What is minerality in wine? What are we experiencing when we label wine attributes as “mineral?”

Despite frequent current usage, the term mineral as a wine descriptor reflects a relatively recent fashion, for which the term appears to have no clear definition.^1,2 When white wines are described sensorially in terms of mineral characteristics, the attributes employed are multi-dimensional, meaning they involve smells, tastes and tactile sensations. Further, they range from stone and soil-related terms (e.g., flinty; wet stones), seashore terms (e.g., iodine and seashell), smoky and gunflint notes, tastes of acidity, bitterness and saltiness, to the kerosene-like notes in Rieslings.²

The sole clear and consistent aspect is that perceived minerality in a wine appears favorable in terms of wine marketing, with perceived minerality linked to higher priced wines. Conceivably this is because wine characteristics interpreted by tasters as mineral (such as flinty, chalky or oyster shell) have an ability to evoke wider concepts via associative memory including the powerful marketing tool of vineyard location, or terroir.^1,2

However, with many viticulturists and more recently geologists including Alex Maltman3 arguing that we cannot literally be smelling or tasting the vineyard rocks and soils, the question arises: What are we experiencing that induces us to use terms pertaining to rocks and soil when describing attributes of a wine?

Maltman, a professor of earth sciences at Aberystwyth University in Wales, outlined in a recent talk⁹ at the Institute of Masters of Wine in London, UK, the disconnect between geological minerals (elements) and the 14 mineral nutrients required by vines, pointing out that “these 14 are not the same minerals as geological minerals.”

“Elements are not necessarily bioavailable.…Weathering processes are too slow to keep pace releasing nutrients for vegetation year after year, (and) the cycle is interrupted with agriculture. Nutrients are removed each year in crops, so we have to add compost, fertilizer.…Most of the nutrients are coming from humans, not the geology,” he explained.

Added to the conundrum is that minerals do not vaporize. They are odorless, and their concentration in wine is far below the taste threshold. This latter point, however, must be qualified in that sub-threshold tastes and smells have been demonstrated to interact to produce an experience of “flavor.”⁴

Is minerality in wine all in the mind?
If we are not tasting soils and rocks, then what are we tasting? Is the flavor that we describe as “mineral” all in the mind? In one sense, yes. This is because a wine’s flavor is not in the wine but in our brain or mind.5 Flavor is a multi-modal percept created in the brain from wine. That is, when we smell or taste a wine, it is the brain that integrates the various sensory inputs that the wine’s composition affords. This is accomplished via the processes of perception. Perception of a wine’s attributes is a complex process involving sensory input via our visual, olfactory (smell by nose; aroma by retro-nasal olfaction), gustatory (taste) and mouthfeel systems. In addition, the context within which we experience a wine (at the vineyard or in a restaurant) can further influence our perception and conceptualization of a wine.⁵

Is minerality in wine a sensorial reality or a mental construct?
The question is whether there is something we are perceiving in wine that is evocative of stones, rocks and so forth, or whether we draw primarily on ideas and information already stored in our heads, perhaps as a result of clever marketing (top-down or knowledge-based perception), when we employ mineral characteristics to describe what we are experiencing in a wine.

An example of top-down perception is when memory of chalky soils and fossils observed when visiting a vineyard could bias a taster to actually “taste” mineral characteristics in a wine from a particular vineyard just as color has been shown to bias us to smell red wine characters in white wines that have been colored red with odorless anthocyanin.⁵

When we taste a wine, two sources of perceptual information can contribute to what we experience. The first is known as data-driven perception, or information processing, and relates to sensory input pertaining to the objective properties of the wine—that is, to what is actually in the glass.

However, perception is not a one-way process, and the second source of input, termed top-down or knowledge-based information processing, reflects this. Top-down perceptual processing concerns how what is already in our head when we experience a wine (our expectations, ideas and emotions) can interact with the data-driven sensory input to influence what we perceive and how we end up conceptualizing and describing a wine.

In other words, our prior experience, which is unique to each of us and comprises our ideas, memories, knowledge, expectations, familiarity and so forth with the wine being tasted—along with our mood and emotions—can influence how we perceive any particular wine sample at any point in time so that our subjective view of a wine may deviate greatly from a more objective view.⁶ This process occurs effortlessly and can be outside our conscious awareness.

The perceptual processes described above are highly relevant to understanding more abstract aspects of wine appreciation such as perceived complexity, quality and minerality. Within a collaborative project involving French and New Zealand scientists, we investigated the nature of perceived minerality in Sauvignon Blanc wines with particular interest in the following question: Is minerality in wine a sensorial reality or primarily a mental construction? Are there characteristics in wine that evoke memories or images of stones and rocks? Or are we drawing primarily on top-down information already stored in our heads when we employ mineral characteristics as wine descriptors?

The latter option should result in more idiosyncratic responses by tasters than the first option, given that what is stored in our heads is unique to each individual taster, whereas data-driven input based on the objective properties of the wine sample should result in somewhat more consistent responses from tasters.

Investigation of perceived minerality in Sauvignon Blanc
The Sauvignon Blanc experiment involved a cross-cultural comparison where 63 wine professionals (31 New Zealanders and 32 French) assessed 100% Sauvignon wines from France and New Zealand in terms of minerality and other wine attributes.7 The 16 wines selected for tasting had been judged by their producers as reflecting their source of origin and vintage (2010), with approximately half having been judged a priori by wine critics as exhibiting mineral characters and the other half not so.

To investigate a specific issue currently of much interest (namely whether an expression of mineral can be smelled or whether it is a palate sensation only), we asked each judge to assess the wines three times under the following conditions: nose only (ortho-nasal olfaction), palate only (taste and trigeminal stimulation/mouthfeel) called the nose-clip condition, and by full tasting (smell by ortho-nasal olfaction and aromas by retronasal olfaction, taste and mouthfeel). The Sauvignon Blanc wines were subjected to extensive physicochemical analyses, although these data are reported elsewhere.⁸

In addition to trying to shed light on the debate as to whether minerality can be smelled or not, we considered other questions arising from anecdotal evidence and media reports concerning perception of mineral character in wine. Of particular interest was the role(s) that perceived acidity, reductive phenomena and relative absence of fruity characteristics in a wine play in driving judgments of mineral character.

We asked the tasters to assess a range of attributes in each wine, comprising five Sauvignon flavor characteristics (herbaceous, boxwood, citrus, green and passion fruit), three tastes (sweetness, bitterness and sourness), five descriptor classes involving terms often used to refer to minerality within the wine industry and scientific literature (flinty/stony/smoky, chalky, iodine/oyster shell, pencil/graphite and matchstick/burnt rubber/sulfide), and six other characteristics (astringency, freshness, concentration, complexity, familiarity and appreciation of the wine. Appropriate descriptors only were rated in each perception mode condition.

What did we find?
When the French and New Zealand wine professionals rated minerality in each wine on a 100 mm horizontal intensity scale with “absent” at one end and “very strong” at the other, the French and New Zealand wines were judged similarly overall in terms of intensity of mineral character, with three New Zealand and four French wines being rated more highly than other wines in terms of intensity of mineral character.

The figure “Judgments of Mineral Intensity in French and New Zealand Wines” demonstrates this. The wines on the right side of the plot, where the vectors for perceived mineral intensity in each perception-mode are placed, were judged higher in mineral intensity than wines on the left side of the plot. There was no evidence to support the notion that New Zealand Sauvignon Blancs, being regarded as highly aromatic and fruity wines, were, on average, lower in perceived mineral character than the French wines in this particular study.

When the tasters described the wines, the French and New Zealand wines were perceived as different from each other by both French and New Zealand judges. Judges from both cultures reported the New Zealand Sauvignons as acidic and aromatically expressive in terms of herbaceous and fresh green notes. The French wines were considered floral, complex and well structured, with two verging on the faulty spectrum (such as oxidative or reductive notes).

Can you smell minerality?
Minerality was reported in wines from both cultures via each mode of perception, including by nose alone. Interestingly, one of the few significant cross-cultural differences demonstrated by the study showed the French judges relied more on their noses than the New Zealanders in their full tasting judgments of minerality. The New Zealand judges relied equally on olfaction (smelling) and on palate phenomena (taste and mouthfeel).

Which wine attributes predicted perceived minerality in the Sauvignon wines?
We conducted linear regression analysis, the results of which demonstrated that several specific wine characteristics associated statistically with perception of minerality in the wines, some consistent across mode of perception and consistent across cultures. Influence of culture produced more similarities than differences, suggesting that wine professionals have similar ideas about the structural content of the concept “mineral” as experienced in Sauvignon wines.

The table “Significant Predictors of Minerality for Each Culture by Olfaction” shows the wine characteristics that predicted judgments of minerality when the Sauvignon wines were assessed by nose only. The results in this table show relative consistency across cultures, with citrus notes, chalky/calcareous, flinty/smoky, lead/graphite and absence of passion fruit odor predicting perceived mineral judgments for both groups.

In each Table, T is the t statistic, and P refers to the probability of the result occurring by chance alone. All attributes reported in the tables were statistically significant. The attributes with a negative t value were inversely associated with minerality (i.e., absence of the particular wine attribute predicted minerality), while those with a positive t value were positively associated with minerality. Predictors are characteristics categorized in terms of the judges/tasters from France or New Zealand, not the wines.

The table “Significant Predictors of Minerality for Each Culture by Smell, Taste and Mouthfeel” shows that the full tasting condition, where smell, taste and mouthfeel sensations could play a part, produced more variable data across cultures. Characteristics predicting minerality that were consistent across cultures were citrus, bitter and chalky/calcareous. Absence of flavor (absence of passion fruit and sweet for the French; absence of green characters for New Zealanders) predicted mineral intensity in the wines.

The table “Significant Predictors of Minerality for Each Culture by Palate Only” shows the predicting characteristics in the palate-only condition. When sensing the wines’ aromatic qualities was inhibited (the judges wore nose clips), bringing palate sensations into focus, we see a consistency across cultures. A combination of mouthfeel sensations (fresh/zingy, palate weight) and taste (bitter, absence of sour and absence of sweet) were important predictors of perceived minerality in the wines.

To summarize the sensory study outcomes, our data showing many cultural similarities across two very different wine cultures suggest that judgments of minerality in Sauvignon wines appear to be based on data-driven input (actual wine characteristics) and not just on smart marketing (knowledge-based perception). Further, specific wine attributes (notably citrus notes and the fresh/zingy character of Sauvignon wines) were particularly important predictors of judgments of mineral intensity in the wines.

Which aspects of wine are implicated in perception?
This important question concerning which aspects of wine composition are implicated or associated with the perception of mineral characters in white wine has not escaped our endeavors. Reported elsewhere are wine composition data that have been associated statistically with the sensory data reported here in an attempt to elucidate the physicochemical source(s) of perceived minerality in Sauvignon Blanc wines.⁸

What can we conclude?
What is clear from our work to date is that mineral character in wine is perceived as an odor, a taste and a textural sensation by both French and New Zealand wine professionals, although there are qualitative differences across these modes of perception. That is, in showing that other specific wine attributes are associated with judgments of mineral intensity in a Sauvignon Blanc wine, we also demonstrate that these specific characters differed according to mode of perception (smell alone or full tasting). For example, absence of passion fruit was important in predicting minerality as judged on the nose, whereas the fresh/zingy character was the most important predictor of minerality as perceived on the palate.⁷

When looking at our various sensory studies about this topic, an interesting issue jumps out; it appears that wine varietal differences may influence how mineral character is perceived in a wine. It is clear that further work is required, including with other varieties such as Riesling, before we can say precisely which wine attributes form the basis of the sensorial reality of perceived minerality in white wines.

References
1. Easton, S. 2009 “Minerality.” Drinks Business, May 86-88.
2. Ballester, J., M. Mihnea, D. Peyron and D. Valentin. 2013 “Exploring minerality of Burgundy Chardonnay wines: a sensory approach with wine experts and trained panellists.” Aust. J. Grape Wine Res., 19, 140-152.
3. Maltman, A. 2013. “Minerality in wine: A geological perspective.” J. Wine Res., 24 (3), 169-181.
4. Dalton, P., N. Doolittle, H. Nagata and P. Breslin. 2000 “The merging of the senses: Integration of subthreshold taste and smell.” Nature Neuroscience, 3, 431-432.
5. Small, D.M. 2012 “Flavor is in the brain.” Physiology & Behavior, 107, 540-552.
6. Parr, W.V. 2015 “Making sense of wine: Cognitive psychology’s contribution to understanding wine tasting and wine tasters.” Proceeding of Oeno2015: 10th International Wine Symposium, Bordeaux, France, June 29 – July 1, 2015.
7. Parr, W.V, J. Ballester, D. Peyron, C. Grose and D. Valentin. 2015 “Perceived minerality in Sauvignon wines: Influence of culture and perception mode.” Food Quality & Preference, 41, 121-132.
8. Parr, W.V, D. Valentin, J. Breitmeyer, D. Peyron, P. Darriet, R. Sherlock, B. Robinson, D. Grose and J. Ballester. 2016 “Perceived minerality in Sauvignon blanc wine: Chemical reality or cultural construct?” Food Research International. 87, 168-179. DOI: 10.1016/j.foodres.2016.06.026.
9. “IMW SEMINAR DEBUNKS MINERALITY MYTHS.” www.thedrinksbusiness.com/2016/10/imw-seminar-debunks-minerality-myths/