The wood makes the whisky
As you enjoy sipping a rich, mellow, complex tasting single cask single malt (or even grain) whisky, you are bound to marvel at some of the flavours, and possibly wonder from where they originated. Well, the likelihood is that many of the flavours and textures you're enjoying have come either directly, or indirectly, from the oak cask.
One of the biggest experts in the theme, the Scotch Malt Whisky Society has bottled whiskies from more than 120 distilleries. The whisky made available exclusively to members are straight from the cask(s) they have spent their lives maturing in, undiluted and unfiltered.
“Many distillers believe that as much as 60-70% of the final flavour of a malt Scotch whisky is derived from the oak wood. Using quality oak wood is vital. That’s why on our bottles we always indicate in what type of cask the whisky was matured, for how long and what was the previous occupant, if any. The tasting notes that the Society’s Whisky Panel provides for each bottle, indicates precisely what we may expect from the content,” says Stephen Swinney, director of the Scotch Malt Whisky Society in Poland.
What do we actually mean by ‘quality’ in this context? This can be split into four main sub-headings:
1) Previous use
Scotch whisky distillers prefer to use a cask that has been used previously, usually for either sherry, or bourbon. Ex-sherry casks are less popular nowadays, partly due to supply issues, but mainly because the flavour from the sherry residue soaked into the wood tends to dominate the overall character of the whisky. Ex-bourbon barrels on the other hand, are regarded as allowing more of the individual ‘house’ character of a distillery to shine through.
2) Number of times the barrel is filled
The more times a barrel is used for Scotch whisky,the lower the level of wood extractives and cask-driven oxidation that result in the whisky. Wood extractives will typically give golden colours and sweet flavours such as vanilla, honey, coconut, caramel, biscuit and a range of desirable spicy flavours. Cask-driven oxidation is a series of complex, biochemical changes that take place in maturing whisky, the end result of which, typically, is a fragrant, floral ‘top note’, to the whisky.
If a barrel is used many times, clearly the production of many of these flavours will be lower, and the end result can sometimes be a whisky with a preponderance of dry, harsh and even bitter flavours. This is why distillers such as Glenmorangie and Laphroaig have very rigid wood policies, ensuring no over-use of their barrels.
3) Origin of the oak
The vast majority of oak used in the Scotch whisky industry today is either American oak (Quercus alba) or European oak (Quercus robur and Quercus petraea). European oak, sourced mainly from France and Spain, will typically have higher levels of compounds called hemicelluloses and tannins. Hemicelluloses are broken down during toasting and charring, yielding a range of compounds which give "toasty" and "caramelly" flavours. The tannins, on the other hand, are responsible for giving rise to more dry and astringent flavours, which are often manifested in Scotch whisky as interesting "leather" or "walnut" type flavours.
The lower level of tannin in American oak, combined with the typical charring process involved in the manufacture of bourbon barrels, give rise to flavours of vanilla, coconut and a sweeter, almost creamier,
texture on the palate when these barrels are used for the maturation of Scotch whisky.
4) Oak growth rate
Using the rate of growth of the oak tree (which can be assessed by examining the pattern of the annual growth rings visible when the tree's trunk is cut) to influence the flavour of a liquid contained within, is the domain of only the most quality-conscious (some may say even fanatical) of producers. Basically, slow-growth wood has a different internal structure, leading to a greater, more complex range of products on offer. This wood, when cut, will typically be seasoned in the open air for up to two years prior to use, again helping the release of full, rich flavours.
Many of the world's top wine makers will source this specialised and expensive type of wood, but to date, only Glenmorangie goes to these lengths in its quest for quality. The topic of wood and its influence on the quality of Scotch whisky is broad enough to fill several text books. This article has hopefully provided you with a "taste" for this subject, and has left you in no doubt that, in many respects, "The Wood Makes the Whisky".
The typical description of the Scotch Malt Whisky Society bottle includes though: colour, cask and information on which time it has been filled (e.g. first fill barrel, second fill hogshead ex Bourbon, refill sherry butt), as well as age, distilled date, strength, and outturn (number of bottles from the given cask, worth saying that Society’s whiskies are limited in quantity and therefore never to be repeated).