Wine gets better as it ages. This is also true for many spirits especially whiskey. Popsci featured the story of the 50-year old Glenlivet single malt scotch and how five decades changes everything from its color to its taste.
The whiskey was first distilled in 1964 and the resulting spirit had a perfectly clear color that is practically indistinguishable with water. It had a cereal-rich flavor and was slightly smoky from the smoked barley from where it was made. It was also solvent-like and clearly needed to be aged a few years.
After fifty years the result is a whiskey with a deep amber color. The smoky aroma is now gone and the previously bright fruit notes have now matured into baked fruit notes. It has several characteristics to the whiskey like toffee, honey, caramel, and chocolate. In its 50-year journey, most of the alcohol in the barrel had evaporated already. This leaves the rest of the world with a highly prized stash of 100 bottles. Each one costs a hefty $25,000.
All spirits are influenced by the environment they are in. For the 50-year old Glenlivet, the compounds of the charred wooden barrels and the actual environment of the barrels have all played a part in producing this excellent single malt.
Barrels are toasted in Europe and charred in the US before aging whiskey in them. Charring creates charcoal in the barrel and it acts as a filter for undesirable flavors. Scotch whiskeys are typically aged in barrels previously used for bourbon or sherry. Bourbon, by law, must be aged in new American oak barrels but scotch sometimes uses European oak.
There are still unknown elements to aging spirits in wood but, according to Dr. Bill Lumsden, distiller of Glenmorangie and Ardberg Scotch, in a barrel "development of fragrance and complexity spontaneously happen, but the key reactions are believed to be catalyzed by the wood itself." The wood contributes flavors via three compounds: degraded lignin for vanilla flavors, lactones for butter, coconut flavors, and lastly, tannins for the "wood spice" flavors.
