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02 February 2007
The wood makes the whisky - Part two
By
Dr Bill Lumsden
Indeed, many distillers believe that as much as 60-70% of the final flavour of a malt Scotch whisky is derived from the oak wood. It therefore goes without saying that using quality oak wood is vital. What do we actually mean by "quality" in this context? This can be split into four main sub-headings, as follows.
1) Previous use
As mentioned in Part 1 (unfiltered - Winter 2006), Scotch whisky distillers prefer to use a cask that has been used previously, usually for eithersherry, 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, resulting 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 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 qualityconscious (some may say even fanatical) of producers. Basically, slowgrowth 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 their quest for quality. Needless to say, 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".
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