Cork Tops!

For the last four years I’ve been at the heart of the current round of ‘cork wars’. During this time I’ve tried to take a scientific approach to which closure—cork, screwcap, synthetics or other new alternatives—offered the best options for wine. Although I haven’t endorsed one closure over another so far, when approached from a pure ‘Slow Food’ perspective that decision becomes much less complicated.

Let’s examine closures from a purely environmental perspective. Compared to all others, only cork is completely derived from a renewable resource and is totally biodegradable. Because modern cork plants are powered by their own waste, both the production and recycling of cork products require relatively low energy input.

In terms of global warming, cork forests are are regenerative and present a net carbon sink. Cork trees take a good decade to mature, are harvested once every eleven years, and have a production lifespan that is well over a century. Just as importantly, they like dry, infertile, relatively desolate habitats. In the near future, the cork forests of North Africa, Spain and Portugal may be the only thing holding back the Sahara Desert.

Equally important, cork forests also arrest cultural desertification. A symbiotic relationship exists between free-range ‘pata negra’ pigs, the cork forests they live in and the people who tend both. Acorn seeds dropped by cork oaks are crucial to the pata negras’ diet and essential in determining the distinctive flavours and textures we all enjoy in Iberian ham. If people weren’t busily employed tending cork trees and pigs—as they have for centuries—rural communities would dry up and depopulate off to big industrial cities.

Compared to this, alternative stoppers (plastic, synthetics, screwcaps) require energy hungry, environmentally destructive manufacturing processes: bauxite mining, aluminum processing’s huge electricity consumption, oil, etc. And, of course, each of these materials presents major long term disposal and recycling problems.

From a purely environmental perspective there isn’t a lot to debate here. Given a choice between a bauxite mine, an oil well or a cork forest, which would you want in your back garden?

All the warm and fuzzy stuff aside, from a wine drinkers perspective the most important closure issue concerns what delivers the best quality.

Terroir is about preserving the soul of a wine. This requires leaving as much of its point of origin and genetic makeup intact for as long as possible in the winemaking process, and then delivering it into bottle with an stopper that encourages further development in the most positive way possible. Following on from this, terroir focused winemaking should be custodial, low impact and non-interventionist in nature.

Countering this, screwcaps are fundamentally anti-terroir in nature. Screwcaps start from a manufacturing process intent on radically altering a wine so it can be safely stored under a metal capped container. Screwcaps are all about ‘the tail wagging the dog.’

This approach is required because screwcaps’ near ‘anaerobic’ nature imposes chemical changes on wine a year or so after bottling, that result in a fault called ‘post-bottling sulphide reduction.’ This dresses wine with a range of unpleasant (struck flint, burned rubber, rotten egg) aromas and creates bitterness on the palate that mutes fruit and shortens length of flavor. Eventually dominating a wine’s own self-expression, post-bottling sulphide reduction casts a sort of vinous chiaroscuro haze that obscures all underlying expressions of terroir. In the end it speaks more of itself than a specific soil type or place or vintage or variety.

From the start screwcap advocates misunderstood the underlying chemistry that causes this to happen., thereafter they failed to recognize the severity of the problem. Without getting into complicated chemistry, suffice it to say the traditional solution to sulphide reduction is to expose the wine to oxygen which reverses the ‘reductive’ process and cleans up negative characters. A considerably less desirable ‘stopgap’ option is to ‘fine’ with a ‘heavy metal’ in the form of copper sulphate (a potential toxin), which strips out sulphide compounds temporarily diminishing the problem.

Because screwcap advocates champion anaerobic post-bottling maturation, an oxygen solution proved philosophically unacceptable, so instead they have favored a chemical solution, suggesting wines should be ‘prepared’ by regularly copper fining just after fermentation, followed by repeated doses during maturation until the wine is perceived to be clean enough to bottle.

Historically, copper fining has always been considered a radical treatment that should only be used as a last resort to salvage an undrinkable wine; the proverbial ambulance at the bottom of the cliff scenario. There are good reasons for this. Copper sulphate indiscriminately targets bi-products of yeast fermentation, sulphide compounds (called thiols) which are responsible for producing both positive and negative aromas, flavors and palate characters in wine.

The problem here is that in targeting ‘bad’ sulphides with copper sulphate, winemakers are also stripping away all the ‘good’ sulphides that give a wine its distinctive terroir character. Native yeasts—one of the purest expressions of terroir—are especially rich in sulphides, most particularly the dangerous ones that can turn bad under screwcaps near anaerobic environment. But even sulphides produced from inoculated yeasts are unique expressions of the relationship between grapes, soil and climate. Copper fining strips away these fundamental connections to terroir, effectively disrupting, distorting or destroying a wine’s DNA fingerprint.

The craziness of all this is that today consumers clearly want less chemical additives, where screwcap supporters are enthusiastically offering more.

Craziness tips over into insanity once it’s realized the simple alternative to screwcaps’ ‘heavy metal’ approach is—oxygen. Throughout history, corks have provided a fairly benevolent environment for wines to mature under. Micro amounts of oxygen seep through cork providing a natural buffer against sulphide reduction which keep it from tipping over into smellier ‘reduced’ characters. The irony here is that it took the appearance of sulphide reduction under screwcaps to inspire scientific studies which eventually vindicated cork as actually quite wine friendly.

We know now from clinical trials that several forms of technical corks (Diams, agglomerates, twin disks, barrier covered cork, etc…) have found a sweet spot where a tiny ingress of oxygen consistently keeps post-bottling sulphide reduction at bay. And although synthetics also counter reduction well, they tend to oxidize wine far too quickly for long term cellaring.

Natural corks too do an excellent job of foiling sulphide reduction. Contrary to the wild claims made by screwcap advocates that natural corks suffer from bottle variation rates of 1000-1227 fold, recent scientific research has confirmed now that variation is no more than 3-4 fold—not that far off screwcaps. And within that 3-4 fold range, oxygen ingress is near to or slightly above the same sweet spot that technical corks manage.

On the other hand, both corks and technical corks have suffered from unacceptable levels of TCA taint in the past which also obscures terroir. Five to ten years ago this was a major issue, but steady reforms within the cork industry have greatly diminished this problek through preventative and curative measures. CO2 washed Diams appear to have eliminated TCA altogether and many of the H2O steam washed technical corks have reduced TCA to below threshold levels. New developments suggest powerful curatives will extend to full size natural cork in the very near future (Amorim applies its ROSA Evolution wash to natural cork in June 2007). Increasingly, cork derived TCA is looking like a historical phenomena.

For more than two centuries, winemaking, wine maturation and, indeed, wine styles have been closely allied to the mechanical and chemical properties of cork. Indeed, without cork humanity would never have defined the concept of terroir. Where a few years ago cork looked like it was staggering along on its last legs, it now seems to have picked it self up by the bootstraps, dust off its nastiest habits and seems to be facing a relatively bright future. And from a Slow Food perspective, that’s a good thing.

Paul White is an American freelance wine writer and editor currently based in Wellington New Zealand.

First published in the Italian magazine Slowfood, no. 25.