Cork or plastic? Hard to tell until it's open

Easy. One is stoppered with cork, the other with the same sort of screw cap found on soft-drink bottles.

Wine snobs searching for a corkscrew had better think again - the vintners at the exclusive Napa Valley winery have eschewed cork in favour of a metal screwtop lined with foam.

The cap will, in theory, keep an airtight seal indefinitely.

And it will prevent the wine from being corked - that malodorous fate that befalls between 5% and 8% of bottles sealed with a traditional cork.

Say it proud

A corked wine is not - as many people think - an inexpertly opened bottle with floating debris, but wine stoppered with a cork tainted with the chemical TCA, or trichloroanisole.

New World winemakers: Less bound by tradition

Yet despite not being prone to such problems, screwtops and plastic corks suffer from a serious image problem.

PlumpJack wants to turn around that downmarket perception, and has even set the price of its screwtop bottles above those of the same vintage with traditional corks.

"Of course we have a mind-set to confront," co-owner Gordon Getty has said.

"That's why I decided on one of our finest wines. We're making a loud statement."

Marketing nightmare

For many wine drinkers, choosing a bottle sealed with a synthetic stopper is on a par with cracking open a cask of vin du cardboard.

"This better not end up in a crown-capped bottle"

But chances are, a hunk of plastic will lie under the foil cap on that bottle of wine at the Christmas bash.

About one in 20 bottles sold worldwide have plastic corks, a figure which rises to one in three among the cheaper varieties sold in the UK.

The UK wine warehouse chain Majestic has stocked a screwtop wine from the Australian winemaker Penfolds.

But despite retailing for a respectable �5.50 - a good �2 above the average price Britons pay for a bottle of wine - customers were not impressed.

Bad taste

Supermarkets - purveyors of 75% of wine sold in the UK, much of it sealed under plastic - say cork poses quality control problems.

Favoured tipple

Wine sales overtook beer in 1999 Sales totalled �2.6bn in the year to October '00 AC Nielsen figures

Yet wine experts argue that plastic does not guarantee a taint-free wine, and the bottles are not always airtight.

Jane MacQuitty, of The Times, has said she can detect a hint of plastic in the wines.

She recommends drinking wines with plastic corks within a year of purchase - hence the dilemma for the makers of wines designed to be cellared.

Endangered habitat

Conservationists warn that the increasing use of plastic stoppers puts wildlife at risk.

Habitat at risk: The migratory song thrush

For centuries, woodlands in Spain and Portugal have produced much of the cork used by winemakers.

These trees provide shelter for more than 40 species of wild birds and other wildlife, says Hannah Bartram, of the Royal Society for the Protection of Birds.

Cork farming is sustainable because the trees are debarked every nine years, rather than chopped down, she says.

"Yet if these forests are no longer economically viable, they are less likely to be replanted as the trees die out."

At the society's request, Waitrose and Marks and Spencer have agreed to label wines according to the type of stopper used so that the environmentally concerned can choose traditional corks.

Diversify or bust

Producers are addressing quality issues by cleaning cork with ozone steaming, as opposed to the chemical baths of old, and oven-drying the bark after processing.

Bitter prospect: Could crown caps be the future?

But it is not known for sure how TCA gets into corks - it may be the residue of pesticides used in decades past, it may be due to processing or storing cork.

The Guardian's wine critic Malcolm Gluck, who favours screwtops, has said cork farmers must end their reliance on the wine industry.

In his Superplonk column last year, Mr Gluck wrote: "Sticking a cork made from tree bark in a wine made in 1999 is like producing a modern motor car with a starting handle."

But old habits die hard - it still seems that the more wine-buyers pay, the more they want to wield a corkscrew.