|Mid 1700's Caribbean Double Thump Keg Pot Still|
While generally associated with the backwoods whiskey still, the thump keg, or “doubler”, is a very old design element that probably arrived with the early settlers and was incorporated into the stills they built on arriving in North America. Indeed, some older European stills made use of what appears to be chambers that functioned as thump kegs, so the principle was surely well known to colonists from the British Isles and the continent. The thump keg is one of the most clever and iconic design elements of the traditional hillbilly still whose purpose, briefly stated, is to distill the output of the pot still a second time, without having to run the distillate through the still twice.
|Flow Diagram of Double Thump Keg Pot Still|
|A Glass Double Thump Keg shows How Gases Heat and Boil Contents|
of the Keg, Distilling the Contents
Some, including traditional moonshiners and the connoisseurs of single-malt, pot-distilled Scotch whiskeys, would probably argue that this separation is a bit too good, and that the column strips out too many of these tasty cogeners, producing a bland, albeit strong, spirit. They would maintain that properly-managed pot still set up with a thump keg can deliver just the right amount of these compounds to create a full-flavored, robust spirit that indeed has tastes rather than being a neutral spirit like vodka. To what extent this is true and how much is folklore is debatable, but it is inarguably the case that the flavor-changes between cuts that are less sharply pronounced and more of these flavors will be present in the final product.
In the Discovery Channel series, “Moonshiners”, former shiner Tim Smith maintains that his old family recipe, made in a modern distillery and distilled using a column still just doesn’t taste the same, and even invests several thousand dollars to install a high-tech thump keg to replace the fractionating column.