style or viticultural practise and as such help to categorise a wine. Clearly there are indirect and direct relationships between the soil and the vine. Despite this, it does not seem likely that much of what we perceive as minerality is derived directly from minerals found in soil. Opposed to a complex string of indirect relationships, perhaps the more rational position would be that the characteristics of a particular variety, absence of alternate characteristics and growing conditions could lead tasters to use a broad term to ‘fill in the blanks’.
Perhaps with time we will get closer to more accurately understanding exactly what minerality is. In the mean time it does make for great marketing …