The unthinkable has happened. So much whisky is being exported that warehouses are being emptied and distilling companies are having to ration supplies.

The shortage affects only the industry's most expensive brands - 12-year-old and older malts - sales of which are booming, especially in the world's fastest-growing economy, China. Production in the 1990s, when they were first distilled, hit a low. Hence the shortage and a £500million boom in building new distilleries and expanding old ones.

Emrys Inker, spokesman for the Edrington Group, makers of the Macallan, the world's third largest-selling whisky by volume, said: “It does look as though for certain ages of single malts, demand is exceeding supply. We can certainly sell everything we have got at the high end of the market.”

He said that sales of Macallan and Highland Park, another Edrington brand, had been particularly strong in the four countries believed to have the strongest potential for economic growth - Brazil, Russia, India and China.

“For this year's brands, particularly Macallan, there has been some form of rationing or allocations to these markets,” he said.

Total whisky production in 1993, a low point in the industry's recent fortunes, when distilleries were being closed, amounted to 351million litres. Worldwide sales of all whiskies in 2007, including much younger blended varieties, totalled 495million litres.

The most spectacular growth in sales has been in the Far East. In 2007, Singapore, from where goods are distributed throughout east Asia, imported 47 million bottles of whisky, a 121 per cent increase on 2006. The rise in popularity of malt continued in 2008, with a 5 per cent increase in worldwide sales. The total value of whisky exports last year is expected easily to beat the 2007 record of £2.8billion.

The promise of this liquid gold has led to a rush of investment. The Scotch Whisky Association, a trade promotion body, believes that about £500million is being spent on expanding distilling this year and in the previous two years. Six new distilleries are being built, three old ones are being revived, and three well-established names are expanding.

The smallest new distillery is Kilchoman on Islay, an island which already has plenty of whisky makers. Set up by two local entrepreneurs, it aims to take distilling back to its origins by using barley grown on the farm where the stills are sited and malting the grain on the premises.

Kilchonan is one of a few distilleries planning to break the self-imposed rule that malt whiskies must be at least 10 years old. It plans to sell its first whisky - a three-year old malt - later this year. Macallan, which has expanded its distilling capacity by a third, is contemplating blending various ages, including some younger than 10 years, under a non-age specific label.

The Kilchonan distillery is a world away from the futuristic £40million distillery that has been built at Roseisle, Moray, by Diageo, a drinks multinational. It looks like a super-tanker that has been beached up against a petrochemical complex which, on closer inspection, turns out to be an older malting works and the reason for the distillery's location. The only familiar things about it are the copper stills and mash tubs buried deep inside its formidable exterior.

The 10 million litres of alcohol it will produce (Kilchonan plans just 60,000 litres), expanding Diageo's whisky production by about 12 per cent, will be used for blended whiskies, including the top-selling Johnny Walker range. It will not compete with the company's 18 single malts, which include more traditionally distilled names such as Talisker.

Charles Allan, Diageo's malt whisky and Scotch heritage director, said: “What Roseisle allows us to do is to incorporate everything we have learned about Scotch whisky and to design a fit-for-purpose distillery.

We have designed it to produce the highest quality whisky we can make.”

Mr Allan attributes the exports boom in whisky - and growth in single malts in particular - to the big growth in middle-class populations with money to spend on branded products in the world's emerging economies.

A purchase of a top-range whisky, he said, “sends out a signal to everyone around in a bar or a restaurant that I am doing well and able to enjoy the things consistent with my social standing”.

While Mr Allan acknowledges that there are some supply issues relating to 12-year and older malts, he maintains that Diageo's wide range of brands targeted at particular markets means it is coping with the rising demand.

But all the distillers seem confident that the current sales surge will not be reversed by recession. “The long-term horizon for Scotch whisky is extremely positive,” Mr Allan said.

Times Recommends

• Times Christmas appeal: Letter from the Editor
• Conferences — what a waste of money
• Schools supremo learns a painful lesson