Can Aroma Change the Astringency of Wine?

The “astringency” of red wine includes several sensations, such as a dry mouth, roughness, and smoothness. Are these determined solely by compounds such as tannins? Or can the aromas experienced alongside them change the impression too?

In 2020, Elisabetta Pittari and colleagues compared 74 Italian red wines with samples from which the aroma had been removed. They wanted to understand how aroma relates to sensations in the mouth, and whether the relationship between chemical composition and sensory ratings changes in the presence or absence of aroma. The study also concerned how far wine mouthfeel can be predicted from chemical analysis.

74 Red Wines and Their Corresponding Deodorized Samples

The study used 74 single-varietal red wines from 10 grape varieties, including Sangiovese, Nebbiolo, and Corvina. All were made in 2016 and sampled before malolactic fermentation or barrel aging. This was not a comparison of mature commercial wines in general.

The researchers removed aroma using a combination of low-temperature ultrasound treatment and evaporation under reduced pressure, then added water and food-grade ethanol to restore the original weight and alcohol content. They chose this treatment rather than nose clips so that participants could evaluate the wines under breathing conditions closer to normal tasting.

The assessors were 14 people aged 22–49 with experience in wine sensory evaluation: seven men and seven women. Using reference samples, they were trained in aroma descriptors, seven astringency attributes, and three taste attributes: sweetness, sourness, and bitterness.

The 74 original wines and 74 deodorized wines were each evaluated twice, giving a total of 296 sample assessments across 15 sessions. The samples were numbered, their identities were concealed from participants, and their presentation order was randomized. The figure 296 is the total number of sample assessments, not the number of different wines.

Removing Aroma Increased Bitterness and Some Aspects of Astringency

In the analysis of all 74 wines together, seven of the 10 oral attributes differed significantly between the aromatic and deodorized samples. Removing aroma increased some strong oral sensations, including harsh astringency, and bitterness, while reducing sweetness and velvety smoothness.

However, the result was not that “aroma weakens every aspect of astringency.” Drying, one of the characteristic sensations of astringency, particulate sensations, and sourness showed no significant differences overall. The involvement of aroma depended on which aspect of mouthfeel was being evaluated.

There were differences between grape varieties too. For example, in Corvina, which was characterized by green, vegetal aromas, deodorization reduced “unripe” astringency. In Nebbiolo, Sangiovese, and Aglianico, the same attribute increased after deodorization. Aroma did not necessarily act in a single direction.

The Terms “Unripe” and “Complex” Also Include Aroma

The definitions of the evaluation terms are important to understanding this study. The attribute corresponding to “complexity” described a harmonious combination of mild astringency, sourness, and retronasal aroma passing from the mouth to the nose. “Unripe” described a disharmonious combination of astringency, sourness, and green aroma.

Both are composite descriptions that include aroma from the outset, so the way the terms are constructed also matters when they change after aroma removal. They do not measure a single, purely tactile sensation. This is a limitation, but it also illustrates how everyday descriptions of wine bring several senses together in a single term.

Analysis of correlations between aroma types and oral sensations found weak but significant relationships between spicy aroma and complexity, dried-fruit aroma and drying, and vegetal aroma and the unripe sensation. Together with findings such as the Corvina result, these led the authors to consider whether impressions evoked by aroma might be involved in particular aspects of mouthfeel.

However, these results were not obtained by adding individual aroma compounds one at a time. Many compounds coexist in wine, and correlations alone cannot identify the cause. The authors also state that specific combinations of aroma and astringency need to be tested in further experiments.

Aroma Also Changes How the Relationship Between Composition and Mouthfeel Appears

The researchers also measured total phenols, proanthocyanidins, sugars, ethanol, acidity, and other parameters, and examined their relationships with sensory ratings. Proanthocyanidins are a group of tannins involved in wine astringency.

Overall, correlations between component levels and sensory ratings were often stronger in deodorized samples. The correlation between proanthocyanidins and drying reached around 0.70 after deodorization. The correlation between sugars and sweetness also rose from approximately 0.10 in the original wines to approximately 0.60 after deodorization.

This does not mean that removing aroma allows a wine’s “true taste” to be measured. In actual wine, we experience the combination of compounds in contact with the mouth and aroma. The authors’ point is that, even when investigating how well a compound predicts mouthfeel, its role can be harder to discern unless interactions with aroma are considered.

By contrast, after deodorization, the “unripe” sensation showed no significant correlation with polyphenol-related measurements. The authors interpret this sensation not as a scale corresponding solely to tannin quantity, but as a combination of several sensations, including sourness and aroma.

Comparing Wines After Deodorization Has Limitations Too

The effectiveness of deodorization was checked by instrumental analysis, and no significant visual differences were detected in a subset of samples. Based on the low processing temperatures and previous research, the researchers considered the resulting samples representative of the original wines.

Even so, given that ultrasound treatment, evaporation, and reconstitution were performed, it cannot be stated with certainty that every property other than aroma remained exactly the same. Comparison with methods such as blocking the nose is also identified as a future task. In addition, these evaluations were made by 14 trained assessors, not a direct investigation of ordinary wine drinkers’ preferences or purchasing behavior.

Summary

Red wine astringency has several aspects, including drying and smoothness. In this study, removing aroma changed some of these aspects, as well as sweetness and bitterness, and the direction of change differed between attributes and wines.

Aroma was involved not only in mouthfeel ratings but also in the relationships used to predict sensations from component levels. The authors’ findings suggest that understanding red wine quality is helped by going beyond a single scale of astringency intensity, distinguishing which sensation is meant, and examining how that sensation combines with aroma.

References

Pittari, E., Moio, L., Arapitsas, P., Curioni, A., Gerbi, V., Parpinello, G. P., Ugliano, M., & Piombino, P. (2020). Exploring Olfactory–Oral Cross-Modal Interactions through Sensory and Chemical Characteristics of Italian Red Wines. Foods, 9(11), 1530. DOI: 10.3390/foods9111530 · Full original article.

Original article: © 2020 the authors. Licensee MDPI, Basel, Switzerland. CC BY 4.0. The research was partly supported by Italy’s MIUR through a PRIN 2015 grant. The authors declare no conflicts of interest.