The Agricultural Research Council (ARC) and the Cap Classique Producers’ Association undertook a collaborative project to investigate a selection of bottle-fermented sparkling wines closed with corks and crown caps.
Introduction – cork or crown?
The use of crown caps during the production of bottle-fermented sparkling wine is a standard practice worldwide. Before the development of crown caps, bottles were closed with a cork held in place with a metal staple (agrafe).
The first crown caps were used commercially in the 1960’s.1 In South Africa, there are an estimated 250 producers of bottle-fermented sparkling wine (Méthode Cap Classique or MCC).2
In an ever-more competitive market, one of the tools that can be used to produce niche products is the use of a cork instead of a crown cap during the second fermentation.
Some international producers still follow this practice for the production of their premium products 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.3
Anecdotal observations made by some MCC producers are that the use of a cork leads to stylistic changes in the wines, such as smaller bubbles and an increase in wine complexity.
It has also been observed that this beneficial ‘cork effect’ becomes more noticeable the longer the wine on the lees is in contact with the cork.
In still wines it has been shown that compounds such as phenolics migrate from the cork to the wine at the cork-wine interface,4,5,6 but not much is known about sparkling wine where a two-disc cork is used.
This article is a summary of information found in a publication in the South African Journal of Enology and Viticulture, Volume 42.7
Materials and methods
Six treatment pairs of commercially prepared bottle-fermented sparkling wines were obtained for analyses from three South African producers (2012, 2013, 2015 and 2018 vintages).
These wines had been in contact with the yeast lees between four and 72 months. For each sparkling wine pair, the only differences between the wines were a cork or crown cap closure during fermentation and maturation on lees.
Wines used for chemical analyses had their lees intact, while wines for sensory analyses investigations were clarified by disgorging. The disgorged wines received no dosage.
Individual bottles served as replicates and the results were analysed statistically to ensure validity of the data.
Crown & cork: results and discussions
In this study each cork-crown wine pair originated from the same bottling tank with the only variable being a cork or crown cap closure for the second fermentation and aging on lees.
Consequently, individual cork-crown wine pairs could be compared and overall trends deduced across the various wine pairs.
A variation in bottle pressure within treatment replicates was observed, but overall, crown-capped wines tended to have higher pressures than their cork-closed counterparts.
The crown cap was therefore deemed a more effective barrier than the cork for maintaining bottle pressure.
Notwithstanding, the final pressure of the cork-closed wines were well above the legal minimum limit (>300 kPa) for the final products.
Analyses of infra-red spectral fingerprints generated by an Alpha spectrophotometer during standard wine analyses showed varying degrees of separation between the cork-closed and crown-capped wines for the oldest vintages, and less/none for the youngest vintages (as illustrated in Figure 1a and 1b).
This indicates a chemical difference in the wine matrix of the older wines and supports the MCC producer’s observations that longer periods of cork contact are required before a ‘cork effect’ is noticeable.
(a)
(b)
Differences in MCC cork-closed (green points) and crown-capped wines (blue points) for (a) 2012 (72 months on lees), and (b) 2018 (4 months on lees) vintages based on analysis of infra-red spectral data.
Further chemical analyses showed that total acidity, pH and malic acid content, largely determined during base wine preparation before bottling, were not affected by the closure and were the same for each cork-crown wine pair.
Yeast autolysis, generally regarded as a positive contributor to the sensory profile of bottle-fermented sparkling wines, also leads to an increase in mouthfeel (body) of wine and an increase in nitrogen levels.
Therefore, YAN (yeast assimilable nitrogen) and total extract measurements can serve as broad indicators of the progress of autolysis.
In the youngest wine (2018 vintage), which had only been on the lees for four months, it appeared that autolysis had started sooner in the cork-closed wine than in the crown-capped wine.
For the wines that were on the lees between 39 to 48 months, yeast autolysis was the same for the cork and crown wines and for the older wines (60 to 72 months on the lees), the data suggested that yeast autolysis was more advanced in the older crown-capped wines compared to their cork-closed counterparts.
One of the key compounds that could play a role in the perceived ‘cork effect’ in sparkling wines, is phenolic acids.
These acids contribute to wine sensory properties such as astringency and bitterness, as part of mouthfeel, structure and persistence of flavour.
Phenolic acids in wine are derived from grapes, but are also present in cork and can migrate into the wine at the wine-cork interface.4,5,6
These monomeric phenolics can polymerise to form complexes with other wine compounds.
It was therefore expected that the cork-closed wines would have higher levels of phenolic acids than the crown-capped wines, and that the older cork-closed wines would have higher levels than the younger cork-closed wines.
However, this was not substantiated by the data. Analyses of the individual phenolic acids also showed no consistent patterns among the levels of gallic, caftaric, caffeic and p-coumaric acids between cork-crown wine pairs.
However, gallic acid showed the most variation between cork and crown wines. Notwithstanding, these changes in phenolic acid profile could be detected within four months after bottling.
This implies that although anecdotal sensory effects may only be noticed after a number of years of cork contact, migration of phenolic acids occurred sooner than anticipated.
Phenolic acids can therefore be used as chemical markers to measure the ‘cork effect’ on wines.
The overall differences observed between the infra-red spectral fingerprints and the phenolic acid data of cork-closed and crown-capped wines were expected to be reflected in the sensory data. This was true for most of the wines.
The sensory differences between the cork-closed and crown-capped wines appeared to be more pronounced in the oldest wine (2012 vintage), and less so in the youngest wine (2015 vintage).
The 2018 wine was not sensorially evaluated as it had not been on the lees for the required number of months.
Overall, the cork-closed wines were generally associated visually with smaller bubbles, less pronounced autolytic character and a longer aftertaste, and for the older cork-closed wines, with yeasty and sometimes toasty attributes.
In contrast, the crown-capped wines were associated visually with larger bubbles, more pronounced autolytic character and a shorter aftertaste.
The more pronounced autolytic character could be the result of high levels of yeast autolysis, as previously noted.
None of the sparkling wines had any cork taint faults.
The smaller bubbles and longer aftertaste found in the cork-closed wines are desirable sensory characteristics and can lead to a perception that these wines are more complex in flavour than the crown-capped wines.
These measured sensory differences support the view held by MCC producers that a cork closure brings about a stylistic change to their wines.
Conclusion
Six pairs of wines from five vintages, closed by either a cork or crown cap, were investigated. Infra-red spectroscopy was shown to be a powerful and inexpensive tool to illustrate differences between the pairs of cork-crown wines.
Contact with the cork resulted in changes in the wine’s phenolic acid profile.
Gallic, caftaric, caffeic and p-coumaric acids can be used collectively as marker compounds to differentiate between cork- and crown-capped wines.
Furthermore, the use of corks brought about a sensorial change to the wines.
Cork-closed wines had visually smaller bubbles, less autolytic character, but had a longer aftertaste than the crown-capped wines.
The data generated in this study therefore tentatively supports the anecdotal observations made by sparkling wine producers regarding the ‘cork effect’ on MCC wines.
Therefore, producers wanting to change their style of wine can use cork as a wine production tool.
Abstract
A production tool that can be used for bottle-fermented sparkling wine is a cork closure instead of a crown cap during the second fermentation and maturation on yeast lees.
Anecdotal evidence suggests that this leads to stylistic changes in the wine.
In a collaborative project undertaken by the ARC and the Cap Classique Producers’ Association, six MCC wines, closed by either a cork or crown cap, were investigated.
It was found that cork-closed wines tended to have lower pressures, compared to crown-capped wines, albeit still well within legal requirements.
Other differences were evident in the infra-red spectral fingerprint and in the polyphenol profile of the wines.
Levels of gallic, caftaric, caffeic and p-coumaric acids could be used collectively as marker compounds to differentiate between cork-closed and crown-capped wines.
The effect of the cork was also evident in sensory attributes.
Cork-closed wines were judged to have smaller bubbles and a longer aftertaste.
The data generated tentatively supports the anecdotal evidence that a cork closure can be used during the second fermentation and maturation on the yeast lees to change the style of bottle-fermented sparkling wine.
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.
References
- Anonymous, 2020. From Vine to wine: effervescence – Three centuries of research. Comité interprofessionne du vin de Champagne. https://www.champagne.fr/en/from-vine-to-wine/what-is-champagne-wine/effervescence/effervescence-history. Accessed 30 November 2020.
- Anonymous, 2021. Cap Classique Producers’ Association. capclassique.co.za. Accessed 15 April 2021.
- Anonymous, 2021. Dom Perignon: Plénitude 2. domperignon.com. Accessed 15 April 2021.
- Varea, S., García-Vallejo, M., Cadahía, E. & de Simón, F.B., 2001. Polyphenols susceptible to migrate from cork stoppers to wine. Eur. Food Res. Technol. 213, 56-61.
- Azevedo, J. Fernandes, I., Lopes, P., Roseira, I., Cabral, M., Mateus, N. & Freita, V., 2014. Migration of phenolic compounds from different cork stoppers to wine model solutions: antioxidant and biological relevance. Eur. Food Res. Technol. 239, 951-960.
- Pinto, J., Oliveira, A.S., Lopes, P., Roseira, I., Cabral, M., de Lourdes-Bastos, M. & Guedes de Pinho, P., 2019. Characterisation of chemical compounds susceptible to be extracted from cork by the wine using GC-MS and 1H NMR metabolomics approaches. Food Chem. 271, 639-649.
- 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.
– For more information, contact Neil at jollyn@arc.agric.za.
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