(Stuff) - More than 70 vineyards for sale as wine profits plummet. Export wine prices have slumped to a new low as the industry struggles to cope with changes wrought by a massive increase in supply of Marlborough sauvignon blanc. Latest Overseas Merchandise Trade figures show that wine exports have more than doubled in the past four years. That includes 47 million litres exported in the three months to September, a 114% increase on the same period in 2007. Although that has pushed the total value of New Zealand's wine exports up past the $1 billion mark, it has been accompanied by a sharp slide in the average price per litre, a major determinant of industry profitability.