Many whisky makers and lovers agree that the type of cask and the circumstances and intensity of maturation account for a good 80 or even 90% of the whisky and its taste. This is not so far-fetched, because especially single malt whiskies are mostly matured in first- or second-fill casks, the other cask occupations are mainly used for blended malt and blended whiskies, whereby with increasing use of the cask its "performance" naturally decreases during its 50 to 60 years of life. This also means that so-called "first fill casks", i.e. casks whose original contents (e.g. bourbon whiskey, sherry, port, red wine, etc.) were filled accordingly and into which freshly distilled barley distillate ("new make" or "spirit drink") was then poured, usually at 63.5%, pass on more of their "previous life" to the whisky and often produce incredible results (e.g. the so popular "sherries").For example, the so popular "sherry bombs" with former sherry casks), but often dominate the distillery character, which many whisky lovers appreciate and look for more than the cask. In this respect, a cask that has been filled with raw whisky for the third or even fourth time can deliver a great whisky, in which the character of the distillery is more intense than the drink that was in the cask first. A matter of taste!
Rarer by global comparison, but quite popular with German distilleries in particular, are "Virgin Oak" casks, i.e. casks that did not contain any (other) alcoholic beverage before the whisky was stored. Mostly (in Scotland probably around 80%, in Ireland rather more) former Bourbon Whiskey barrels are used. This is followed by sherry casks, which are used less often nowadays than they were 30 or 40 years ago, certainly because worldwide consumption of sherry has since declined dramatically. As a result, the supply of sherry casks has declined and prices have risen, often putting the price of a sherry cask at ten times that of a former bourbon cask. Exceptions prove the rule, as there are of course differences in quality and other factors that influence the price. Good for the whisky producers in Scotland, Ireland and all over the world, who appreciate Bourbon Whiskey barrels as a maturing environment, that the Americans have a law according to which their corn whiskey may only be filled into fresh (i.e. first-filled) barrels made of American white oak. I.e. afterwards the barrels have to be disposed of; or sold to whisky producers.
Oh yes, maybe at this point something about the taste: Maturing in former bourbon barrels gives a malt whisky especially nice vanilla tones, great fruit tones (due to the "Obstler character" of the "New Make" sometimes more into the apple, sometimes more into the pear). Sherry casks often give spicier tones (like clove and/or cinnamon), dried fruit, purple fig (especially with very young intense "sherry whiskies"). Of course the type of sherry (mostly Oloroso sherry, but also the sweet Pedro Ximenez, the dry Fino or even Manzanilla and Amontillado are used) used can make a completely different whisky. And besides, sherry casks are also very much used "only" for a post-maturing ("finish"), which can usually last for about 6 months, but more rarely for a few years, as they usually not only give off a great taste, but also a nice, darker colour.
Finally, though, I'd also like to point out that of course WHERE the cask was stored also plays a big role: In a constant-temperature Dunnage Warehouse, but where (through open windows!) not only temperature and humidity fluctuations occur, but also where the proximity to the sea ensures that the salty components in the air also find their way into the cask and thus into the whisky.
In Scotland, by the way, mach speaks on average of an Angel's Share (what the Angels consume, i.e. what alcohol and liquid evaporates in the cask) of about 1-1.5% p.a., In the rock cellars of Michel Couvreur Whiskies in Burgundy it's surely over 5% p.a., in Taiwan at Kavalan rather over 15% p.a.! Although the casks there are stored "upright" to slow down the intensive maturation process a bit.
Cask or cask, Angel's share high or low, it's always worth trying something new. And when it comes to age, it gets "tricky" all over again. Objectively, you can't say that a 20 year old whisky is BETTER than a 12 year old of the same distillery, even though the former might be more expensive. Also a whisky without age statement ("NAS" = no age statement) can be a great whisky, maybe because good casks were used. So always taste with leisure and enjoyment and decide for yourself. SLAINTE!
Text from: Frank Jerger