Earlier this year, I covered an article looking at the influence of alcohol content on aroma (esters) release in wine tasting. I’m sort of following up on that post with a new study by the same authors taking the concept a little bit further.
In that article, the researchers found that overall, alcohol influences the release of aromas retronasally when tasting wine, at least for the majority of the 6 esters tested. Additionally, that study found that individual variation was much more significant for aroma release than the alcohol content itself.
Of course, wine is a bit more complex than just esters and alcohol alone, so further study is needed to get a better understanding of oral aroma release.
Studies, including the one I covered earlier this year, consistently show that alcohol content affects aroma release of many different aromatic esters in wine. What’s not as consistent, however, is the research regarding the effects of polyphenols on aroma release. As I mentioned, wine isn’t just alcohol and esters alone. Polyphenols are another group of compounds that make up a significant part of wine – best known for the antioxidant properties and often touted for their health benefits, polyphenols in wine include resveratrol, quercetin, anthocyanins, ellagic acid, et cetera.
Some studies have found that more polyphenols in wine might decrease oral aroma release of esters, which other studies did not find any sort of relationship. Considering there are many different types of polyphenols with different structures and in different concentrations depending upon the wine, these inconsistencies are not surprising.
According to the study authors, there has not been any published research to date that examined the effects of the more complex wine matrix (i.e. alcohol, esters, and polyphenols) on aroma release in wine, thus the study I present to you today (available online currently and to be printed in the September 2020 issue of Food Research International) was born.
Brief Methods
In order to study the effects of the more complex wine matrix on oral aroma release, the following methods were performed.
The control wine used in this study was a dealcoholized Tempranillo rosé with an ethanol content of 0.5% v/v.
Three treatment wines were created from this control wine with varying ethanol and polyphenol content to yield the following test wines:
- Low alcohol/Low polyphenols (control wine: 0.5% abv, no added polyphenols)
- Low alcohol/Moderate polyphenols (0.5% abv, added polyphenols ~661mg gallic acid/L)
- Moderate alcohol/Low polyphenols (10% abv, no added polyphenols)
- Moderate alcohol/Moderate polyphenols (10% abv, added polyphenols ~661mg gallic acid/L)
Moderate alcohol wines were created by adding appropriate levels of food-grade ethanol.
The source of added polyphenols was the commercially-available tannin extract known as Vitaflavan.
Polyphenol level in the low polyphenol wines was found to be 402mg gallic acid/L, compared with the 661mg gallic acid/L in the wines with the added polyphenols.
Six food-grade esters were added to all wines to a final concentration of 4mg/L.
9 panelists (4 men, 5 women) performed tastings where they rinsed their mouths with each control and treatment wine, then spit off the wine and subsequent aroma released into their oral cavities was analyzed using fancy fibers and gas chromatography-mass spectrometry (GC-MS machines). To spare you the details, I implore you to read how they performed the test here in this other study. If you need other details, just let me know.
The following measurements were taken:
- Ester content of the wines that were spat off after rinsing.
- Ester persistence in the oral cavity immediately after spitting (“immediate oral release”)
- Ester persistence in the oral cavity 2 minutes after spitting (“prolonged oral ester release”)
- Note: if you read the methods of the previous study, their timing for “immediate” and “prolonged” oral ester release was slightly different than in this study).
Selected Results
Analysis of Spat-off Wines:
- The effects of panelists and the interactions with the wine matrix were significant.
- This suggests that the effects of wine matrix composition on oral release and retention of aromas (i.e. esters) depended upon who was tasting the wines (individual-dependent).
- Even with individual variation, wine matrix composition alone did also have an effect on oral release and retention of aromas.
- Four esters were significantly influenced by wine matrix composition (ethyl butyrate, ethyl hexanoate, ethyl octanoate, and ethyl decanoate), while two esters were not (isoamyl acetate and ethyl pentanoate).
- Ethanol concentration played a more important role in recovering esters in the spat-out wine than polyphenol concentration.
- Ethyl butyrate (more polar, volatile) was found significantly less in the spat-out wines with moderate alcohol levels compared to control wines. This suggests its presence might be higher in the oral cavity since it was not found as much in the spat-out wine.
- Esters with intermediate polarity and volatility (isoamyl acetate and ethyl pentanoate) were not affected by wine matrix composition in the spat-out wine.
- As hydrophobicity increased and volatility decreased, these types of esters (ethyl hexanoate, ethyl octanoate, ethyl decanoate) were more likely to be found in the spat-off wines with moderate alcohol levels compared with low alcohol levels. This suggests these compounds may not be held as well in the oral cavity as alcohol level increases.
Analysis of Oral Persistence of Esters:
- Ester persistence varied from 1% to 57%, as was a function of chain length.
- Esters that were more polar and volatile (ethyl butyrate, isoamyl acetate, ethyl pentanoate) had lower oral persistence than more apolar and less volatile esters (ethyl octanoate, ethyl decanoate).
- Wines with higher polyphenol content in the absence
of alcohol resulted in increased oral persistence of more apolar and less
volatile esters.
- Ethyl butanoate was LESS persistent with low alcohol/moderate polyphenol wines.
- Isoamyl acetate was not significantly influenced by the wine matrix.
- The wine with the moderate alcohol level and no
added polyphenols showed a significant increase in all esters tested in regards
to their oral persistence.
- This indicates the presence of alcohol likely increases the perception of fruity aromas in wines.
- The wine with the moderate alcohol level and the
moderate level of added polyphenols showed the most different results compared
with the control and all other wines studied.
- Ethyl butanoate was more persistent in the oral cavity after rinsing with this wine.
- Isoamyl acetate, ethyl hexanoate, ethyl octanoate were less persistent after rinsing with this wine.
- Ethyl pentanoate and ethyl decanoate were not influenced by the moderate/moderate wine matrix compared with the control.
Conclusions
This study, according to the authors, is the first time in the published literature where the influence of the complex wine matrix on oral release and persistence of aromatic esters was observed and analyzed.
Overall, the study showed that ethanol content influenced oral release and persistence of 6 esters. Additionally, the presence of added polyphenols also influenced this same phenomenon. Finally, there were interactions between the two seen, indicating that it was not one or the other that contributed to aroma release and retention in the mouth after rinsing and spitting. Specifically, moderate levels of added polyphenols in the low alcohol wine (nearly alcohol-free at 0.5% abv) increased the persistence of esters in the mouth, which would theoretically lend itself to fruitier-tasting wines (or at least perceived fruitiness). Additionally, the moderate alcohol wines with lower polyphenols also increased ester release in persistence in the mouth.
Interestingly, the wine with both moderate levels of alcohol and moderate levels of added polyphenols actually DECREASED oral ester persistence, indicating that there may be interactions between the two at certain levels that might decrease perceived fruitiness and aroma persistence in the mouth.
To make matters even more complicated, oral release and persistence of esters also depended upon the ester itself and the physicochemical properties of the individual ester compounds. AND this release is also dependent upon the individual person tasting the wine.
To summarize something pretty complicated in one sentence: oral ester release is dependent upon the physiochemical structure and nature of the ester as well as the composition of the wine matrix and the individual tasting the wine. In other words, it’s complicated, but at least now more information has been added to our wealth of knowledge on the subject, even if it just brings up more questions (which it should! Yay science!).
It’d be interesting to see this study expanded upon—more wines, more esters, different combinations of alcohol/polyphenol levels, larger participant pool, et cetera. Fun stuff!
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