copper has been the main material used in the manufacture of stills since the fifteenth century. Initially it rose to prominence because it is a metal that is easily worked and conducts heat well. In recent years, however, it has been shown to have an active involvement in the creating of spirit character.
Not all stills are made of copper. The earliest distillers often used clay or glass, while stainless steel is used in the production of baijiu and shochu, for example. Some artisanal mezcal producers use wooden and ceramic bodies for their distillations, while Bundaberg rum in Australia has pot stills with cast-iron bases. Lead was widely used for repairing stills in the Caribbean in the seventeenth and eighteenth centuries, and even for condensing coils, before it was discovered that lead toxins leaching into the spirit was the cause of the fatal “dry bellyache.”
Copper is a reactive material and is believed to help remove potentially unwanted (sulfur-derived) compounds from the spirit. It can also help reduce mercaptan-derived off notes such as those that suggest rotting vegetables. Some phenolic compounds can also be reduced by interaction with copper. See congeners.
It is believed that the longer the spirit vapor spends in contact with copper, the less of these “heavy” compounds will be carried forward to be condensed. This process is therefore closely interrelated with reflux. This interaction between vapor and copper can be manipulated in a number of ways. The size and shape of the still, the angle of its lyne arm, its condensing system, the fill level of the liquid in the still, and the speed of the distillation will all have an impact. See reflux.
A distiller wishing to maximize copper interaction would ideally have a tall still with an upward-facing lyne arm, leading to a shell-and-tube condensing system. The still would then only contain a relatively small amount of liquid, which would be distilled slowly. See condenser.
The height of the still prolongs contact, and the upward facing lyne arm helps to increase reflux, while there is a large amount of copper in a shell-and-tube condensing system. The low fill means a greater head space, again opening up more opportunities for copper interaction, while the slow distillation increases the time for that interaction to take place.
Conversely, the ideal still setup for a distiller wishing to make a heavy spirit would comprise a small still with a downward-facing lyne arm, leading into a worm tub. The fill level would be high and distillation quick. All of these elements will reduce the amount of available copper.
Although stainless steel is used extensively in column stills, even there the rectifying column will contain copper. This helps to reduce the potential carcinogenic ethyl carbonate (EC). The copper could be in the form of the plates, which separate each reflux chamber, or the use of copper wool, also known as “sacrificial copper.” The shape of the bubble caps—which also can be made out of copper—in each of the chambers will also influence the vapor flow and create different forms of reflux and copper interaction.
Buxton, Ian, and Paul S. Hughes. The Science and Commerce of Whisky. London: Royal Society of Chemistry, 2014.
Handler, Jerome S., Arthur C. Aufderheide, Robert S. Corruccini, Elizabeth M. Brandon, and Lorentz E. Wittmers. “Lead Contact and Poisoning in Barbados Slaves: Historical, Chemical, and Biological Evidence.” Social Science History 10, no. 4 (1986): 399–425.
Russel, Inge, and Graham Stewart. Whisky: Technology, Production and Marketing, 2nd ed. Kidlington, UK: Elsevier, 2014.
By: Dave Broom