Given the arguments summarised above, the question that arises naturally is: What are people tasting that they want to describe as mineral? This section reviews attempts at deconstructing the sensorial experience of minerality in wine; that is, at trying to understand just what it is that tasters are tasting.
4.1. Empirical Investigations
Several early studies employing mineral as a wine attribute explored the distinctiveness of Sauvignon blanc wines as a function of wine origin [45
]. Despite the lack of a clear definition of minerality for study participants, non-random results were reported. Parr and colleagues [45
] and Green and colleagues [48
] both reported that Sauvignon blanc wines from France (St Bris; Loire) were judged as more mineral than New Zealand (NZ) wines and in the case of the latter study [48
], that French wines were also considered more mineral than Austrian wines. In Lund and colleagues’ study [46
], perceived minerality allowed differentiation of French and South-African wines from NZ wines.
Two other studies in which mineral character was judged by tasters involved the wine variety Riesling. An early study [49
] showed a significant effect of judgments to the aroma descriptor mineral/flint in Canadian Rieslings. A second study, also employing Riesling [50
], showed that the attribute mineral explained part of the difference between wines made in slate and sandstone bedrocks from those made in other bedrocks such as limestone, sandstone or basalt. Interestingly, two only of the sensory studies reported above used a physical reference for minerality for pre-experimental training purposes [46
]. These research teams both employed a benzenemethanethiol (BMT) solution as a minerality reference, while the other studies relied on participants’ internal, idiosyncratic representations [45
], allowing for flexibility in definition of this attribute.
One of the first scientific investigations aimed specifically at understanding the sensorial nature of mineral character in wine was reported by Ballester and colleagues [2
]. The study included both a conceptual and linguistic component (already described in Section 2.1
above), as well as a perceptual (sensory) component. Using Burgundy Chardonnays as wine stimuli for the sensory component, researchers asked wine professionals to rate intensity of mineral character orthonasally (nose only) and subsequently by palate only in a tasting condition where the tasters wore nose clips to minimise retronasal olfaction effects. Wine professionals reported experiencing minerality in both conditions, i.e., orthonasally and by palate only. However, there were substantial between-panellist differences amongst the wine professionals in terms of which wines were judged as most and least mineral in both conditions. To determine the wine sensory characteristics associating with perceived minerality, the wine professionals’ minerality intensity ratings were associated statistically with sensory characterisation of the Chardonnay wines that had been undertaken by trained panellists. Results showed the wine professionals to clump into three groups in each condition (smell only; palate only) based on the sensory characteristics they associated with minerality. Of particular interest in terms of supporting anecdotal evidence, lack of fruit, gunflint and reductive aromas were correlated with minerality judgments for two of the three groups of tasters in the smell-only condition, while in the palate-only condition, perceived acidity and bitterness were important to minerality judgments for two of the three groups of tasters.
Not much later, Heymann and colleagues [51
] published work on the topic. These authors also employed wine professionals and trained panellists to investigate the concept of minerality, this time in a range of white wines (Chardonnay; Riesling; Pinot gris; Sauvignon blanc). The participant groups undertook different sensory tasks, with projective mapping of the wines undertaken by wine professionals, whilst the trained panellists undertook a standard, descriptive analysis task. Several results are noteworthy.
First, wine variety was a factor in judgments of mineral character with the Riesling, Pinot gris and Sauvignon blanc wines on average reported as more mineral than the Chardonnay wines, the latter judged as exhibiting qualities suggestive of oak and malo-lactic fermentation (MLF) influences, these associating negatively with the term mineral. This is an interesting, somewhat unexpected, result given that two of the four Chardonnay wines were Burgundian with the wine from Chablis associating more with notes of butter than with mineral character in the experts’ data ([51
]: figure 1, p. 7). Second, taking into account the data from both participant groups, several descriptors associated positively and others negatively with perceived mineral character. For wine professionals, minerality associated positively with citrus, fresh, wet stones and acid terms, while for trained panellists mineral associated positively with chalky, reduced, grassy aromas and bitter taste. Negative associations for both groups involved the characters associated with oak influence and MLF (e.g., butter; creamy). In addition, fruity and sweet notes were negatively associated with mineral for the trained panellists. Finally, the lack of consensus in judgments of mineral intensity in the wines reported by Ballester and colleagues [2
] was supported by Heymann and colleagues’ [51
] data, which showed major between-panellist, group differences in ranking of mineral character to several of the aromatic varietal wines (Sauvignon blanc; Riesling; Pinot gris). The authors interpreted these between-group differences as reflecting perception-mode differences; their wine professionals utilised both smell and taste and were driven by acid taste in their mineral judgments, whereas the data suggested that the trained panellists’ mineral judgments involved aroma only and not taste.
In a more cognitively-oriented study, [43
] researchers asked whether minerality in wine is a sensorial reality or primarily a mental construct. That is, they asked whether their 63 experienced tasters (wine professionals) were perceiving something in wine via data-driven perception, evoking memories of soils, earthy notes, stones, and so forth, or whether their judgments of mineral character in the wines were primarily based on information already stored in the taster’s head, the latter known as top-down information processing [52
]. Arguing that consensus across tasters from different cultures in their qualitative, perceived minerality judgments would most likely indicate data-driven cognitive processing (i.e., judgments based on actual tasting of the wines, rather than on top-down cognitive processing), Parr and colleagues [43
] asked French and NZ wine professionals to judge intensity of a range of wine attributes including minerality. The wines employed in the study were a selection of French and NZ Sauvignon blanc wines, some of which had received wine-industry judgments as expressing mineral character. This study extended prior work [2
] by investigating cross-cultural phenomena and by employing a within-subject, procedural component where each participant from both cultures (France; NZ) undertook each task (sorting and descriptive rating). Descriptive ratings to the wines occurred under three, separate perception-mode conditions for each taster: orthonasal (nose only); palate only (taste; trigeminal stimulation); global perception (orthonasal, retronasal, taste, trigeminal).
Parr and colleagues [43
] also tested several hypotheses with their bases either in anecdotal reports of potential sources of perceived minerality [53
], or in prior research findings [2
]. The hypotheses implicated the roles of perceived acidity, reductive phenomena, perceived stony/soil notes and relative absence of fruity notes in driving judgments of mineral character in Sauvignon blanc wines. Results demonstrated that both French and NZ wine professionals reported minerality via each perception mode; that is, orthonasally, retronasally and on the palate (taste and trigeminal stimulation). An interesting cross-cultural, cross-modal effect occurred with respect to minerality intensity judgments with olfaction contributing more to the judgments of French participants than NZ participants, the latter employing palate phenomena and olfaction more equally. Sorting task data demonstrated a remarkable consistency across cultures, with both French and NZ tasters largely separating the French wines from the NZ wines. Overall, the descriptive rating results also showed more similarities than differences indicating substantial cross-cultural consensus in terms of how minerality was perceived qualitatively in the French and NZ Sauvignon blanc wines. There was more cross-cultural consistency in perception modes of orthonasal and palate only than when retronasal judgments were made. Parr and colleagues [43
] interpreted the substantial degree of cross-cultural consistency as providing evidence of data-driven cognitive processing and suggestive of a shared cognitive structure amongst wine professionals concerning the concept of minerality in Sauvignon blanc wine, with domain-specific expertise over-shadowing any culture-specific differences that could result from France and NZ having very different wine-production histories [54
To summarise the wine description data [43
], and taking all perception modes into account, the important positive predictors of minerality in the wines were attributes of citrus, fresh/zingy, bitter, flinty/smoky, chalky/calcareous and liking. Important negative predictors were fruity (passionfruit; green character), sweetness and most interestingly the taste of sourness (acid). Counter to the authors’ hypothesis, reductive notes did not associate statistically with mineral in this study. These descriptive rating data show many similarities to, but also some important differences from, those of Heymann and colleagues [51
] in terms of wine characteristics associating with the concept of mineral. Consistent across the studies were citrus, fresh/zingy, chalky and bitter taste associating positively with mineral, while fruity notes and sweetness negatively associated with mineral character. There were however some differences, with Heymann and colleagues [51
] reporting reduced as positively associated with mineral by their trained panellists, while reductive notes (e.g., sulphide) were not significantly associated with perceived minerality in the wine professionals’ data reported by Parr and colleagues [43
]. Other important differences concern acidity where acid taste was a positive predictor of mineral character for Heymann and colleagues’ tasters [51
], whereas Parr and colleagues [43
] report sourness/acid taste as a negative predictor of minerality for both French and NZ wine professionals. Clearly, further research involving various wine varieties is needed to clarify the attributes important to the internal structure of the abstract notion of perceived minerality in wine.
] recently extended others’ work [43
] to investigation of several white (Godello, Riesling, Sauvignon blanc, Treixadura, Ribolla and Grenache gris) and red varieties (Tempranillo, Blaufrankisch, Syrah, Poulsard and Grenache noir). The study also compared two panels of wine professionals with different types of domain-specific expertise (wine producers from La Rioja vs. wine merchants and sommeliers from Barcelona) in two conditions, nose only (orthonasal olfaction) and full tasting. The main results reported showed that both panels found significant differences between white wines in terms of their mineral intensity, but no significant effect was found for red wines. Interestingly, the minerality average score for red wines was significantly lower than that for white wines for the wine merchants/sommeliers’ panel. Concerning the results for white wines, orthonasal minerality scores from both panels were significantly correlated with three Rieslings the most mineral wines of the sample set. Minerality differences in the full tasting condition were significant only for the wine producers. However, nose only and full tasting condition scores were not significantly correlated for wine producers. The same panellists carried out a sensory profile on the samples, the data used to predict minerality scores from the sensory attributes. The merchant/sommeliers’ data did not produce any robust regression model on white wines. On the other hand, the wine producers’ data yielded a robust regression model only for full tasting minerality scores. The negative predictors of minerality were tannin concentration (used here as a sensory descriptor) and balance, while the data concerning positive predictors showed unexpected results. More specifically, for the first time sweetness and alcohol were found to be positive predictors for minerality. More in keeping with prior research, acidity, palate weight and bitterness were also positive predictors [43
Taking a somewhat different approach to investigating perceived minerality in white wine [55
], Rodrigues and colleagues limited their study to the specific variant of Chardonnay table wine produced in the Burgundian region of Chablis and focused on influence of vineyard location. The wines of Chablis are often reported as flinty by wine producers and wine critics [56
], with their terroir or origin implicated, in particular the vineyard soil types (e.g., Kimmeridgean marl), fossils and river bank (left or right side of the Serein River). Right-bank wines tend to be described as softer and fruitier, while left-bank wines exhibit a fresh, zingy note [57
]. In their study, Rodrigues and colleagues [55
] investigated sensory and chemical aspects of minerality in Chablis wines as a function of vineyard location (left vs. right river bank), finding that their orthonasal sensory data showed a significant effect of vineyard location with left-bank wines reported as more mineral than right-bank wines. No such effect was demonstrated in the full tasting condition.