Experts raise a stink over screw-top wine bottles

They have been hailed as a modern, cheap and safe way to seal wine.

But screw-top bottles could hide an unpleasant surprise for many drinkers.

In contrast to traditional corks, the caps stop the wines breathing, leaving them at risk of the chemical process of sulphidisation.

When the top is taken off, wine lovers are confronted with the reek of sulphur - likened to burning rubber or rotten eggs - rather than an attractive bouquet.

More than one in 50 screw-cap bottles sold in the UK could be affected by the problem, according to tests by wine experts.

Around 100 million of these containers of wine a year are sold in the UK, more than matching the number sealed with cork.

This means more than 2.2 million will suffer from sulphidisation.

The wine industry claims that using this modern method is safer, cheaper and more reliable than cork.

Many producers switched to screw caps about five years ago because of increasing concerns over cork.

It can be affected by a mould - trichloroanisol - leaving as many as 4.4 per cent of wine bottles with an unpleasant smell and taste. The problem with the screw caps was identified at the annual International Wine Challenge event at which tens of thousands of wines from all over the world are examined.

A test of 9,000 bottles found 2.2 per cent suffered from sulphidisation and other problems linked to the wine not being able to absorb oxygen, or "breathe".

When naturally occurring sulphides degrade in wine, they produce the compound thiol, which gives sulphur its smell.

Corks, however, allow in oxygen which neutralises the thiol.

The discovery throws into doubt chemist Geoffrey Taylor, whose laboratories analyse 14,000 bottles a year for the industry, said: "Screw- cap problems are around 2 per cent for Australia and double that elsewhere."

Experts said it would be possible to save the contents of an affected bottle by roughly tipping the wine back and forth between two jugs until the smell has gone.

Screw caps dominate New World wines while European producers have been slower to move away from cork.

Sulphides affect all types of wines, although they are a particular problem for reds.

Wine expert Martin Isark said consumers find it much easier to identify the sulphidisation caused by screw caps than problems with cork.

Consequently, they are more likely to return these bottles to stores.

"The everyday wine shopper would have no problem identifying a wine smelling like a stink bomb," he said.

Screw caps have tight-fitting seals which prevent the air from getting in.

Some wineries are working on designs with more room around the head of the bottle to allow air in.