Most whisky lovers have long been content with buying a bottle or two of their favorite label and building up a small collection. But as the demand for Scotch whisky soars globally, a growing number of whisky fanatics have started buying entire casks for up to $1.6-million.

Sales of Scotch whisky have been on a tear lately. Scotland’s distilleries are enjoying a boost from the surging popularity of the tipple as more people are drinking cocktails and hard liquors such as whisky, gin and tequila. But a newer trend has emerged: a sharp rise in the sales of casks bought by whisky collectors and investors, particularly in Asia. And many of those are turning to consultants to help find casks, with some collectors snapping up as many as 100 of them.

All Scotch is whisky made in Scotland and more than 90 per cent of it is sold abroad. Last year, those exports hit a record £4.37-billion ($7.29-billion), roughly equal to 1.23 billion bottles. Sales of rare Scotch whisky products, the favorite of collectors and investors, are up 46 per cent this year and on track to top £36-million, an eightfold increase in just five years. Interest has grown so much that earlier this year, a group in Sweden created the first publicly traded whisky fund to buy an inventory of bottles and casks for investors.

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“We’ve seen a strong growth in the cask sales over the last five years,” said Euan Mitchell, managing director of Isle of Arran Distillers Ltd. outside Glasgow. The company’s cask sales have gone from fewer than 100 annually to around 300 and this year it’s selling 700 casks from a new distillery that’s opening next year. Those casks cost £6,000 apiece and once the whisky is made, the barrels will be kept at the distillery for a minimum of 10 years to allow the booze to mature. After that, cask owners can either have their whisky bottled or kept in storage longer. They can also sell their cask at any time, opening up what Mr. Mitchell believes will be a lively secondary market. “People are actively looking at alternative places to invest their money and they see the cask offer as a fun investment, a lifestyle investment and something that’s going to be interesting to be part of as the whisky matures and changes over the years,” he said.

Cask sales from top Scotch distilleries such as Macallan, Highland Park, Ardbeg and Bowmore have also become a key segment of the rare whisky business which has typically centered on bottle sales, according to a recent report from Rare Whisky 101, a Scottish firm that tracks the whisky market and brokers sales. “We forecast this part of the market will continue to develop quickly for connoisseurs, collectors and investors,” the report said. “To that end, we are now very active in sourcing casks of Scotch whisky, predominantly malt, ranging in age from 10 to over 50 years and covering all the regions, styles and iconic distilleries.” The firm added that it had already brokered cask deals worth £1-million and that some of its clients have acquired more than 100 casks.

Open this photo in gallery Whisky enthusiast Andy Bell at the shop he manages, Inverarity One to One, in Glasgow, Scotland, Aug. 16, 2018. Jeremy Sutton-Hibbert/The Globe and Mail

Until now, buying casks wasn’t easy. Most distilleries have been loath to sell casks of mature Scotch whisky, preferring to bottle the liquor themselves and reap the larger profit from bottle sales. Some distilleries have arranged private cask sales to wealthy customers, but those deals have been rare. Several new distilleries have sold casks to help cover startup costs, since making whisky can take up to 20 years. But those deals also tended to be private and risky, since buyers couldn’t be certain the distillery would stay in business. Now, the market is about to open up to a wider clientele.

Next month, Mulberry Bank Auctions in Glasgow will hold the world’s first public auction of mature-Scotch whisky casks, some containing liquor that’s more than 30 years old. “It’s something that we thought would be a really interesting type of sale to have because a lot of people are very interested in whisky casks as both an investment and from a bottling point of view,” said Stewart Smith, a whisky specialist at Mulberry. “And the problem is that it’s actually difficult to get hold of casks unless you are in the trade or have very high net worth … This is our way of making this side of the market accessible to people.”

Mulberry plans to auction a dozen casks on Sept. 19, including a “Macallan 1989 Hogshead,” which could fetch up to £200,000. The auction house will help arrange bottling for buyers or continued storage in Scotland (casks have to remain in Scotland to be considered Scotch whisky). And they hope to hold similar sales twice a year. “The idea of buying aged whisky is that you’re not having to wait as long to get a return. So that’s one of the main reasons for this type of cask sale,” he added.

Getting a return on a cask can be difficult. Whisky ages at different rates and each year about 3 per cent is lost to evaporation, known as the angel’s share. The type of cask is also critical. Most distilleries use old bourbon casks because bourbon can only be aged in new casks, meaning that once the cask is used, it’s discarded. Some also use old sherry, port or rum casks, which all affect the flavour of the whisky. Buyers also have to keep a close eye on the alcohol content. If it falls below 40 per cent, it’s no longer Scotch whisky and is worthless. If everything does work out, the investment can be lucrative as some casks hold up to 300 bottles.

Andy Bell has been hanging on to a cask of Scotch whisky for 16 years. His parents bought it for him as a gift when he turned 21. “My parents wanted to give me something important,” recalled Mr. Bell, who lives in Glasgow. “They said ‘Do you want a cask of whisky or would you like driving lessons?’ I have no interest in driving at all. So I said ‘I will take the cask of whisky,’” Mr. Bell has become an avid whisky lover, amassing a 300-bottle collection and doing valuations for a whisky auction house. He’s now managing a spirits shop in Glasgow called Inverarity One to One that specializes in vintage whisky. “ We’re seeing an increase in the [demand for] casks because there’s only a limited amount of [fine whisky],” he said, adding that the returns can be impressive. His parents paid just £750 for his cask and it could easily be worth more than ten times that amount now.

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Mr. Bell isn’t sure what he’ll do with his cask. He’s considering auctioning it off or striking a deal with a bottler. But for now, he’s letting it age and he’s keeping close tabs on its maturity. He sips samples every few years and he even poured out a large glass for friends to share the day after his wedding in 2010. “Every year, it’s been getting better,” he said.