It’s hardly surprising that malts aged 40 years, and longer, are a rare and recent phenomenon, as 15 years aging was widely considered the limit for malts up until the 1970s.Consequently, more mature specimens of malt can be a case of serendipity as much as strategy. Overproduction in the 1960s-70s for example, proved to be a boon by providing additional stock that remained in the aging warehouses.Of course there were exceptions within the industry.“We’ve always had a policy to mature for 20, 30, 50 years, and have released 50 year old decanters since the mid-1980s,” says Gordon & MacPhail’s Ewen Mackintosh.Evolution of the malt market over the past 15 years has seen a broader range of older expressions, and growth of interest in them. Various distilleries continue to set a new personal best, with Auchentoshan’s 1962 becoming the oldest Lowland malt at 41 years of age, while The Macallan’s vintages span 1926-1973, with the 1926 bottled as a 60 year old.It’s always nice to include superlatives, and the most expensive malt is The Dalmore 62 year old, a bottle of which achieved a world record auction price of £25,877.50 in 2002. All 12 bottles of the original release have been sold.The oldest Scotch to be released is The Glenfiddich 1937, bottled in 2001 as a 64 year old (at the cask strength of 44% abv). Part of the appeal of such malts is the story they encompass.“The 1937 is like a time capsule. Back then we used more peat, as it was difficult to get coal at that time, so it’s smokier, with a dry, Highland smokiness,” says William Grant’s Jens Tholstrup. Retailing at £10,000 each, the original release of 61 bottles has been a triumph, as only three remain available.With the future supply of older malts being actively managed, the first item on the agenda is the character of the new make spirit.“Older Macallans are not dominated by wood in the way you’d expect. If it was a lighter style of new make spirit, it would be unlikely we’d be able to mature for so long,” says David Cox of The Macallan.Ewen Mackintosh continues this theme: “The character of new make spirit in the 1950s-60s was generally heavier, when distilleries used different barley varieties, floor maltings and worm tubs, resulting in a heavier new make spirit of suitable complexity. This has allowed these whiskies to be matured for longer without being overpowered by the cask. Today we carefully select whiskies for long term maturation, ensuring that they have enough body and complexity to develop in the cask.”With older malts developing up to 70 per cent of their character during aging, cask selection is a crucial factor.“The fill is probably more important than whether it’s sherry or bourbon. Most older casks I’ve come across have not had that much wood influence, being second or third fill, and so passed over at 10 or 12 years. And as they haven’t come on as well they’re left for longer,” says John Ramsay of The Edrington Group.Jim Cryle of The Glenlivet concurs: “Older malts are generally aged in second rather than first fill casks. You’re not getting as many extractives as quickly in a second fill as in a first fill, which allows the distillery character to show through, and you also see more evidence of oxidation in a second fill. In The Glenlivet, oxidation sees a richness and mellowness that wouldn’t be as evident in a first fill cask.”Oxidation is a consequence of casks breathing in ‘fresh’ air, and exhaling ‘saturated’ air. When air enters the headspace, ie. the area above the level of liquid in the cask, it dissolves into the spirit (oxygen being the key element). This sees esters, aldehydes and acids within the spirit continually reaching a new equilibrium. In terms of flavour profile, the spirit tends to become fruitier, more floral, balanced and mature.Meanwhile, evaporation of alcohol and water from the cask leads to a decline in alcoholic strength and volume. The evaporation rate varies depending on the type of warehouse, and a cask’s position within it.Awarmer, drier environment promotes a greater proportion of water loss, while colder, more humid conditions see more alcohol than water evaporating. For the first 12-15 years the evaporation rate is around two per cent per annum. This subsequently falls to around 1.5 per cent, with 30-40 year old malts even going below one per cent per annum.The final tally can be monumental. Acask laid down at The Balvenie on January 26th 1952, and emptied on September 6th 2002, lost 77 per cent of its original volume through evaporation. This equated to a loss of 173 bottles, leaving a total of 83 bottles released as The Balvenie Cask 191, aged 50 years.The exact influence of faster or slower evaporation rates is still not fully understood. However, diminishing alcoholic strength changes the proportion of water in the cask, and affects the equilibrium. A higher strength can result in more alcohol-soluble flavour compounds (such as vanilla) being derived from the oak.Meanwhile, a lower strength and relatively higher proportion of water in the spirit, may see more water-soluble extracts (including tannins) being extracted. However much knowledge and planning goes into the next generation of older malts, there aren’t any guarantees.“While we may increase the number of lay-down casks, what you can’t do is accurately predict how every cask will turn out, so a smaller number of casks will be suitable for longer aging than are laid down at the outset.“Ultimately the oak in which we are maturing our spirit is a natural, plant material, and whilst you can reduce the risks of an unforeseen outturn through careful wood management and tight specifications, you cannot eliminate them,” says David Cox.At least regular monitoring leads to a point when the master distiller can look forward with confidence.“After 15-17 years you know whether you’ve got the right casks for longer-aged malts, for the next 20 years or so,” says Allied Distiller’s Robert Hicks. With peated malts attracting such a devoted following, how longer aging affects phenolic compounds is another consideration.“They get masked and softened by the character of the cask, be that sweetness from a bourbon cask or the rich fruitiness of a sherry cask,” says Ewen Mackintosh. John Ramsay adds: “Phenol levels stay more or less as they were. It’s a case of more balance, rather than them breaking down.” Tasting different ages of a peated malt such as Laphroaig is a fascinating exercise.“The nose of the 40 year old Laphroaig is quite unexpected as the phenols are very quiet, but they come thundering through when you taste it. Ninety-nine per cent of Laphroaig is matured in American barrels, so you get more vanilla coming through, which softens the whisky and quietens the aroma. When you taste it you get a lovely vanilla mouthfeel, but the phenols come through too. It’s a wolf in sheep’s clothing,” says Robert Hicks.Older malts share a distinctive characteristic, a whopping retail price, justified on the basis of rarity, the expense of longer aging, and the master distiller’s expertise. The complexity of older malts can certainly be a sublime experience, and a rare instance when the term ‘unique’ genuinely applies.”Gordon & MacPhail’s 60 year old Mortlach is remarkably fresh. There’s a strong sherry and oak influence but the Mortlach character is still there. Aromas are floral notes, beeswax, sherry, and esters with bruised/fermented apples. The palate is dry with a smoky element, quite fruity, and sherry comes through in the finish,” says Ewen Mackintosh.How such malts taste also raises the question of how many are actually sampled. With some effectively a trophy purchase, cynics would say why worry about the taste, no one will drink it anyway. What kind of attitude is that?“We would not let anything leave the distillery that we’re not proud of, and that we wouldn’t want to drink ourselves,” says Jens Tholstrup. But then even a trophy purchase can translate into consumption.“It all depends on the culture of the market in which you’re selling it. The Far East is a very strong growth area for The Macallan, and quite a lot of this is for conspicuous consumption, by someone who can afford something special,” says David Cox.“In the United Kingdom more is bought as a gift or for collection; often people can’t quite bring themselves to drink it! Northern Europe has more of a collector mentality, with North America probably somewhere between consumption and collection.” Another option for bottling older malts also promotes consumption, rather than possession.“We’ve sold quite a few miniatures off our website shop, at an accessible price point; in those situations it will probably be drunk, often after being given as a gift,” adds David Cox.While everyone should of course drink malts according to personal preference, diluting older malts entails a significant risk of the whisky collapsing. Ewen Mackintosh tells a cautionary tale.“Adding water can make a rich sherry character fall down into rubbery, sulphurous notes.”And after all those years of aging, that would be truly tragic.