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.

2 Responses to “Winemakers may be able to select cork according to its phenolic content”

  1. Lots of “mays” and “mights” makes this sound a bit more like the cork industry trying to hang on to a dying business, than any real breakthrough or discovery. The crack about screw tops creating volatile sulfur components during reductive aging (it is more likely from reductive wine making) is a prime example. The formation of tertiary aromas, esterfication and polymerization, also known as bottle aging, is reductive, period.

    That the subject is fully aware of this is demonstrated at the end of the article when he vacillates by saying that a little O2 comes from the cork but other than that pointing out that cork is not permeable – meaning it is going to also create a reductive environment for aging, just like a screw cap. In fact, with gas permeable liners screw caps can regulate just how reductive that aging process is, a practice I am not a fan of but is none the less an example of the cork industry trying too hard to find disadvantages to screw caps since the one they tout it is actually more applicable to their product, cork.

  2. Ross Farrell says:

    Whatever you believe regarding the science, I will always prefer natural cork closure for the wine I purchase, period. Cork is a natural, renewable material harvested from sustainably manged Quercus suber forests. These forests are vital to the health of such fragile arid ecosystems – visit the alentejo region & see the damage done by monocultures of short rotation plantation eucalypts. The cork “industry” therefore plays a role in the sustainability of our planet. Beyond that, the experience of removing the cork from a bottle of wine is for some a meditative, perhaps even spiritual experience. Natural materials play a role in our psychological well being – the Japanese have long believed that our homes should be made from natural wood products rather than synthetic alternatives – wood makes you feel good. It connects you to the planet. When I choose wine with a real cork, i’m making a choice for what I value, an appreciation for natural beauty and sustainability.

    Previously, cork suffered from some incidence of TCA, however the industry should be commended for its pursuit of a technological solution to assure this does not occur – by assessing every cork for the presence of part per trillion molecules of TCA & therefore guaranteeing TCA free cork. So you now have the tradition of cork backed by state of the art analytical technology. Cork is not a thing of the past nor an obsolete industry, it should be the bottle closure of choice for both performance and environmental reasons.

    Ross Farrell
    Wood Scientist
    Analytical Chemist
    Wine aficionado

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