It’s estimated by distillers that anywhere between 50% and 70% of a whisk(e)y’s flavour can come from the barrel that it is matured in. Logically one can conclude from that statistic that the cask used to mature the initial distillate will have a huge impact on the aromas flavours that one picks up when partaking of a sup.
The interesting thing about maturation in Ireland and Scotland is that the huge majority of casks (specialty productions like Midleton Dair Ghaelach being the rare exceptions) that are used to mature the precious liquid have already been used in the production of other alcohols. These are namely single-use bourbon casks and fortified wine butts from Spain and Portugal. In some cases rum casks or wine casks may also be used. It is estimated that up to 7L of the previous spirit will remain in a typical 500L barrel; what remains of this previous spirit will “diffuse” with the new spirit over time. Also, as barrels may be recycled and used again for whiskey, it is the “first-fill” that will impart the most flavour from the previous spirit.
For Irish whiskeys there are a broad range of casks in common usage, each imparting different flavours, and the skilled master blenders of each distillery have instinctive senses for how best a whiskey can be finished, or married in a different cask to enhance or add to its flavours. It’s an intricate practice, but for the sake of convenience we shall go through some of the typical flavours and aromas one might expect to find in Irish whiskeys finished in different barrels.
As bourbon whiskey, by law, can only be made in single-use charred barrels, it is thus not surprising that so many end up on the other side of the Atlantic. The charred effect serves as a filter for many of the more bitter elements of the spirit, while also being responsible for vanilla and woody notes that can be observed in whiskeys. As it is generally only younger Irish whiskeys that spend their entire lives in ex-bourbon barrels, some of the more characteristic flavours of butterscotch or fudge, that a whiskey might develop from longer stays in the cask, aren’t as strong.
Sherry finishing is relatively more common among Irish whiskeys than their Scotch brethren purely because of the fact of the larger amount of blended whiskies bottled at a minimum age and spending their cask-life in ex-bourbon American Oak. In Irish whiskey the most prevalent finisher is fortified wine though they are quite varied themselves so we’ll look at the most common:
This sherry is a common finisher in Ireland and can be found among most distilleries and their aged or premium offerings. As it is quite sweet, yet not overly so, the cask adds lighter fruit notes such as apples or apricots, as well as more sugared citrus hints (like marmalade), like those found in Bushmills 16 for example.
A very sweet sherry that is made after the grapes have been dried to be almost like raisins, thus concentrating the sugars. The result for a whiskey when finished in this kind of cask is an increase in the floral notes and most definitely its overall sweetness. There are not many Irish whiskeys on the market with a PX (Pedro Ximenez) finish, but the newer distilleries and their experiments promise some great new variations, such as Echlinville’s 10 Year Dunville PX.
A tricky finish to pull off but some examples, such as the Tyrconnell 10 Year Madeira Finish have mastered it and even Jim Murray was suitably impressed. Though Madeira can range from dry to sweet it seems the final flavours imparted by the cask are long-lasting notes of dried fruits such as figs and raisins.