still, continuous , also known as the column, patent, or Coffey still, is used to make by far the greatest proportion of the world’s distilled spirits, although rather fewer of its luxury spirits. Continuous stills are highly efficient, capable of producing almost pure ethanol at high, and indeed continuous, volume, without having to stop to be charged with wash or emptied of stillage.
There are many small variations on the design, but all follow the same basic design, centered on a tall copper (or stainless steel and copper) column equipped with a number of perforated metal plates that divide the interior into discrete compartments. These plates are designed to capture condensing vapor and allow it to pool around the multiple perforations: each hole has a raised rim around it that prevents a portion of the condensate from simply dripping back down and is topped with a bubble cap that forces the rising steam to detour back down into the pooled liquid, condensing a portion of it. The contact between the vapor and liquid in the plates helps to strip the vapor of water and fusel oils. This process is called countercurrent reflux. See reflux.
During this process, an equilibrium is created where the ascending vapor is continuously enriched with the most volatile components, such as alcohol, while the descending liquid flow brings with it the water and other less-volatile components. The water-enriched liquid in the plates eventually descends back into the boiler, while the most volatile components in the vapor either reach the top of the column and enter into the condenser or, in a taller column, find their separate condensing places at plates high up near the top, where they can be drawn off as liquids.
Obtaining high-purity alcohol from a fermented mash is a complex process that requires separating many components based on their boiling points, volatility, density, and solubilities. In a pot still, this separation is accomplished over time, with the carefully controlled application of heat releasing one compound after another from the mash, so that the most volatile ones will pass through the condenser first and the least volatile ones last. Managed carefully, this can yield a heart of some 60–80 percent ethanol, but the process will take hours. It can be sped up by using very wide, very shallow stills and high heat, as Scottish distillers learned to do in the late eighteenth century when they were taxed upon the volume of their stills (the more charges they could run off in a day, the less tax they paid per gallon). But this came with a loss of quality and purity.
A column still solves this problem by separating the various fractions of the wash not temporally but spatially, so they are all vaporized at the same time, recondensing higher and higher up the column depending on their various condensation temperatures. As these temperatures are known, plates may be placed to catch them, and the chambers thus formed may be individually tapped as desired. Usually, it is only the ethanol compartment that is tapped, with a steady, unvarying stream of up to 95 percent ethanol being drawn off as long as wash continues to be fed into the still. For some spirits, however (chiefly American whiskies) the column is tapped further down, allowing various heavier congeners and more water to be drawn off with the ethanol. See
The distilling column at the Michter’s whisky distillery, Shively, Kentucky.
Courtesy of Michter’s.
History
The continuous still is a product of the early nineteenth century, but it is a fairly obvious development of the idea of steam distillation, which was already described and illustrated by the German-Dutch alchemist and distiller Johann Rudolph Glauber in the 1640s in the third part of his treatise on “philosophical furnaces.” His still was simple: a copper vessel full of water was heated in a furnace; the steam that generated was funneled through a pipe into the bottom of a wooden barrel containing wash; the vapor that rose from the wash exited the top of the barrel through another pipe and went through a condenser.
His invention, if such it was, seems to have lain dormant for over a century. At the end of the 1700s, though, there was an upsurge in interest in steam distillation, with one S. Thomas Wood receiving a British patent for steam distillation in 1785, the American Alexander Anderson patenting an “improvement in a steam still” in 1794, and Count Rumford suggesting distilling with live steam injection in 1802. In Britain, the excise blocked any practical application of this. In America, however, John Giraud had patented a “Perpetual Steam Still” in 1811; “Patent Steam-Distilled Rye Whiskey” was being sold in Baltimore by 1812; an improvement on Glauber’s still was being marketed in Nashville by 1817; and by 1829 steam-distilled whisky was being sold as the “common” grade, with pot-still whisky bringing a premium in price. In the form of the log still and the three-chamber still, live-steam distillation became the American norm until the 1860s, and remained so for rye whisky until World War II. See
Meanwhile, in France Jean-Édouard Adam and then Jean-Baptiste Cellier-Blumenthal (1768–1840) pursued a still that could run continuously using live-steam injection. It was the latter who first came up with the idea of using a column divided into compartments by permeable horizontal plates, in 1813 (he added the bubble cap two years later). See Cellier-Blumenthal, Jean-Baptiste. It took a while for Cellier-Blumenthal’s still, brilliantly simple and robust, to catch on. In the meanwhile, with excise objections overcome, similar but inferior stills such as those of Jean-Jacques Saintmarc (1826) and Robert Stein (1828) were adopted in Britain, Saintmarc’s for gin (when the Nicholson company of London installed one in 1826, it became the largest gin rectifier in Britain, apparently making some 18,000 liters of gin a day) and rum and Stein’s for whisky. (For a diagram of Stein’s most unlikely still, see patent still.) Then, in 1828, Aeneas Coffey, an Irish exciseman, patented a column still that was almost as simple as Cellier-Blumenthal’s and just as effective. It had the advantage of splitting the column in two, making it much easier to install, with one column—the “analyzer”—dripping the already heated wash through valved plates into steam rising from the bottom, and the other—the “rectifier”—feeding the vapor into the bottom so that it could heat the wash running down through the still in a serpentine tube and collecting any condensate on its own set of plates.
Pros and Cons
By the 1860s, after dozens of patented variations and minor improvements, the technology of continuous distillation was essentially perfected (today’s column stills differ only in detail). Column stills were turning out London gin; demerara rum; Glasgow, Belfast, and Ontario grain whisky; French beet spirit, German potato spirit and korn; Russian vodka (beginning in the 1870s); American bourbon; some Dutch genevers and Italian grappas, and a number of other spirits. Their popularity with producers wasn’t just because of the impressive cleanliness and purity of the spirits produced; it was also the volume. In 1833, the ten largest distilleries in Scotland used pot stills. By 1846, seven of them had replaced their pots with columns. The ratio of capital expense to output was less than half that of a pot distillery.
And yet a number of spirits, also produced by canny businesspeople, did not switch: cognac and Scottish malt whisky resisted to this day; American rye whisky largely kept its three-chamber stills until World War II; Irish whisky and Jamaican rum only brought in columns in the 1950s. Looking farther afield, tequila, Peruvian pisco, Batavia arrack, and baijiu all stuck to their pot stills as well. It is no coincidence that among these spirits are some of the world’s most highly prized: spirits that are considered a cut above in quality and that bring a premium price per liter even fresh off the still. For spirits whose selling point is rich, deep flavor, the quick distillation a column gives seems to release less flavor than long boiling in a pot, even if the column is tapped lower down to catch more congeners. But in 1908, when a British parliamentary commission listened to weeks of testimony to establish whether it should limit the definition of whisky to the pot still product, it decided not to, and rightly so. There is a place for both kinds of spirit, each delicious in its own way.
Forbes, R. J. Short History of the Art of Distillation. Leiden: E. J. Brill, 1948.
Gillespie, R. “Steam Still” (advertisement). Nashville Clarion, September 9, 1817, 3.
Glauber, Johann Rudolph. Furnorum philosophicorum pars tertia. Amsterdam: 1651.
Leopold, Todd. Communication with David Wondrich, May 20, 2021.
“Patent Steam-Distilled Rye Whiskey” (advertisement). Baltimore American, January 29, 1812, 3.
Weir, R. B. The History of the Distillers Company, 1877–1939, Oxford: Clarendon, 1995.
Willkie, H., and J. Prochaska. Fundamentals of Distillery Practice. N.p.: Division of Education, Joseph E. Seagram & Sons, 1943.
By: David Wondrich and Darcy O’Neil
The distilling column at the Michter’s whisky distillery, Shively, Kentucky. Source: Courtesy of Michter’s.