No one knows precisely why the size and shape of copper stills, which vary from distillery to distillery, play such a vital part in defining the character of the whisky.
But no one doubts that they do.
Which is why, when replacing or repairing a pot still, distillers will nearly always insist on replicating the original.
"In the old days, this could mean reproducing every dent and bump," says Richard Forsyth, managing director of Foryths, who have built and maintained generations of copper stills.
"But now distillers adopt a more enlightened view."
Forsyths (previously A. Forsyth & Son) have been in Rothes on Speyside since 1890.
Richard's grandfather bought the company for which he originally worked as a coppersmith, and carried on serving the many local distilleries.
Today the company's customer base is worldwide, with equipment designed and manufactured at the factory at Rothes shipped to countries as far apart as Jamaica and Japan.
In recent years it has successfully diversified into other market sectors, but the craft of the coppersmith remains at the heart of the business.
Forsyths built the existing copper stills at the Aberlour Distillery, and those that came before them.
At least once a year the stills are meticulously examined and overhauled - a "fitness test", Richard calls it - to ensure that they are in tiptop condition.
A key part of this is testing the thickness of the copper.
This used to be done by tapping it with a hammer, the state of the metal reflected in the sound made; nowadays they have ultrasonic equipment.
"As a rule of thumb," says Richard, "when the copper has worn to less than half its original thickness, it's time for a replacement."
Different parts wear out faster than others.
On the wash still, for example, the heads and condensers need to be replaced every eight to ten years, while the copper pot can last as long as 25 years.
With the slightly smaller spirit still, it is the other way round.
The head, swan-like neck and condenser last for 20-25 years, but the pot itself probably no more than ten.
It takes four coppersmiths about eight to ten weeks to construct an average size still.
The individual pieces of copper, hammered and shaped to meet exactly the required specifications, are welded together on site - whether it is Aberlour or Kentucky.
This is faster than using rivets, as they used to do, but no less demanding.
Indeed, despite the introduction of more sophisticated equipment, it still requires traditional craftsmanship, with each copper still having to be individually fashioned.
The skills of the coppersmith, like the pot stills they make, are passed on from one generation to another.
And Richard Forsyth is happy to report that there is no sign of the trade dying out, with plenty of young applicants eager to embark on the challenging five-year apprenticeship.
Good news for the copper still - and for the wondrous spirit that inhabits it....