Introduction

After water, ethanol is the second major component of wine. According to the official definition of wine proposed by the Organisation Internationale de la Vigne et du Vin (OIV) in 1973, its “actual alcohol content shall not be less than 8.5 % v/v” but might be reduced to 7.0 % v/v in specific cases. Even if no upper limit has been defined, the maximal ethanol content is mainly driven by the yeast’s fermentation ability, which typically does not exceed 15 to 16 % v/v, as well as often by financial penalties that can apply in some markets for high ethanol wines (Österberg, 2011).

Since the second part of the 20th century, many concerns have been raised about ethanol and there has been a convergence in policies across the European Union (Babor et al., 2010). Such policies - for example, the requirement to display the alcohol content along with health warnings on the label - are imposed as a result of its harmful effects on human health.

Over the same period of time, and as shown in a recent study conducted in Bordeaux and Napa (Gambetta and Kurtural, 2021), there has been an increase in grape sugar concentration and therefore in the final ethanol content of wine as a consequence of climate change, which has led to an increased cumulated annual growing degree days (GDD). For other wine regions that were traditionally dedicated to the mass production of entry level wines, such an increase in ethanol might have been amplified by the shift towards quality wines whose production involves better yield monitoring (Jackson and Lombard, 1993; Smart et al., 1990).

As global consumer demand has moved towards fruitier, lighter wines, and to match demand and supply that might be considered out of balance (Bucher et al., 2018), European regulations have evolved by authorising since 2009 the dealcoholisation of wines within the limit of -2 % v/v (EU Regulation N° 606/2009). For dealcoholisation over this limit, beverages must be named in accordance with the OIV International Code of Oenological Practices as “wines with alcohol content modified by dealcoholisation” for ethanol content above 8.5 % v/v; “beverages obtained by the partial dealcoholisation of wine” for ethanol content between 0.5 % and 8.5 % v/v; and “beverages obtained by the dealcoholisation of wine” for ethanol content less than 0.5 % v/v.

This dealcoholisation is generally achieved through physical processes based on membrane separation (i.e., nanofiltration, reverse osmosis) or thermal distillation (i.e., distillation, vacuum distillation, spinning cone column) (Pickering, 2000; Sam et al., 2021).

The impact of ethanol on the sensory profile of wine is well known and has been the subject of much research. High ethanol content generally decreases acid perception (Fischer and Noble, 1994) and aroma volatility, which makes wines particularly rich in ethanol seem less fruity (Conner et al., 1998; Escudero et al., 2007). The impact of ethanol on sweetness is still under debate, with some authors reporting an increase in sweet taste with an increase in ethanol (Martin and Pangborn, 1970; Scinska et al., 2000). More recent work found that the sweetness of dry wines was not affected by the usual variations in ethanol, but it was mainly involved in wine bitterness as a consequence of sensory interactions with other compounds (Cretin et al., 2018). The removal of ethanol leads to a loss of viscosity, body and fullness, and reinforces the aggressiveness of tannins (Jordão et al., 2015; Longo et al., 2017; Schmitt and Christmann, 2022). The complete elimination of ethanol, which can represent more than 20 % of the initial wine volume depending on the technology and the ethanol concentration of the distillate (Belisario-Sanchez et al., 2009), can also indirectly contribute by concentrating non-volatile molecules, such as organic acids or polyphenols.

Data on consumer assessment of ethanol or ethanol lowering in wine, including in partially dealcoholised wines, remains scarce. In an early review article, Pickering (2000) suggested that expected limitations in sensory quality, intrinsic tastes and an attitude of “snobbishness” towards such beverages might constitute barriers to consumer uptake. Experimental studies have shown that for consumers the appeal of wine and its expected quality usually decreased with lower ethanol content on the wine label (Masson and Aurier, 2008; Vasiljevic et al., 2018). While still preliminary, these findings were not consistent with the results of the tasting session, as wine with an ethanol content of 9 % v/v was not perceived differently to standard wine by consumers (Masson and Aurier, 2008). The same trend was also observed by Meillon et al. (2010) in the 10-14 % v/v ethanol range, even though consumer liking was less evident, suggesting strong segmentation.

The aim of this research work was to explore a wider range of ethanol lowering and to formally evaluate consumer response to ethanol in white and red wines using the consumer rejection threshold (CRT) method (Prescott et al., 2005). The CRT approach, which is based on the repetition of paired preference tests, has been previously applied to compounds responsible for wine faults, such as cork taint (Prescott et al., 2005) or 3-isobutyl-2-methoxypyrazine (Geffroy et al., 2020), and more generally to determine a level of concentration beyond which a given molecule becomes undesirable (Francis and Williamson, 2015; Geffroy et al., 2018). In both base wines, difference thresholds for ethanol were also defined during a preliminary experiment to determine the difference in ethanol concentration that can be perceived by consumers.

Materials and methods

Results and discussion

The distribution of the individual difference threshold concentrations according to the E 679 method is shown in Figure 1. The panel difference threshold was estimated at 1.31 and 1.36 % v/v for Chardonnay and Syrah respectively. For both wines, one participant succeeded at the lowest tested concentration, while one and three participants missed at the highest concentration for Chardonnay and Syrah respectively. While difference thresholds of up to 4 % v/v have been previously reported for ethanol (Hinreiner et al., 1955), our findings have the same range of concentrations as those found in a recent research based on ASTM E 679, which highlighted retronasal values ranging from 1.03 and 1.32 % v/v (Yu and Pickering, 2008). Our panel had little experience in wine assessment and was composed of Caucasian subjects. We can assume that our slightly higher thresholds might be related to panel differences in terms of experience, consumption frequency and ethnicity as proposed by Yu and Pickering (2008).

Figure 1. Distribution of difference thresholds for ethanol in Chardonnay and Syrah wines according to the ASTM E 679 method (n = 19 panelists). The panel threshold was estimated at 1.31 v/v and 1.36 % v/v for Chardonnay and Syrah respectively.

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For the ASTM E 1432 procedure, thresholds of 1.55 and 1.82 % v/v were established for Chardonnay and Syrah respectively (Figure 2). The fact that lower difference thresholds were obtained for the ASTM E 679 is in accordance with previous work aiming at comparing the two methods (Cliff et al., 2011).

Figure 2. Difference threshold determinations for ethanol in Chardonnay and Syrah wines according to the ASTM E 1432 method using a log-linear model at 50 % correct response above chance (n = 19 panelists). Model gave y = 0.2619 ln(x) + 0.3842, r² = 0.71 for Chardonnay; y = 0.3075 ln(x) + 0.321, r² = 0.94 for Syrah. The panel threshold was estimated at 1.55 % v/v and 1.82 % v/v for Chardonnay and Syrah respectively.

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Even though in agreement with previous observations (Yu and Pickering, 2008), the reason why a higher panel threshold - albeit non-significant according to ASTM E 679 and Mann-Whitney test (P = 0.404) - was observed for the red wine remains unclear. It can be hypothesised that its composition, in particular its tannin concentration, played a key role. It is well known that such macromolecules reduce the headspace concentration of volatile aroma compounds and their associated odour threshold values (Robinson et al., 2009; Villamor et al., 2013). We can assume that these phenolic compounds played a higher buffer role than in Chardonnay, and mitigated the perception of ethanol modification during the olfactory evaluation.

The ethanol concentrations to be assessed were chosen on the basis that ethanol lowering should start at detectable levels, corresponding to around 1.5 % v/v for both wines according to the previously described results. For both cultivars, the ethanol in the test samples was lowered by 1.5, 3.0, 6.0 and 12.0 % v/v; the Chardonnay test samples thus had a final ethanol content of 12.3, 10.8, 7.8 and 1.8 % v/v, while Syrah had 12.0, 10.5, 7.5 and 1.5 % v/v.

CRTs were calculated as being 2.8 and 7.0 % v/v for Chardonnay and Syrah respectively (Figure 3). These particularly low threshold values were somewhat unexpected, as they support the hypothesis that consumer sensory preferences are little driven by ethanol content, particularly in the case of white wine. However, the post-evaluation questionnaire revealed that panelists expected minimal and maximal ethanol contents for a quality wine of 10.9 % v/v ± 1.2 and 13.7 % v/v ± 1.2, and 11.7 % v/v ± 1.5 and 14.7 % v/v ± 1.0 for white and red wines respectively. Moreover, they claimed to: drink low ethanol wines very often (2.4 %), often (21.4 %), rarely (54.8 %) and never (21.4 %); drink dealcoholised wines often (2.5 %), rarely (2.5 %) and never (95.0 %); and consult the label for ethanol content at purchase always (9.5 %), often (38.1 %), rarely (28.6 %) and never (23.8 %).

Figure 3. Proportion of panelists preferring the control sample in A) Chardonnay and B) Syrah wines. Horizontal lines show that the “control is significantly preferred” at 5 % risk using paired comparison tests (n = 42 consumers). The consumer rejection threshold (CRT) was estimated at 2.8 % v/v and 7.0 % v/v for Chardonnay and Syrah respectively.

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These observations indicate that consumers have high ethanol expectations for quality wines, but have little experience with low ethanol or dealcoholised wines. However, they would not necessarily be refractory to the consumption of such beverages from a sensory standpoint. Therefore, professionals from the wine industry and public authorities should be strongly encouraged to raise awareness about the increase in quality of such products and their benefits for human health.

The non-parametric tests showed that the frequency of wine and dealcoholised wine consumption, together with the frequency of that the label was consulted for ethanol content at purchase, had a significant impact on consumer preferences (Table 1). The results of these statistical treatments must be considered with caution as subgroups might not always be representative samples. Those who claimed to rarely consult the label for ethanol content significantly preferred the test samples at 7.8 % v/v for Chardonnay and at 12.0 % v/v for Syrah, in comparison to those who often checked for ethanol content and preferred the control. This highlights that the latter participants have a certain amount of knowledge and a greater awareness of ethanol, and a better ability to perceive it in wine. For Chardonnay, consumers who drink wine every day significantly preferred the control samples at 11.8 and 7.8 % v/v. This could be explained by such subjects being likely familiar with usual ethanol contents, such as those found in the control samples. Consequently, their unfamiliarity with modified ethanol concentrations, which is in most cases negatively correlated with liking (Saliba et al., 2009), might have affected their assessment of the test samples. Unexpectedly, and contrary to what would have been expected based on a previous study (Meillon et al., 2010), the level of wine knowledge did not impact preferences. The fact that the preferences were not affected by age likely proves that no bias was introduced into our data by the larger proportion of young consumers included in our panel (28.6 %). Recalculations of CRT after randomly removing 6 consumers aged between 18 and 30 to obtain a perfect age balance within our panel, only lowered the concentrations to 2.6 and 6.9 % v/v for Chardonnay and Syrah respectively.

The difference in CRT concentrations between the two matrices indicates that the contribution of ethanol to the overall balance of red wine is higher. According to the terms used by consumers to describe the test samples (Table 2), the red samples reduced in ethanol to 7.5 and 1.5 % v/v were both significantly characterised by a higher aggressivity in comparison with Chardonnay samples; this is likely due to tannins, which is in accordance with previous findings (Jordão et al., 2015; Longo et al., 2017; Schmitt and Christmann, 2022). Similar to other studies, these wines were also perceived as being more diluted, less sweet and sourer (Fischer and Noble, 1994; Martin and Pangborn, 1970; Scinska et al., 2000). The fact that they were perceived as less intense in terms of aroma when a higher intensity would have been expected (Conner et al., 1998; Escudero et al., 2007) could be the consequence of the overall negative perception in the palate, which affects how aroma is perceived, and/or consumers being unable to describe their sensation. As expected, the Chardonnay wines at 7.8 and 1.8 % v/v were perceived as being more intense in terms of aroma, tasteless, more diluted and lighter in alcohol; however, the citation frequencies for these terms did not enable them to be discriminated from the Syrah samples.

It should be noted that our results are only valid for balanced wines made from Chardonnay and Syrah. The choice of unbalanced base wines could have led to distinct CRT concentrations notably lower CRT values for base wines characterised by excessive ethanol contents that cause intense burning sensations in the palate. On the other hand, it cannot be discarded that the use of base wines characterised by higher intensities of bitterness for Chardonnay and astringency for Syrah would have amplified the impact of ethanol reduction and led to higher CRTs. Our study is still preliminary, and more work would be needed to investigate the impact of the matrix more deeply by testing several wines made from the same grape variety.

In our study, we made the methodological choice of compensating for the loss in volume due to ethanol elimination by adding water. If permitted by the regulations, this could be of interest to wine producers, as it enables an economic valuation of ethanol without a reduction in volume of the alcoholic beverages. However, as reflected in the terms used to describe the Chardonnay test samples at 7.8 and 1.8 % v/v (Table 2), the addition of water might have enhanced the perception of dilution and lack of taste. It might also have contributed to obtaining lower CRT values by reducing the sensory perception of non-volatile compounds, such as organic acids and tannins that can enhance aggressiveness in reduced ethanol beverages (Jordão et al., 2015; Longo et al., 2017; Schmitt and Christmann, 2022).

Even if the SCC process, which limits aroma loss, has become the reference method for qualitative wine dealcoholisation (Pickering, 2000; Sam et al., 2021), and the sensory properties of the two control wines after reconstitution were similar to those of the base wines, the use of the two native wines without treatment as control samples might have led to different results. In a similar way, it cannot be excluded that the implementation of alternative techniques to SCC, such as reverse osmosis that has recently proved its sensory superiority (García et al., 2021), would have possibly affected CRT concentrations.

Conclusion

In accordance with previous findings, ethanol difference thresholds were estimated in this study to be around 1.5 % v/v in both matrices. The threshold ethanol concentrations at which ethanol becomes undesirable were determined to be 2.8 % v/v for Chardonnay and 7.0 % v/v for Syrah using the consumer rejection threshold approach (CRT).

These particularly low and somewhat unexpected concentrations indicate that ethanol content might not drive consumer sensory liking, especially in white wine. However, the post-evaluation questionnaire showed that consumers expected a high minimal ethanol content for quality wines, had limited experience with low and dealcoholised wines, and rarely or never consulted the wine label for ethanol content at purchase.

From a sensory standpoint, our data show that consumers might not necessarily be refractory to the consumption of beverages made from wine with a modified ethanol content; on this basis, wine industry professionals and public authorities can be strongly encouraged to raise awareness about the increase in quality of such products and their benefits for human health. Our findings are still preliminary, and more work would be necessary to validate them by studying a larger number of consumers. The impact of the matrix resulting from testing several wines made from the same grape variety should also be more deeply investigated.

Acknowledgements

We are grateful to the panelists from the Ecole d’Ingénieurs de Purpan and to all the consumers who participated in the study. We are also grateful to Fábio da Silva and Tim Birks (Flavourtech), Agnès Arquier (Dom Brial), and Alix Becheau, Victor Escat, Baptiste Maigne and Amandine Arnal (Ecole d’Ingénieurs de Purpan) for their technical support and assistance.

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