Even the heather imparts botanical flavors that may come across in the whisky. The shape of the pot stills in which the whisky is made is essential to the final taste, although nobody seems to understand why. The size of the still, the angle of the swan neck at the top, the source of the fuel, all are thought to have subtle influences. So certain are distillers of this that when a still must be replaced, the old one is reproduced exactly, down to the dents it may have received during its use. Another defining factor is how the whisky is aged, not just the length of time but the kind of barrel it is aged in.
American distilleries are a main source of the barrels used to age wine and spirits worldwide.
Another major source is sherry casks from Spain. Some distilleries use one kind of barrel or the other exclusively, but most use a combination of the two. Washington is a good city for single-malt fans. Many local stores stock a couple of dozen single malts, but two, the Wine Specialist at 2115 M Street, Northwest, and Central Liquor Store at 726 9th Street, Northwest, regularly stock around 150 varieties. Enjoying single malts is not an inexpensive pleasure.