Corks, Screw Caps, or Other Solutions?

Corks, screw caps, and other ways of sealing bottles are referred to as closures in the wine business. But there’s no closure to the debate over the best way to seal a bottle of wine. The most common methods are natural corks and screw caps, but others include cork agglomerate, cork-shaped plastic, crown caps (as on beer bottles), and glass. Alternative forms of packaging wine, such as bag-in-box and metal cans, have their own specific closures.

In antiquity, it was discovered that the bark of the cork tree was ideal to seal bottles. When the cork was cut slightly larger than the opening and squeezed to fit, the cork expanded to provide a tight seal that prevented air from getting in. Although cork dries out and loses its elasticity, bottles could be safely stored on their side to keep the wine end of the cork moist.

But the perfect seal turned out to be less than perfect. Cork is sometimes infected by a compound, 2,4,6-trichloroanisole (abbreviated TCA), which gives wine an off smell. When wines are severely “corked” in this way, the smell (reminiscent of mustiness or new leather) dominates the aromas and flavours of the wine. Even when the taint is mild, it dulls the bright aromas and flavours of wine.

Estimates of the incidence of corked wines vary, but in the 1990s, when the problem is thought to have been at its worst, it was widely accepted that about one bottle in 10 or 12 was affected. A test of 2,800 bottles by Wine Spectator in 2005 found that 7 per cent were tainted—about one bottle in 14. The cork industry has always argued that the real incidence was much lower.

Justified or not, allegations of high rates of infected corks, along with a shortage of good cork, gave impetus to the increase of screw caps.

The curiosity is that while some people are sensitive to cork taint, many people cannot detect it and happily consume tainted wine. Problem corks are thought to be less common today, and in 2018 one wine writer reported taint in 3.6 per cent of bottles sealed with a natural cork—one bottle in 28.

Justified or not, allegations of high rates of infected corks, along with a shortage of good cork, gave impetus to the increase of screw caps. They had been used sporadically since the 1930s, mainly for cheap, mass-produced wines. The main obstacle to the widespread use of screw caps was consumer resistance: many people thought that a screw-cap-sealed wine must be low quality, while others argued that the ritual of removing a cork was intrinsic to the enjoyment of a bottle of wine.

Over time, consumers in some countries—notably in Scandinavia, northern Europe, Australia, New Zealand, and Canada—accepted screw caps on everyday wines. Still, there is a belief that fine wines should be sealed with a cork. Resistance to screw caps on any wine remains strong in France, Italy, Spain, and many other European countries, as well as in the United States.

Meanwhile, the cork industry attempted to find ways of treating natural corks to eliminate TCA. The search goes on, and the latest solution involves heating corks twice and treating them with alcohol. Individual corks are sniffed by a human or a computer before they are shipped to wineries.

The question is whether it will make much difference now. It is thought that the failure rate of corks has fallen to between 1 and 3 per cent, but there is no evidence that wineries that adopted screw caps for their wines are planning to shift back to cork.

More pertinently though, many consumers have moved on and are used to buying wines for everyday drinking that are sealed with a screw cap. We have probably reached the point where many wine-drinking households in some parts of the world do not have a corkscrew at all.

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