Dr. Carien Coetzee
Basic Wine
11 August 2020
The concentration of dissolved carbon dioxide (CO2) can have a major influence on the sensory perception of wine. Attributes commonly associated with CO2 in beverages include “tingling”, “prickling”, “burning”, “fizzy” and “spritzy” and it is well known that too low CO2 concentrations will result in a wine tasting “flat” and lacking freshness. Typically, dissolved CO2 concentrations in Sauvignon Blanc wines will range anything from 0.8 g/L to 1.8 g/L, however, the exact CO2 sweet spot will depend on the wine style.
The concentration of dissolved CO2 can be adjusted by the winemaker to obtain the desired sensory effect. It can be lowered by sparging the wine with nitrogen gas while carbonation will increase the dissolved CO2 concentration. There are various recommendations1,2 when sparging which will be addressed in future blog posts.
Many opinions on the effect of dissolved CO2 on the perception of wines exist and researchers from The Australian Wine Research Institute conducted a formal study to elucidate the exact effects of which the results were published in a paper titled, “Effect of dissolved carbon dioxide on the sensory properties of still white and red wines”3.
Materials and methods
Two white and two red wines were used in the study3: Chardonnay (W1), Viognier (W2), Shiraz (R1) and Cabernet Sauvignon (R2).
In order to determine the effect of different CO2 concentrations on the sensory experience of the wines, the CO2 contents of the wines were adjusted to different levels (Table 1). Different CO2 levels were obtained by either blending the control wine with the same wine saturated with CO2 (increase) or with the same wine which had been entirely decarbonated by sparging with nitrogen (decrease). The white wines’ pH values were standardised after carbonation. No pH adjustments were needed for the red wines. After resealing the bottles, the wines were stored at 4°C for up to 48 hours prior to sensory assessment. The temperature of the white wines at the time of the sensory assessment was approximately 10°C, while the red wines were evaluated at approximately 23°C.
Table 1. The average concentration of dissolved CO2 in the white and red wine treatments after CO2 adjustments3
RESULTS
Loss of CO2 from bottle to glass
A preliminary test was conducted to investigate the change in dissolved CO2 concentration when the wine is poured from the bottle to the glass.
Results showed that there is a significant loss in CO2 during this process. The pouring of the wine from the bottle into the glass led to dissolved CO2 decreases of up to approximately 0.5 g/L. For the 20-minute duration after pouring, the dissolved CO2 concentration in the wine continued to decrease slowly and resulted in the decrease of an additional (approximately and up to) 0.5 g/L dissolved CO2. There were also differences in dissolved CO2 concentration of poured wine (in different glasses) from the same bottle. This in-glass variation is likely caused by differences in the amount of agitation while pouring. These losses and differences can be significant and should be considered when conducting sensory evaluations. The sensory assessment of the current study was conducted within two minutes after pouring the wine to minimise the loss of dissolved CO2.
The effect of dissolved CO2 on various sensory attributes
- As expected, the intensities of the attribute “spritz” were significantly higher in the treatments that contained higher concentrations of dissolved CO2 for both the white and red wines. The spritz sensation can thus be adjusted within the legally defined and commercially accepted concentration ranges for still wines.
- A significant increase in the intensity of “sweetness” was observed for the W1 treatments containing medium-high to high concentrations of dissolved CO2 when compared to the untreated control sample and the sparged wine (low). For W2, a similar increase in perceived sweetness was observed, however, the differences were marginal.
The dissolved CO2 similarly affected the red wines and the samples containing the highest concentration of CO2 (high) was perceived as being significantly sweeter compared to samples containing the lowest concentration of dissolved CO2 (low).
- For the two white wines tested, the intensity of “bitterness” decreased as dissolved CO2 increased. The perceived bitterness for both red wines also tended to be less intense when the dissolved CO2 concentration was higher, although this trend was not significant.
- The intensity of “astringency” decreased as the dissolved CO2 increased. This was mostly seen for W1, however, there seems to be a similar trend for the two red wines.
- For all four wines tested, the intensity of “overall fruit flavour” was lower (to varying degrees and significance) in the samples that were sparged with nitrogen (low) when compared to the other dissolved CO2. No change in attribute intensity was observed by increasing the dissolved CO2 compared to the control sample. The lower intensity of “overall fruit flavour” in the low samples could indicate that the delivery of odorants to the olfactory epithelium was handicapped due to the lack of dissolved CO24,5.
- Interestingly, the perception of “acidity” was not significantly affected by the dissolved CO2 concentration of the samples. Keep in mind the pH values of the white wines were standardised after carbonation. An increase in perceived acidity is often observed in carbonated water and is likely due to the formation of carbonic acid species under normal atmospheric conditions producing a slightly acidic solution (pH 5.7)6. In a more wine-like system, such as an aqueous solution containing organic acids, dissolved CO2 either had no effect7 or it suppressed perceived acidity8,9. This effect may be explained by the predominance (>98%) of CO2 over carbonic acid at wine pH6.
- Dissolved CO2 did not affect perceived viscosity of any of the wines.
Conclusion
The results reported in this study3 shows that the concentration of dissolved CO2 can significantly and directly affect the sensory perception of both white and red wines. The increase in perceived sweetness and the decrease in perceived bitterness due to higher dissolved CO2 concentrations in wine could change the way we look at carbonation/sparging especially for still wines which contain sub-saturated levels of dissolved CO2.
Some of these results differ when compared to similar studies conducted in CO2 saturated samples. Keep in mind that this study was performed to investigate the effect of dissolved CO2 on still wines (lower dissolved CO2 range), and not sparkling wines (saturated dissolved CO2).
The sensory interactive effects and the way the tasters perceive the wine as a whole should also be considered. For example, if a beverage tastes sweeter, it tends to also taste less bitter. However, the physiological mechanisms underlying dissolved CO2 induced reduction in bitterness and increase in sweetness still needs further investigation3.
DISCLAIMER
Some contradicting results were reported in the study3. I decided to rely on the interpretation of the results by the authors (as specified in the text) and assumed an error in one of the figures.
References
(1) Walls, J. R., Coetzee, C., du Toit, W. Factors Affecting the Efficacy of Sparging in South African White Wines. South African Soc. Enol. Vitic. WINETECH 41st Int. Conf. 2018, Poster.
(2) Walls, J. . Effect of Oxygen Management on White Wine Composition, Stellenbosch University, 2020.
(3) Gawel, R., Schulkin, A., Smith, P. A., Espinase, D., McRae, J. M. Effect of Dissolved Carbon Dioxide on the Sensory Properties of Still White and Red Wines. Aust. J. Grape Wine Res. 2020, 26 (2), 172–179.
(4) Pozo-Bayón, M. Á., Santos, M., Martín-Álvarez, P. J., Reineccius, G. Influence of Carbonation on Aroma Release from Liquid Systems Using an Artificial Throat and a Proton Transfer Reaction-Mass Spectrometric Technique (PTR-MS). Flavour Fragr. J. 2009, 24 (5), 226–233.
(5) Saint-Eve, A., Déléris, I., Aubin, E., Semon, E., Feron, G., Rabillier, J.-M., Ibarra, D., Guichard, E., Souchon, I. Influence of Composition (CO2 and Sugar) on Aroma Release and Perception of Mint-Flavored Carbonated Beverages. J. Agric. Food Chem. 2009, 57 (13), 5891–5898.
(6) Chaix, E., Guillaume, C., Guillard, V. Oxygen and Carbon Dioxide Solubility and Diffusivity in Solid Food Matrices: A Review of Past and Current Knowledge. Compr. Rev. Food Sci. Food Saf. 2014, 13 (3), 261–286.
(7) Hewson, L., Hollowood, T., Chandra, S., Hort, J. Gustatory, Olfactory and Trigeminal Interactions in a Model Carbonated Beverage. Chemosens. Percept. 2009, 2 (2), 94–107.
(8) Cometto-Muñiz, J. E., García-Medina, M. R., Calviño, A. M., Noriega, G. Interactions between CO2 Oral Pungency and Taste. Perception 1987, 16 (5), 629–640.
(9) Symoneaux, R., Le Quéré, J. M., Baron, A., Bauduin, R., Chollet, S. Impact of CO2 and Its Interaction with the Matrix Components on Sensory Perception in Model Cider. LWT – Food Sci. Technol. 2015, 63 (2), 886–891.
Photo by Gerard Richard on Unsplash
