It's established in the Scotch world that the age of a whisky pushes it's price up. A MacAllan or Glenmorangie 18 will fetch a much higher price than their respective 12 year old versions.
Having tried a small number of 18 year olds, I've found them highly variable in quality, just as you would with those in the 12 category, but those which were of higher quality seemed to be more mellow and subtle than their twelve year old counter-parts. But that's only my understanding from a very small sample size.
So the questions are:
- What does aging a Scotch do to the whisky chemically?
- What properties do 18 year old Scotches tend to share for tasters?
- Are 18 year old Scotches ever crafted with special care, to make them superior aside from the aging process?