It depends on who you ask, but a general consensus says that somewhere between 60 and 80 per cent of the character of the whisky we drink may be due to the influence of casks during maturation. ‘You can make good spirit,’ the old saying goes, ‘but if you don’t fill it into good wood, you won’t get good whisky.’ Gavin D Smith wraps up his series on whisky’s production with part two of his look at the magic of maturation
‘To listen to the silence of 5,000 casks of whisky in the twilight of a warehouse while the barley seed is being scattered on surrounding fields, might make even a Poet Laureate dumb.’
From Whisky and Scotland by Neil M Gunn
Not only is the wood itself of great importance, but the type of warehouses in which whisky casks are stored can also have a significant impact on the ultimate character of the spirit.
Traditionally, Scotch whisky was matured in ‘dunnage’ warehouses – relatively small and built of stone or brick, with slate roofs and earthen floors, containing casks stacked no more than three high on wooden rails or runners. Most distillers and blenders would agree that such structures offer the optimum conditions for maturation, providing consistency of temperature and humidity.
However, with space usually at a premium, the bulk of whisky is matured in much larger, concrete-floored warehouses which hold up to a dozen casks between floor and roof on racks, or in premises that store casks upright on wooden pallets. These are much more cost-effective and convenient for handling using fork-lift trucks than warehouses of the dunnage variety.
ABOVE: Casks maturing in a classic dunnage warehouse at Wolfburn on Scotland’s north coast
WHAT'S IN A WAREHOUSE?
In ‘racked’ or ‘palletised’ warehouses there are temperature differences between casks stored close to the ground and those located near to the roof. Maturation occurs most rapidly in the warmest part of a racked or palletised warehouse, which is invariably the highest, and there is also less circulation of air when casks are packed tightly on pallets.
At Dalmore distillery, on the shores of the Cromarty Firth, north of Inverness, master distiller Richard Paterson and his colleague, master whisky maker & blender Gregg Glass, use dunnage warehouses No. 4 and No. 6 to mature the oldest and rarest of their whiskies.
“I think in damp warehouses, whisky becomes more mature, softer, and the rough edges are broken down,” says Richard. “In dry warehouses, the whisky can remain a bit sharper and hotter, and retain a degree of immaturity for longer.”
Whatever the style of warehousing in which maturation takes place, many commentators argue that the location of the warehouses has an influence on the character of the whisky we ultimately drink.
They claim that a cask of whisky matured next to the sea on Islay, for example, will have a slightly different character to a similar cask matured in the centre of the mainland.
Due to the scale on which large companies principally concerned with blended Scotch whisky now operate, it is not feasible for more than a small percentage of their malt whiskies to be matured at the distilleries where they are produced.
Centralisation of maturation operations – often in Central Scotland – has increasingly become the order of the day, though many distillers, particularly those operating on a smaller scale, will age spirit destined for single malt bottling at its ‘home’ distillery.
COMPLEX CONVERSATIONS
The process of maturation involves the porous oak casks ‘breathing’, with many changes to the spirit occurring due to the ‘conversation’ between liquid, wood and external atmosphere. Pungent sulphur compounds diffuse out from the cask, while air diffuses in, promoting a series of chemical reactions, with a proportion of the higher alcohols being transformed into esters and other complex compounds which have a beneficial effect on the character of the maturing spirit.
The rate of maturation and the amount of spirit loss varies according to temperature and humidity levels. In the cool and relatively damp climate of Scotland, a reduction in both strength and volume occurs as time passes, with an average evaporation loss of around two per cent per annum – usually referred to as the ‘angels’ share’.
During maturation, the previous contents of casks play a major part in influencing the character of the whisky being aged in them.
To generalise, a first-fill ex-bourbon barrel will impart toffee, vanilla and caramel notes to the spirit, while the influence of a second-fill barrel will be altogether more subtle.
Meanwhile, a European oak sherry cask will give raisins, prunes, spice and sherry, and an American oak sherry cask, with less tight graining, will imbue the whisky with sweeter vanilla, coconut, fresh fruit and spice notes.
As noted last month, casks which formerly held other alcoholic drinks such as wine, are also used at times, most notably to bring a form of additional maturation to whiskies which have spent the bulk of their existence in more conventional casks.
Virgin American oak casks have become popular in this respect, delivering sweet vanilla, oak and very spicy characteristics to the whisky ageing within it, while port casks may imbue cocoa notes, and Japanese oak yields cedar wood notes over time.
ABOVE: Richard Paterson says colour is of paramount importance, as a barometer of how much influence has come from the wood
A TASTE OF MAGIC
Apart from affecting aroma and flavour, time spent maturing will also alter the spirit’s colour. The clear ‘new make’ spirit filled into the cask will become anything from pale lemon to the darkest, richest brown, depending on the time the whisky spends in the cask, the age of the cask in question, the number of its previous fills, and, of course, the previous contents.
“Colour is of paramount importance,” declares Richard Paterson. “It’s a barometer of how much influence has come from the wood. The first time we see the colour is from the casks in the warehouse.”
In general, lighter-bodied whiskies will mature more quickly than fuller-bodied, more robust ones, and the type of cask used tends to reflect the nature of the spirit.
A delicate whisky could be overwhelmed by an oloroso sherry cask, while The Dalmore and The Macallan, for example, are perfectly suited to lengthy sherry cask maturation. The oldest Scotch whisky bottled to date is an 81-year-old Macallan!
As the interaction between wood and spirit is integral to the maturation process, smaller casks tend to mature Scotch whisky quicker. By contrast, large casks such as butts, puncheons or port pipes tend to require a longer period of maturation process, often upwards of a dozen years.
Maturation is, scientifically speaking, a hugely complex business. It is much better understood than used to be the case, but even now, not every nuance and variable of it can be totally explained by chemical formulae and equations, and perhaps that’s a good thing. Surely, we all like a little bit of magic in our dram?
“Colour is of paramount importance. It’s a barometer of how much influence has come from the wood. The first time we see the colour is from the casks in the warehouse.”
Richard Paterson
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