It has long been a saying among distillery workers that the wood makes the whisky. However, only
in recent years has the truth of the adage been understood by sensory chemists.
Traditionally, the Scotch whisky industry acquires its wood, in the form of oak casks, from The USA, in particular Kentucky and Tennessee, and from the Spanish region of Jerez and its surrounds. Both American and Spanish oak are used for coopering the casks: American oak is usually better quality than Spanish, but does not possess the tannins that form the dark colours in some whiskies.
These casks have been once-seasoned either with Bourbon or Tennessee whisky, in the case of the USA, or Sherry, in the case of Spain. This seasoning prepares the oak to an ideal level of activity for receiving and maturing new make spirit that will become Scotch whisky.