MILLIONS of wine bottles which use screw-tops instead of traditional corks could be spoiled by a smell of rotten eggs or burnt rubber, experts have discovered.
More than one in 50 screw-cap bottles sold in Britain could be tainted because of broken seals or sulphidisation - a chemical reaction caused by excess use of the preservative sulphur dioxide and a lack of oxygen.
The findings mean drinkers still risk buying wine which tastes off even though modern screw-caps were meant to solve the problem of "corked" bottles.
Around 100 million screw-cap bottles of wine a year are sold in the UK and the figure is rising as it becomes a popular alternative to cork.
The annual International Wine Challenge (IWC) event tests tens of thousands of wines from all over the world including around 9,000 with screw-caps and many more with corks. It found 2.2 per cent of screw-cap closed bottles suffered sulphide or similar problems. The effects leave a nasty whiff of sulphur, likened to burning rubber, rotten eggs or burnt matches.
The results could mean problems for shops and restaurants because the smell is much easier for drinkers to spot than TCA - the chemical compound 2,4,6-trichloroanisole which is found in corked wine.
Although plastic "corks" are available, they are unsuitable for all but the youngest of wines, because they perish after a relatively short time.
Almost nine in ten wines from New Zealand now arrive the UK in screw-cap bottles - around 12 million bottles a year - but producers insist the "fault" rate is lower than for other countries, at only 1.7 per cent.
Warren Adamson, UK director of the New Zealand Wine and Grape Industry, said: "This is the first time any official figures have come out with regard to the sulphide problems in screw-caps. These are helpful for our producers and winemakers."
But wine taster and food and drink writer Martin Isark said: "Even with only 1.7 per cent faulty wines, that's over 200,000 faulty wines on our shelves. The everyday wine shopper has little idea of what TCA or cork taint smells or tastes like. And even if they do suspect the wine is below par, they have little confidence to take the wine back.
"Trust me - the everyday wine shopper would have no problem identifying a wine that smells like a stink bomb and would have every confidence in taking it back to the shop."
Sulphides exist naturally in wine. When they degrade they produce a compound called a thiol which is what gives sulphur its smell. Although the IWC found 4.4 per cent of cork-closed bottles suffered sulphide problems, corks allow oxygen into the bottle, which desulphides the thiols and stops them smelling, but screw-caps do not allow this. Excess use of sulphur dioxide during bottling can exacerbate the problem.
Easy to deal with sulphur smell
DETECTING a screw-cap wine with too much sulphur is much easier than spotting a "corked" wine, explained The Scotsman's wine expert and Master of Wine, Rose Murray Brown. But the problem is easier to deal with.
"If you aerate the wine a little by swilling it around the glass, the smell should disappear."
She added: "Most retailers have a policy which states that you can return wine that doesn't smell right, so consumers shouldn't feel embarrassed about taking it back."