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Winemakers may be able to select cork according to its phenolic content

In the future, winemakers may be able to select a natural cork closure with a specific concentration of phenolics to positively influence a wine’s development in the bottle.

Natural cork
Natural corks, which are punched from the bark of the cork oak, contain extractible phenolic compounds that may benefit the evolution of a wine once it has been bottled

As previously reported by the drinks business, cork may benefit the ageing of wine through the release of phenolics and volatiles from the structure of the closure, which comes from the bark of the Quercus suber, commonly called the cork oak.

In February last year, Dr. Miguel Cabral, who is director of R&D at Amorim, the world’s largest producer of cork closures, said that cork will release phenolic compounds in a “linear way” that react with the wine to form “new compounds”.

However, following further research, Cabral told the drinks business in Portugal last month that his studies on the phenolic composition of cork have shown that there is a structural fraction and extractible fraction in the closure, and that the latter contains 6% phenolic compounds, which can, for example, over time turn a colourless spirit such as vodka yellow.

So far, Cabral has identified 40 different extractible compounds in a natural cork, which, he said, may be beneficial to the ageing of wine.

“A cork in a bottle will release slow amounts of compounds into a wine that will react with the wine and produce complex compounds that probably have a role in colour stabilization and reducing bitterness and other roles we don’t know,” he told db.

Continuing he said, “You put wine in a barrel because you want these phenolics, and when you put wine in a bottle, it does receive some phenolics from the cork – date collected over 36 months shows that the cork will release a small amount of phenolics, and this is a linear release.”

Notably, Cabral said that these cork-derived phenolics “allow for a balanced wine ageing”, which, he said, was in contrast to other closures, commenting that “synethics [closures] accelerate ageing,” while the almost hermetic seal formed by a Saratin screwcap, which is tin-lined, “accelerates a reductive wine ageing” – referring to the production of volatile sulphur compounds that, it is believed, are formed as a wine ages in bottle without sufficient oxygen.

“So the positive of cork is balanced wine ageing,” he stated, pointing out that, for example, Dom Pérignon chooses to use cork, rather than crown cap for its Champagnes which are destined for extended cellaring in the brand’s Oenoteque.

Harvesting cork
Harvesting bark for making cork stoppers from the cork oak, Quercus suber

And the next stage for Cabral is to see if he can select a cork for its higher phenolic content, so it can be used for wines destined for extended ageing in bottle.

“Phenolics are variable in cork, and some corks release more than others, so our idea is trying to get a technique that will determine the amount of phenolics in the corks using infra-red technology,” he said.

Such an approach is already used by barrel manufacturers, observed Cabral, who said that a cooper such as Radoux is using Near Infrared Spectrometry to grade oak staves according to the phenolics, specifically tannins, that will be released into the wine.

“Our objective is that in the future, a wine producer could specify a cork with a high concentration of phenolics,” he said.

As for the role of oxygen in a wine’s development, he said that cork’s unique properties also benefitted this aspect to ageing wine.

“There is an initial bit of oxygen released into the wine from a cork in the first 6-8 months that comes from within the cork; it is expelled into the wine when the cork is inserted into the bottle, but the cork is not permeable, the oxygen’s origin is from the interior of the cork.

“And this initial bit of oxygen is not damaging the wine, and later on [in the wine’s development], it may facilitate oxidative reactions,” he said.

Finally, he said that a move to grading cork according to its phenolic content would help remove variability in the naturally-sourced closure.

Further analysis including views from manufacturers of synthetic closures and screwcaps will appear in the August edition of the drinks business, which features an article on the role of stoppers in a wine’s evolution.

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