What makes whiskey so delicious?
As Brunning points out, these flavorful compounds come from a number of different parts of the production process.
Lactones and aldehydes come from precursor molecules present in oak, which are then transferred into the liquor as it's aged in oak barrels.
Many Scotch whiskies also have a characteristic smoky flavor that comes from phenol compounds. These phenols result from the peat moss that's burnt to dry out barley before it's fermented.