October 15 2011 issue


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PAGES (69) October 15 2011

The Case of Cork versus Alternative Closures Benjamin T. Weinberg

Allen Meadows, founder of Burghound.com, believes alternative wine closures have attracted fans primarily because of past sins committed by cork manufacturers, who have been accused of selling products with unacceptably high levels of taint. Noted Australian winemaker Chris Ringland finds the screwcap to be a significant advance in wine-capping technology at all price levels. Clearly, the debate still rages over the efficacy of alternatives to natural cork.

Jesse Katz, head winemaker at Lancaster Estate in Sonoma, Calif., thinks the subject is sensitive because cork is the last material to touch the wine besides the bottle itself. “Once the bottle is corked, screwed, or otherwise topped, there is no going back,” he says. “Wine is a product that, in some cases, takes more than two years to create. That doesn’t even include time spent on the vine. If the closure affects the wine in any way, it’s devastating. Contamination can destroy all the effort that went into the product.”

Many wine lovers associate the use of alternative bottle seals with an effort by producers to protect against cork taint, caused most frequently by the chlorine-related chemical 2,4,6-trichloroanisole (TCA). Screwcaps and other alternatives seem to have won the upper hand in the public-relations battle, at least, having demonstrated much lower levels of TCA than natural cork in a number of studies. But researchers have yet to prove which system is actually best at protecting and preserving untainted wine. An ancillary benefit of this high-spirited conversation has been an increasing awareness of post-bottling wine chemistry. As Ringland says, “People really care, and most importantly, they care about the details.”


Cork is a plant tissue harvested for commercial use primarily from Quercus suber, or cork oak, a tree endemic to southwest Europe and northwest Africa. Composed mostly of suberin, a hydrophobic substance, cork is known for its impermeability, buoyancy, elasticity, and fire resistance. It’s used in a variety of products—most commonly, wine stoppers, which can be cut out of single pieces of bark or put together from finely ground particles (these are called technical corks).

Portugal accounts for about 50% of worldwide cork production. After a period of declining demand from wine producers due to the availability of cheaper synthetic stoppers, natural cork is now making a comeback. It is currently used to seal about 80% of the world’s annual wine production of some 20 billion bottles.

One reason for cork’s dominance is a cellular structure that easily compresses upon insertion into a bottle and then expands to fill the space. The interior diameters of glass bottlenecks tend to be uneven, making this ability to seal effectively through variable contraction and expansion an important attribute. Natural stoppers also allow small quantities of oxygen to interact with the wine over time, and thus seem best suited to sealing bold red wines purchased with the intent to age.

But cork’s weaknesses are also well documented, including the possibility of allowing uncontrolled oxidation as well as various types of taint. In addition, a separate tool is required for extraction—which can be both a blessing and a curse. And according to avowed screwcapper Ringland, “Perhaps a less obvious problem is the bark itself, which over time softens and crumbles.” Natural flaws, channels, and cracks in the bark can result in an inconsistent seal; in a 2005 study by Scorpex Wine Services, 45% of corks showed gas leakage during pressure testing.

Cork is generally regarded as environmentally friendly, with the benefits of sustainable production and easy recyclability. Carbon-footprint studies by Amorim (a leading Portuguese cork producer), Oeneo Bouchage of France, and the Cork Supply Group of Portugal have concluded that cork is the “greenest” wine closure of all. According to Amorim, a plastic stopper is responsible for 10 times more release of carbon dioxide than an equivalent cork, and an aluminum screwcap for 26 times more. Cork forests also help prevent desertification and act as habitats for various endangered species; in fact, environmentalists have lamented the loss of some forests to commercial crops such as eucalyptus.

Advocates of artificial closures point out that the inexpensive agglomerate corks are just granules and dust bonded with solvents, and that corks are no more biodegradable than synthetic products. Then there’s that annoying TCA problem. A recent study by the Portuguese cork-industry group APCOR showed a tainted-bottle rate of 0.7-1.2%. In a 2005 analysis of 2,800 bottles sampled at the Wine Spectator blind-tasting facilities in Napa, Calif., however, 7% of the bottles were found to be corked—an unacceptable ratio by anyone’s standard.

Major cork producers such as Amorim, Álvaro Coelho & Irmãos, Cork Supply Group, and Oeneo have recently made strides in developing methods to remove most of the offending TCA, including a switch from chlorine bleaches to peroxide for cleaning and the introduction of innovative treatments involving carbon dioxide or steam. Partly as a result, opposition to the use of alternative closures is still fierce in some segments of the winemaking industry. In March 2006, for example, the Spanish government outlawed the use of alternative closures in 11 regions for wines claiming Denominación de Origen status.

According to Katz, cork’s greatest advantage is really its sexiness. “Opening a bottle sealed with a cork has history on its side,” he says. “It takes a little longer to get the bottle open, it makes a pop when the stopper is removed, and then you have to go through the ritual of examining the cork to see what kind of information you can glean. The process is classic and will always have its place with wine. Of course, a certain percent of natural corks are tainted, which can quickly ruin the moment. That’s not so sexy.”

This potential for corked bottles is why, since the mid-1990s, a number of producers around the world have switched to alternative wine closures such as synthetic stoppers and screwcaps. Each substitute comes with its own set of advantages and disadvantages.


Synthetic corks are made from plastic compounds (recyclable in most communities) and are designed to look and pop like natural cork, but without the risk of TCA contamination. Disadvantages include a reputation for excessive oxygen transmission and the difficulty involved in extracting and reseating the plastic corks; some also impart a slight chemical flavor. Synthetic corks are generally produced by one of two techniques: injection molding or extrusion. A 2007 study by Victor Segalen at Bordeaux University showed that injection-molded synthetics allowed higher levels of oxygen permeation compared to natural cork and screwcaps. But a new generation of synthetics uses a system of nanocells to replicate the cellular structure of natural cork, in an effort to duplicate the oxygen-transmission characteristics of top-quality, one-piece natural corks.

Other alternative wine-closure systems manufactured on a commercial scale include:

  • Vino-Seal (known outside the United States as Vino-Lok): A glass stopper with an inert plastic O-ring developed by Alcoa, it creates a hermetic seal that prevents oxidation and TCA contamination. More than 300 wineries have adopted the Vino-Seal since it was introduced to the European market in 2003. Disadvantages are its relatively high cost (as much as 70 cents per unit) and the expense of manual bottling, due to the lack of compatible equipment outside Europe.
  • ZORK STL: Made by an Australian company, it consists of three parts: an outer cap with a tamper-evident clamp that locks onto the band of a standard wine bottle, an inner metal foil that provides an oxygen barrier similar to that of a screwcap, and an inner plunger that creates a cork-like “pop” on extraction and can be resealed after use. A variation, the ZORK SPK, is the first on-bottle, resealable closure for sparkling wines.
  • Crown cap: Traditionally used in the sparkling-wine industry as a closure for secondary fermentation, it is normally replaced with a cork after disgorgement. Some producers have recently begun using crown caps as their final closures. Although these are easier to open than the conventional wire baskets and corks, they eliminate part of the ceremony and mystique of sparkling wine and cannot be reattached without special equipment.


Screwcaps, also known as Stelvins after the brand sold by Amcor, come in several versions, with liners made of tin or Saranex. At Lancaster Estate, Sauvignon Blanc is the only wine bottled under screwcap rather than natural cork. “It’s a great strength to know that our juice won’t be tainted by the closure and that it will be kept fresh,” says Katz. “Screwcaps are better seals then cork. But there is this perception among consumers that only cheap wines use screwcaps. I think that is slowly changing, but there are still some prejudgments out there.”

The screwcap is now the predominant closure in New Zealand, thanks in part to a government initiative that promotes its use over cork. In Australia as well, the majority of non-sparkling wines are screwcapped. “These closures are cheap, simple to apply and use, and have great uniformity and durability of performance,” says Ringland. “Like glass bottles, they are easy to recycle and recover. I can see no weakness beyond the irrational negativity possessed by some customers.”

While screwcaps generally offer a TCA-free seal, they also reduce the oxygen-transfer rate to near zero. This can lead to reductive qualities that may suppress aromas or create unpleasant overtones—a problem that particularly affects grapes like Sauvignon Blanc, with its natural tendency toward reduction. Following studies by the Faults Clinic at the International Wine Challenge in September 2006, it was widely reported that one in 50 screwcapped bottles may be affected by the chemical process of sulphidisation, which can result in odors of burning rubber or rotten eggs. In Meadows’s view, vintners using screwcaps haven’t settled on appropriate sulfur levels low enough to avoid reduction in the bottling process. “This means that screwcaps and the like are better suited to wines that will be consumed in the short run—meaning out to two years,” he says. “Moreover, because reduction (for me at least) is much more annoying in reds than whites, it seems that alternative closures are more successfully applied to the production of white wines than built-to-age reds.”

Ringland, who has been bottling white, pink, and red wines under screwcap for more than 10 years, disagrees. “These wines have matured beautifully,” he says. “In the first few years, we experimented with different levels of sulfur dioxide at bottling, but I don’t really think that it makes any difference in the end. In fact, I’ve bottled several wines made without any sulfur dioxide whatsoever during vinification and maturation. Impermeability, which these closures ensure, has made these wines a different animal entirely. It’s a real, commercially viable approach.” Michel Laroche of Domaine Laroche in Chablis, France, who has also adopted screwcaps, notes that “extensive quality tests showed convincing results. Apart from protecting against cork taint, screwcaps are also clearly beneficial for wine aging, particularly in preserving aromatic freshness.”

Chester Osborn, chief winemaker and viticulturist at d’Arenberg winery in the McLaren Vale, Australia, is another believer. After sealing a selection of d’Arenberg red wines from the 2002, 2003, and 2004 vintages with screwcaps, he assessed their performance against cork in blind tastings conducted over several years. Osborn found the results to be conclusive: the screwcapped wines were fresher in style and retained more fruit character at all stages of maturity. “Each showed more fruit on the nose and had a sweeter midpalate,” he reports. “At no stage did they look hard or raw. The tannins still softened as normal aging took place, and we did not find any sign of oxidization or woody, cork-like aromas or flavors as were evident on some of the cork-sealed bottles.”


Ringland summarizes his argument as follows: “To propose that natural closures are superior because they somehow get back to the roots of wine is all very fine. So how far do we take the process of devolution? Do we demand an end to the use of modern transportation for the shipment of wine to customers in foreign markets? Refuse to employ temperature control in the vinification, maturation, shipment, and storage? We may find comfort in the romance, rusticity, and simplicity of wine, but every aspect of what we do in an advanced civilization involves development, experimentation, debate, and, hopefully, improvement. To decry this development is absurd and hypocritical.”

Meadows still suggests caution: “I’m not at all convinced that the situation is quite this black and white. While it’s true that the bulk of the technological innovations have come on the side of the alternative closures, cork manufacturers have not been completely idle. Hybrid approaches that utilize natural cork and composite materials appear quite promising, in particular the DIAM system—a form of technical cork, used primarily in the production of Champagne, that is made by grinding up cork, stripping all of the aromas out of it, and then molding it back together with polyurethane. It depends on whether you call DIAM an alternative closure or simply a cork derivative. But it is guaranteed to be taint-free, and the longer-term experiments (out to seven years now) appear to support claims that wines age just as well under DIAM as they do under natural cork.”

To frame the debate in terms more familiar to restaurant professionals: how do we deal with guests’ potentially negative perceptions of alternative closures? Sommelier Aaron Foster and wine director Todd Rocchio of Elway’s steakhouse in Denver think any fears of such reactions are overblown. “We like the dialogue that screwcaps and the like create at the table,” says Foster. “An expensive bottle under alternative closure always evokes comment.” Rocchio agrees wholeheartedly: “Sure, some of our expense-account businessmen joke about it, but even that conversation gives us an ‘in,’ which is hugely important in today’s ultracompetitive restaurant environment.”

As with everything else of significance in the world of wine, consumer preference will ultimately determine the proportion of bottles that will be sealed under closures other than traditional corks.