While we cannot predict what will happen in each individual cask, we do know that approximately 70% of the flavor characteristics of Glenfiddich come from the wood and the time spent maturing in it. In Scotland, we predominately use two types of wood to mature whisky–American white oak (Quercus alba) and European oak (Quercus robur). American wood is the most popular, accounting for approximately 90% of casks used today, but it is important to remember that each different wood gives its own unique characteristics to the whisky. For example, Q. alba produces vanilla flavors (fruity, sweet) while Q. robur yields a rich, tannic kick. At the Glenfiddich distillery we take the base spirit, which comes off the still at 65.6% ABV, and add it into the casks. The wood casks perform three important functions to the aging of the whisky: 'subtractive,' 'additive,' and 'interactive.' The relationship between the liquid and the wood is one of the many intriguing aspects of whisky. After all, that mysterious and storied past is part of the allure of Scotch whisky!