The image of the large copper whisky still is iconic. Whether it’s in Scotland making Scotch whisky, or in America making moonshine and whiskey with an “e,” the copper still signifies quality and taste. But why, exactly, do distillers stick with copper on both sides of the Atlantic?
After all, stills can technically be made of anything — aluminum, iron, brass, stainless steel. Many of those metals are actually cheaper than copper and last longer. Yet those materials can’t deliver one thing (arguably the most important thing): consistently good taste.
“When distilling whiskey in copper, the copper reacts on a molecular level with the sulfurs put out by the fermenting yeast,” Broadslab Distillery writes on its website. “It ‘cancels-out’ the sulfur taste which would otherwise be bitter and not as smooth.”
Yeasts release sulphur when they’re doing their business. In a non-copper still, that sulphur stays with the liquid. With copper, the sulphur molecules bind with the copper, making hydrogen-sulfide, which becomes copper sulfate. The copper sulfate remains in the still rather than going out with the liquid, and is then cleaned out when the still is cleaned.
Removing the sulphur compounds allows the fruity-smelling esters (organic compounds that can give off recognizable aromas) to shine through in the finished spirit. The more interaction with copper, the more sulphur compounds are handled. That’s important for places like Glenkinchie in Scotland, pictured, where the spirit relies on fruity notes.
Over time, copper stills wear out. They’re expensive to replace, but it’s worth it. Copper stills are all about the taste.