Cork Or Plastic? The Science Of Stopping Your Wine

May 5th, 2022
Cork Or Plastic? The Science Of Stopping Your Wine

Sometimes it really is the little things. It shouldn’t matter so much - but what would opening a bottle of wine be without that first “pop!” as the cork comes out, both comical & sophisticated, and always immensely satisfying?

It’s a problem wine-makers have been wrestling with for decades, ever since the arrival of cork alternatives. Who in the world really wants that flat, uninspiring “t-sss!” of opening a screw-top, or the dull thud of a synthetic cork coming out of a bottle’s neck? 

And yes, there’s (pop!) science on this - in this case, regarding champagne:

“The research revealed that the most desirable ring of a cork pop is at a constant level between 8,000Hz and 12,000Hz, referred to as “brilliance” pitch by sound engineers.

Popping Champagne

Popping Champagne

This appeals to the human ear because constant frequency creates sounds comparable to cymbals and bird calls, whereas pitches with fluctuating frequency intensity cause rough noises, such as nails on a blackboard.”

It’s a tough situation for anyone trying to shift away from cork, and work is already underway to create a thermoplastic stopper that will make exactly this kind of pop as it’s pulled out. 

But - why stop using cork at all, if it’s what wine-drinkers really want to hear?

On the face of it, cork is the perfect solution to the problem of storing wine, and has been for centuries. It’s not clear who first invented it - we know 17th-Century vintners previously used oily cloth stoppers (which is curious, as cork had been used to create stoppers for casks at least 2,000 years ago). But for whatever reason, “cork” quickly became both the name of the stopper and the name of the material it’s made from - the bark of the cork oak tree. 

The land of cork oak is Portugal, our destination in May 2023 - the source of over half of all the world’s cork. And the place in the country where most of it’s harvested is west of Lisbon, where huge cork oak fields line the mountainsides.

Cork Oak Trees in Portugal

Cork Oak Trees in Portugal

Seeing cork being harvested is a strange mixture of satisfying & unsettling: the farmer chops into the tree, then turns their axe sideways to start peeling the bark off in huge sheets, essentially skinning it (an impression further reinforced by the exposed red “flesh” of the tree having an orange-red hue). It looks destructive - but cork is a sustainable resource. The tree survives (less than half its bark removed at any one time) and, 9 years later, will provide another crop of the same size. 

And there’s the environmental impact: once used, cork either rots down in your garden compost bin like any other form of wood, or can be recycled (but only by taking it to a dedicated cork recycler, like this one). Compared with the plastic and metal used in synthetic alternatives, cork is an eco-friendly triumph.

So why did those alternatives take hold? Well, as always with these things - cost was a big factor. With such a limited and localised supply, cork is relatively expensive stuff to use. It’s also, as a natural material, more fragile and prone to damage, particularly if it isn’t stored in perfect conditions before being processed into a finished product.

And then there’s the worst thing that can happen to your most prized bottle of wine (apart from someone else drinking it, obviously): you open it to find…that unmistakably wrong smell, somewhere between rank sweat and rotting cardboard. Somehow - and you may never know how, or what further damage has been wrought - it’s become tainted, better known as “corked”. 



What gets called cork taint might not actually be the fault of the bottle’s stopper - it could be a problem with storage, or impurities that have crept into the aging process somewhere. But alas, it’s probably from the cork. 

All cork contains a natural fungi, and when it comes into contact with certain varieties of chlorides, it triggers a chemical reaction that creates 2,4,6-Trichloroanisole or TCA. Unfortunately for traditional winemaking, those chlorides are often found in materials regularly used for cleaning - and since they’re so widespread, and since a single dose of TCA can go on to “infect” other bottles it comes in contact with, it’s not long before an entire stocklist is ruined, turning precious wine into cheap (or actually not-so-cheap) vinegar.

Avoiding cork taint is a priority for modern vintners, but it doesn’t have to mean ditching cork. Without the chemicals triggering the formation of TCA, cork is good to go - and there are excellent winemaking reasons to stick with it. Synthetic corks don’t expand or contract, so once they’re inserted under pressure, that’s more or less the end of the process. But natural cork lets a bit of oxygen in - and under stable temperature conditions, that’s the secret of capturing just enough oxygen to allow the wine inside to reach its full potential. 

(In fact, in a sense, this *is* winemaking. A lot is down to the cork working in perfect harmony with the contents of the bottle - a collaborative effort!)

Wine Bottle and Used Corks

Wine Bottle and Used Corks

And as we look towards the future and consider our warming world, check out cork’s ecological benefits as outlined by Lucy Siegle in The Guardian:

“The trees naturally occur in mixed-plant woodlands – the Rolls-Royce of forestry – and their root systems are excellent water regulators in this semi-arid landscape. They also anchor the soil and offer shade to the biodiverse species. According to a WWF report, the remaining 108,000 hectares of Portuguese cork oak forests are instrumental in preventing this region from turning into a dustbowl. 

Each tree sustains 100 species; it is pretty much the only place in which the rare short-toed eagle and extremely rare Iberian lynx will consider living. It is a living, breathing European ecosystem and effective carbon sink (conservative estimates say the cork forests sequester 10m tonnes of CO2 every year) and really, how many of these do we have knocking about?” 

For economic reasons, synthetic alternatives will be around for a while yet - and who knows, they may even be perfected until they’re true rivals to cork, including on environmental grounds…

But for now, there’s only one clear leader of the pack - and it makes exactly the right kind of *pop*.

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