Michel and Valerie Laroche have been putting screw tops from Alcan on their Chablis Grand Cru for the past five years. Back then their wine making neighbours and others frowned on the practice. But at a tasting of Chablis wines on Tuesday, another winemaker came over and made approving comments. "It's the market," he said. The decision highlights the ongoing debate in the industry between the traditional cork closure and the metal screw cap. While many big wine companies now have many of their lower ranges in screw cap, putting one on a premium wine is practically unheard of in the trade. Laroche's Chablis Grand Cru goes for about €37 when it is first released. Putting a screw cap on the brand was a difficult decision to make Valerie Laroche said in an interview. But it was a matter of survival for Laroche. Half of their Grand Cru was being spoiled by cork taint, a problem that causes the wine to take on a musty, unpleasant taste. Inperfect corks may also cause the wine to oxidise if they let in too much air. The couple were unable to find a reliable supply of good quality cork and so made the switch. "We now have better quality control," Laroche said, noting that the decision has not affected sales. The couple originally tried one type of screw top produced by an Alcan plant in France. They found that there was a problem with a little join inside the cap. They worked with Alcan to use a different closure more suited to wine. After testing the new closure for a few months, they made the switch. "It is a little more in price, but it is a better closure," she said. As part of the decision, the company's brochures also explain why the wine is capped with a screw top. The explanation is needed to help make it easier for customers to understand the decision, she said. The couple also decided to only put screw tops on 80 per cent of their wine. The wine still uses corks for tradition conscious markets like France. US customers are more accepting of a premium wine in a screw top, Laroche said. Laroche produces wines from Chablis, a domain near Beziers in the south of France, Chile and South Africa. According to figures quoted by Skalli & Cie, a beverage consultancy, aluminum closures account for about 6 per cent of those used in the wine market. Natural and technical corks hold a 74 per cent share, with synthetic corks accounting for the remaining 14 per cent. Franco Cocchiara, a manager at the Guala Closures Group, said the UK is leading the change toward screwcaps. In an article written for Skalli & Cie he noted that changing consumer preferences is driving the switch. For example more women appreciate the ease of using screw caps, he said. In New Zealand about 90 per cent of wine uses screw caps. In Australia use is set to reach about 50 per cent. In the US about 8 per cent of the wine is bottled using screw caps. VinExpo is the bi-annual wine and spirits convention for the professional trade, held in Bordeaux. The five-day show ended yesterday.