Winetech Technical Yearbook 2022

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FIGURE 1. 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. Each point represents an individual bottle.

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 per ceived ‘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 spec tral 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 sen sorially 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 autolyt ic 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 af tertaste. 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. (a) (b) FIGURE 1. Differences in MCC cork-closed (green po t ) nd crown- apped wines (blue points) for (a) 2012 (72 months on le s), and (b) 2018 (4 months on lees) vintages based on analysis of infra-red spectral data. Each point represents an individual bottle. 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 sa e for each c rk-crown wine pair. Yeast autolysis, gener lly 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 (ye st assim lable 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 m ths, it ppeared that autolysis had started o ner i the cork-closed wine than in the crown-capped wine. For the wines that were on the lees between 39 to 48 months, yeast a toly is was the sam for the cork d cr wn 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 s nsory properties such as astringency and bitterness, as pa t of mouthfeel, structure and persistence of flavour. Phenolic acids in wine are derived from grapes, but are also present in cork and can migr t i to th wine at the wine-cork interface. 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 tha the crown capped wines, and th the older cork-cl sed wines would have higher levels than the CONCLUSIONS 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 https://www.wineland.co.za/cork-crown-closures-bottle fermentation/ For more information, contact Neil Jolly at jollyn@arc.agric.za.

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WINETECH TECHNICAL YEARBOOK 2022