Effect of cork or crown cap closures on MCC bubbles

A collaborative study was undertaken between the Cap Classique Producers’ Association and the ARC to investigate differences between cork-closed and crown-capped wines.

Sparkling wine is characterised by CO₂ content and the bubbles are the ‘sparkle’ that distinguishes sparkling wines from still wines.

This is the characteristic that consumers generally find appealing. The bubbles also add to the typical mouthfeel imparted by the release of dissolved CO₂ in the mouth.

During production, bottle-fermented sparkling wine undergoes a second alcoholic fermentation in the same bottle it is sold in.

It is a standard practise to use a crown cap to close this bottle. After the legislated period of maturation on the yeast lees, the wine is clarified and the crown cap is removed.

The bottle is then resealed with the customary two-disk cork kept in place by a wire hood (muselet). Before the development of crown caps in the 1960s,¹ a cork, secured with a metal staple, was used during the second fermentation.

Some international producers never changed from this protocol and still use cork for the second fermentation of their premium wines, despite the risk of cork taint.

For example, the Champagne Dom Perignon Plénitude can be in contact with a cork while on the yeast lees for up to 15 years before being released.²

One of the reasons for the use of a cork is a desired stylistic effect imparted to the wine.

Méthode Cap Classique (MCC) producers have noted that the use of a cork closure during the second fermentation delivers a desired smaller bubble and lengthens the time that the bubbles remain in the glass.

Part of this project investigated the CO₂ kinetics (the behaviour of bubbles or CO₂) after a glass of MCC wine had been poured.

This article is a summary of information presented in a publication in the South African Journal of Enology and Viticulture, Volume 42.³

Cork materials and methods

Six treatment pairs of commercially prepared bottle-fermented sparkling wines, covering the 2012, 2013, 2014, 2015 and 2018 vintages, were obtained for analyses from three MCC producers.

These wines had been in contact with the yeast lees between four and 72 months at time of analyses.

For each sparkling wine pair, the only differences between the wines were a cork or crown cap closure during fermentation and maturation on lees.

Before analyses, the wines were disgorged by the respective cellars and all were reclosed with a crown cap.

A method was adapted to measure the amount of CO₂ lost from an ISO wine tasting glass (CO₂ mass loss), and the change in the number of visible bubbles in a flute glass over 20 minutes (bubble count).

The counting method did not distinguish between small and large bubble sizes and individual bottles served as replicates.

Results and discussions

In this investigation, 20 minutes was considered a reasonable time elapse from pouring a glass of MCC wine to consumption in a social setting.

However, many consumers would probably finish their glass in a shorter time.

The quantity of CO₂ that could potentially be lost from a glass depends on the quantity initially present in the bottle i.e., the bottle pressure.

Wines at high pressures lose CO₂ faster than those at low pressures to attain a gas equilibrium between the wine and the headspace of the glass.

Additionally, the turbulence caused during pouring, results in a notable further loss of dissolved CO₂, especially for the first glass poured.⁴

Generally, the crown-capped wines had higher pressures compared to the cork wines. It was therefore expected that the crown-capped wines would lose more CO₂ than the cork-closed wines.

This was true for four of the six wines, but only statistically significant for one of the four wine pairs (Figure 1).

The remaining two wines, both from the same producer, showed the converse and more CO₂ was lost from the cork wines which was not in agreement with the initial pressure readings.

These discrepancies may be due to the pressure readings and mass loss kinetics measurements been taken on different bottles.

However, the average trend across all treatments showed that the cork wines retained their CO₂ content marginally better than the crown-capped wines after pouring.

FIGURE 1. Total CO₂ mass loss from an ISO standard tasting glass of six pairs of Méthode Cap Classique sparkling wine after 20 minutes

The second part of the CO₂ kinetic evaluation determined bubble counts in four of the six sets of wine using photographic images of glasses of wine.

The initial average count (time zero) over all treatments varied greatly, but was slightly higher for the cork-closed wine (881 ± 488 bubbles/image) than the crown-capped wine (826 ± 197 bubbles/image).

The use of a single flute glass for all the measurements eliminated bubble nucleation sites as a variable, therefore, the observed differences can be ascribed to intrinsic wine characteristics.

The number of bubbles counted per individual glass decreased exponentially over 20 minutes, which was similar to the trend observed for mass loss.

Expressing the bubble count as a percentage of the number initially present in the glass, showed that after 10 minutes in the glass, cork-closed wines generally had higher bubble counts than crown-capped wines (Figure 2).

However, this was not sustained and after 20 minutes, the cork-closed and crown-capped wines had, on average, similar bubble counts.

Individually, two wines had notable higher bubble counts after 10 and 20 minutes for the cork-closed wine, compared to their crown-capped counterpart wine.

The remaining wine pairs either showed conversely more bubbles in the crown-capped wine or no differences between the two closure types.

A tentative conclusion can therefore be made that the closure type does affect the number of bubbles visible in the glass and, in some instances, a cork-closure was more amenable to retaining the appearance of bubbles in a glass of wine for the first 10 minutes after pouring.

% remaining bubbles in a flute glass of Cap Classique from four pairs of cork-closed (blue) and crown-capped (orange)  (a) 10 minutes, and (b) 20 minutes after pouring. 

The CO₂ content of a sparkling wine has been proposed to affect the aroma.

Droplets originating from bursting bubbles at the surface of the wine can release aromatic compounds into the immediate atmosphere in the glass.^5,6

This would have a direct effect on how a judge or consumer perceives the wine.

The higher the concentration of dissolved CO₂ in the wine, the faster the bubble formation, the larger the bubble size and higher the number of bubbles that can be released from the wine (effervescence).⁶

Therefore, the release of aroma compounds out of the glass will also be faster and could be lost to the atmosphere.

In this study, the cork wines tended to have lower pressure and dissolved CO₂ than the crown-capped wines, which based on the aforementioned discussion, should lead to slower bubble formation, smaller bubble size and slower release of bubbles and aroma components from the wine glass.

This would increase the perceived aroma in the glass. These observations also correlate with the higher number of bubbles counted.

The differences in wine pressure could therefore be one of the underlying reasons why the MCC producers observe that cork-closed wines have better foam stability and bubble retention time than crown-capped wines.

Conclusions

Six pairs of wines from five vintages, closed by either a cork or crown cap, were investigated. An effect on the CO₂ kinetics was observed after the wines were poured.

Cork-closed wines lost CO₂ slower than the crown-capped wines and had visually more bubbles. Based on the data generated in this study, anecdotal observations by MCC producers on the effect of cork on foam stability and bubble texture is tentatively supported.

Abstract

Carbon dioxide (CO₂) content is essential for the bubbles in sparkling wine.

Anecdotal evidence suggests that CO₂ kinetics (behaviour of the bubbles) in the wine glass can be affected if a cork closure is used during production instead of the customary crown cap.

In a collaborative project undertaken by the ARC and the Cap Classique Producers’ Association, six pairs of MCC wines, closed by either a cork or crown cap during production, were investigated.

It was found that the cork-closed wines tended to lose CO₂ slower from the glass after being poured than their crown-capped counterparts.

Bubble counts in the cork-closed wines were higher than the crown-capped wines for the first 10 minutes after pouring.

The data generated tentatively supports the anecdotal evidence that cork usage during the second fermentation and maturation on the yeast lees has a positive effect on the CO₂ kinetics.

Acknowledgements

Le Lude Cap Classique, Graham Beck Wines and Anthonij Rupert Wyne for donating wines and the Cap Classique Producers’ Association for initiating this investigation.

ARC Infruitec-Nietvoorbij and Winetech for funding. Pieter Ferreira and Paul Gerber for assistance and technical expertise.

Prof Gerard Liger-Belair and Dr Clara Cilindre, University of Reims, Reims, France, for sharing their expertise and protocols.

Denis Bunner, Champagne Bollinger, for sharing his expertise on Champagne.

References

1. Comité Champagne, 2020. From vine to wine: What is Champagne wine? Effervescence. Available here (accessed 30 November 2020).
2. Anonymous, 2021. Dom Perignon: Plénitude 2. www.domperignon.com. Accessed 15 April 2021
3. Jolly, N., Gerber, P., Minnaar, P., Booyse, M. 2021. Bottle Fermented Sparkling Wine: Cork or Crown Closures during the Second Fermentation? S. Afr. J. Enol. Vitic. 42, 136-153.
4. Liger-Belair, G., Parmentier, M. & Cilindre, C., 2012. More on the losses of dissolved CO₂ during Champagne serving: toward a multiparameter modelling. J. Agric. Food Chem. 60, 11777-11786.
5. Liger-Belair, G., Lemaresquier, H., Robillard, B., Duteurtre, B. & Jeandet, P., 2001. The secrets of fizz in Champagne wines: a phenomenological study. Am. J. Enol. Vitic. 52, 88-92.
6. Liger-Belair, G., Villaume, S., Cilindre, C. & Jeandet, P., 2009. Kinetics of CO₂ fluxes outgassing from Champagne glasses in tasting conditions: the role of temperature. J. Agric. Food Chem. 57, 1997-2003.

– For more information, contact Neil at jollyn@arc.agric.za.

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