After the grain is cooked, when the fermentation is complete, but before the barreling stage, the whiskey-making process reaches its apex with distillation. This is what separates beer from spirit, concentrating aromas and flavors and elevating the alcohol to a level worthy of wood.

Whiskey stills are almost always made of copper, which is easy to mold and distributes heat evenly. More importantly, copper naturally reduces sulfur compounds in the liquid, creating a cleaner-tasting spirit. Even stills that are made with stainless steel on the outside usually have copper lining.

At its simplest, distillation requires little more than a vessel, a heat source, a pipeline to carry the vapors, and a second vessel to capture them as they turn back into liquid. But the equipment today’s distillers use is a good bit more complex. Understanding the different components of today's whiskey stills and how they work together can help explain why whiskies made from the same ingredients, with the same yeast and barrels, can end up tasting wildly different.

Batch Versus Continuous Distillation

Whiskey can be distilled through either a batch or a continuous process. Batch distillation takes place on pot stills, with the liquid going through the distillation process at least twice, and sometimes three times. The first still is called the wash still; the second, the spirit still.

Continuous distillation is exactly what it sounds like—no need to transfer the liquid from one still to another, as the entire process takes place in a tall column-shaped still, with perforated copper plates at intervals that allow liquid to descend as vapor rises. (Technically, some column stills are so tall they’re split into two or three separate shorter columns, but the process remains the same.) The Coffey still, named for its 19th-century inventor, Aeneas Coffey, is a type of continuous still that Nikka still uses to make malt and grain whiskies.

Whatever still is employed, the process of distillation promotes contact between the alcohol and copper to varying degrees, with the goal of creating reflux. This is when the vapor, which is full of flavor and other compounds called congeners, hits the sides of the still and condenses back into liquid to be redistilled. Less reflux means heavier compounds make their way out of the still; more reflux yields lighter compounds.

With the multi-plate continuous still, reflux happens more efficiently than in pot stills. But the advantage of pot distillation is greater variation of spirit character and flavor—more on that below.

Pot Still Parts: Neck, Boil Ball, Lyne Arm, Purifier

Pot still size and shape can make a tremendous impact on how the spirit turns out. Bigger pot stills promote more reflux and thus produce lighter spirit compared to smaller sizes, as do bulbous stills compared to slimmer ones. Because the distiller makes their cuts on second (or third) round, the spirit still’s shape matters more than the wash still, although pairs often will be more or less identical, with the wash still a bit larger.

The pot still’s neck—the part that rises from the kettle base, directing vapors upwards—can also impact reflux immensely. If the neck is straight-sided, vapor rises without much reflux, so that both light and heavy compounds alike make their way out. A lantern neck, like those on the stills of Glenkinchie, induces reflux; so do boil balls, like the ones on Glenmorangie’s stills. A handful of stills have purifiers, little receptacles on the still’s lyne arm that collect heavy vapors and pipe them back into the pot to be redistilled; spot them at Ardbeg and Talisker.

Column Still Contraptions: Down-Comer, Bubble Cap, Doubler, Thumper

Column stills are sometimes described as being like a series of pot stills stacked on top of each other. While colorful, the comparison isn’t perfect. But it does get at the basic mechanism of continuous distillation, in which liquid is constantly heated, turned to vapor, and refluxed to start the process again, over and over until the vapor is drawn off into the condenser.

Inside each tall column still are copper plates or trays, perforated with holes, with a pipe called a down-comer at one side or another. The down-comer allows liquid to flow down the column, while the perforations enable vapor to rise up through it. Some column stills include bubble caps, little toppers on the holes in the upper trays, which increase copper contact and thus reflux.

In most places, the column still’s work is done when the vapor exits to be condensed. But for American whiskey, there’s usually an extra step: sending the spirit through a doubler, a small, continuous pot still, which further concentrates alcohol and refines the spirit's aromas and flavors. If the spirit passes through at the vapor stage, this little pot still is called a thumper.

Condensers and Receivers in Whiskey Stills

As it comes off a still, new-make spirit is in its vapor state and must be turned back into liquid by a condenser. This can be a single copper coil placed in a cold-water vat—the delightfully named worm tub—or, more likely, a series of small pipes enclosed in larger pipes through which cold water continuously flows. Once in its liquid state, the spirit is collected in a receiver until there’s enough of it to barrel.

Making Cuts: Foreshots and Heads, Feints and Tails, Hearts

Receivers are also used to collect parts of the distillation run that aren’t suitable for maturing into whiskey. The initial part of the run, called foreshots or heads, contains methanol, ethanol’s deadly sibling. The last part of the run, called feints or tails, is lower in alcohol and contains the heaviest, most undesirable congeners, such as fusel oils. In the middle, the part of the run that will go into the barrel, is the hearts. Individual whiskeys’ profiles and characters differ thanks to varied cuts between heads, hearts, and tails. Some distilleries even collect the heads and/or tails to re-distill them with the next spirit run, extracting every last bit of useful flavor. Waste not, want not.

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