KEY POINTS:
It was supposed to be the solution for the age-old problem of corked wine: the screwcap bottle.
But now red wine producers are tackling a bigger obstacle - the odour of rotten eggs.
Experts believe that one in 50 screwcap bottles or 200,000 bottles worldwide may be affected
by a chemical process known as sulphidisation. When the metal cap is opened, the consumer is hit with a smell of sulphur.
Tests on screwcap wines by the International Wine Challenge (IWC) in London found that 2.2 per cent of bottles were affected by sulphidisation - a chemical reaction caused by excess use of the preservative sulphur dioxide and a lack of oxygen.
The IWC found 4.4 per cent of cork-closed bottles also suffered sulphide problems.
The metal caps were brought in because faulty corks failed to seal bottles and let the contents go off or go flat.
Experts believe there is little problem with a screwcap bought to be drunk straight away, but that storing metal-capped reds such as a pinot noir or cabernet sauvignon may prove disappointing.
Dr Alan Limmer, a Hawkes Bay winemaker who has written extensively on the subject, told the Herald the sulphidisation could affect 20 to 30 per cent of screwcap wines whereas cork affected only about 3 per cent.
For that reason he did not use screwcaps in his Stonecroft wines.
About 90 per cent of wines produced in New Zealand are sealed with screwcaps.
Dr Limmer said he had warned winemakers about the potential problem and comments in the last year or two suggested that too many wines were being adversely affected, although some claimed the problem was nonexistent.
Wellington based wine writer Paul White said the screwcap problem was largely being ignored.
"I actually wrote about this three years ago."
Mr White said it was potentially a big problem for New Zealand wine producers who had embraced the screwcap technology much more so than winemakers in other countries.
He taught wine appreciation and on average 10 to 20 per cent of the wines tasted had been affected.
"It is as bad as corked wine ... you can taste a bitterness. It knocks out the fruit characters."
At worse the wine could "stink" and smell like eggs, he said.
Mr White said the problem was caused by tin lining in screwcaps.
Bill Spence, general manager of Matua Valley wines, disagreed the screwcaps were problematic.
Mr Spence said all the Matua Valley product was screwcap sealed and had rarely failed since being introduced almost 12 years ago.
"We find the wines have a freshness and are cleaner."
He said the debate was a "storm in a teacup" and did not believe the claims being made.
"I'd like to see the evidence."
The Times newspaper in London reported a leading wine analyst had confirmed the problem. Wine chemist Geoffrey Taylor, who tested 14,000 capped bottles a year, said he found low levels of sulphidisation in wines, likened by some drinkers to a smell of burning rubber, or spent matches.
The smell was easier for drinkers to spot than the chemical compound TCA, found in wine with cork taint, the fungal problem which triggered introduction of non-cork closers.
Warren Adamson, the UK director of Winegrowers New Zealand said: "This is the first time any official figures have come out ... New Zealand wines are only 1.7 per cent affected ... below the mean average of 2.2 per cent."
