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At its simplest the closure on a wine bottle must keep the wine in and oxygen out. Tradition, regulations, cost, the style of wine, and consumer acceptability all influence the closure selected by the producer.

Traditionally, natural cork was considered the closure of choice, especially for any wine of quality. In truth, natural cork has many advantages. It is natural, flexible and compressible with amazing anti-slip properties. It is also biodegradable, 100% recyclable and, cork forests promote biodiversity. Most important natural cork has proven to be eminently suitable for long-term wine aging.

So why consider alternate options?

The biggest problem that cork has had to overcome is its susceptibility to TCA taint (2,4,6-trichloroanisole), a compound that contaminates the cork, causing a musty taint in the wine (think soggy wet cardboard!).

At a certain point it was estimated that up to 10% of all wine was affected by cork taint. That said, we all have different levels of sensitivity to cork taint. Some people do not taste it even if the level of taint is very high, while others can smell it almost before the bottle is opened.

The high incidence of TCA affected wines accelerated the search for alternate closures, which include various types of synthetic and technical corks, screw caps as well as glass closures.

While screw caps have been around for a long time it was really the New Zealanders and the Australians that pioneered their adoption for premium and super-premium wines. In fact in 2000, the winemakers in Australia's Clare Valley were so frustrated by cork taint that they collectively decided to bottle their entire Riesling vintage under screw cap. Such is the prevalence of screw cap in New Zealand, that some wineries have become 'cork-free' zones.

An important advantages of screw cap is that it really preserves the aromatic freshness and youthfulness of a wine. Screw caps are easy to open, and close, requiring no special equipment.

However, consumer acceptance varies. Many wine drinkers still like to hear the familiar 'pop' of the cork and, are not convinced that wines under screw cap will age as well, or as long, as wines under cork.

The historic decision in 2002 by noted Californian producer Plumpjack to bottle its ultra-premium 1997 Napa Valley Cabernet Sauvignon ($135) under screw cap was a huge endorsement for the closure. Since then many wineries, not just in New World wine regions, but also in more traditional regions like France, Italy and Spain are moving to screw cap, for certain wines, particularly, wines destined for early drinking, where freshness and bright fruit flavors are paramount.

Technical and synthetic corks are also used by many wineries across the globe. Unfortunately, some types have not proven to provide a good long-term barrier to oxygen, which can cause premature degradation of the wine. Hence, many of these types of closure are best suited to wines that will be consumed within about six to nine months of release.

Finally, glass stoppers are another option used by a number of wineries. As well as solving the potential cork taint problem, they are really quite attractive, and easy to open and re-seal. Their biggest negative is cost, hence they are not as widespread as other alternate closures.

So, are the days for natural cork numbered as alternate closures gain popularity and acceptability? Absolutely not. One of the best outcomes from all of this has been the accelerated research and development by cork manufactures such as Amorim to eliminate TCA. Through a variety of sophisticated, patented processes, the quality of natural cork closures today has never been better. Compared to five years ago, there has been a huge reduction in the number of cork tainted wines.

One thing that we can agree on, is that there will never be universal accord on the best closure for a bottle of wine. And that's okay, why would we want everything to be the same? What is more important is the relentless investment in improving the quality of all closures, so that winemakers can select the one that best suits both the style and the economics of wine being produced, and, that we as consumers can remain confident that the selected closure actually does its job of protecting the wine from any unwanted taint causing the wine to deteriorate before we have had the chance to enjoy it.

Natural cork, synthetic, screw cap and glass all have their place. Its fun to embrace them all. What's your view?

So, until next week, enjoy some good wines.

Mary

Images: Manincor Winery in Alto Adige - Moscato Giallo wine under glass closure; Amorim Cork Manufacturer; Alcan Packaging Stelvin Screw Cap; Supremecorq Vino-Seal from Closure Systems International; Amorim Cork Manufacturer