The curious case of the cork

There is no best way to seal wine, there are only better ways under different circumstances with different trade-offs.

There are all sorts of ways to keep wine in and air out of a wine bottle.  Wineries can choose between natural corks, composite cork stoppers, screw caps with tin liners, screw caps with plastic liners, plastic corks of many types and elegant glass stoppers.

Natural cork closures have a centuries-long heritage; however, they allow for a bottle of wine to be “corked” as the saying goes or suffer from TCA contamination (a substance used to sanitize the natural cork prior to bottling). A “corked” bottle has a musty smell and taste. The result is a flat, moldy flavour devoid of fruit-filled taste and aroma.

It is estimated that about 5-10% of wines available on merchants' shelves are “corked.” Some winemakers use certified corks that are treated to be bacteria free. This is a necessary expense as they can not afford the negative publicity and in today’s economic climate, winemakers can not afford to loose 5%.

Well over the last couple of centuries the wine industry has been using more and more cork, however as cork is harvested from trees that are approximately 6 to 9 years old the supply has not managed to keep up with the demand, this has led to a much higher use of pesticides and wood preservatives to get the cork ready sooner. These treatments on the trees are what most people are pointing at to account for the large increase in corked wine.

Synthetic corks, derived from plastic, appeared to be a viable alternative to traditional corks. However, their track record has been tarnished due to their inability to keep oxidation at bay for any real length of time, significantly decreasing the shelf life of a wine and short-changing the maturing process of select wines. Plastic corks usually won’t contaminate the wine, but they don’t always seal tightly over time, so the wine can be oxidized after a couple of years. The eco-friendly debate also comes into play here.

Screw caps provide the best seal for bottled wines, and eliminate the “corked” and oxidation problem in one fell swoop. While, screw caps do diminish the drama and romance of bottle opening it is well worth the sacrifice to ensure a taint-free wine that offers consistent aging, maintained flavour and freshness with optimum quality control. Screw caps are TCA-free, but they, can seal too tightly, with the result that the wine can suffer sulfur reduction, which gives it a rubbery or rotten egg smell, and screw cap wine can fail to develop as it ages.

Corks seem headed for the endangered species list for all but the most precious age-worthy wines.  Non-cork closures including screwcaps were nearly invisible just 10 years ago (with perhaps 1 percent of the bottled wine market), but this is changing quickly.

Screwcaps have long been associated with inexpensive wine, but this is no longer the case. Some of the top wines in South Africa have switched to screw caps. Paul Cluver, Tokara, Constantia Uitsig, Fleur du Cap and Iona are just a few of the premium wine producers that have been using screwcaps, and they have been raking in the rewards.

Economics is behind the move away from cork. Screwcaps are not remarkably cheaper than cork, but they avoid the loss of good wine to cork taint. A shipment of tainted cork almost ruined one of the American wineries some years ago and destroyed forever the reputation of its Chardonnay wines. It had to rebuild (successfully) as a Pinot Noir maker.  In Great Britain, it is apparently getting somewhat harder to find a natural cork in a popularly-priced wine because the supermarket buyers, who wield such market power, are strongly biased in favour of plastic and screw top closures. Like many in the business, they have been burned too many times by problems they associate with bad corks.

No matter what stopper winemakers use, they can never be sure that the wine they put in will be the wine that you pour out.

You might think that global wine market competition would have produced a “best practice” solution for wine closures, but the market is too complicated and diverse for that. The science may be universal, but the people (both producers and consumers the middlemen in between) have their own quirks. In France, for example, it is hard to sell a screw top wine, at least for now, because of the strong attachment to tradition.

Tradition, ageing of wine, quality and price aside the sound of a cork being pulled out of a bottle is still music to our ears.