Copper: the noblest of distiller’s metals
It’s wonderfully photogenic for sure, but there are lots of substantive reasons why copper is the quality still-maker’s material of choice.
It conducts heat efficiently.
Even and controlled distribution of heat around a still makes for a good distillation. If the still material has a high level of heat conductivity then it will efficiently transfer the heat applied to the liquid. A low level of heat conductivity would mean the still takes longer to warm the liquid up, and slower to transmit a change in temperature. All in all, higher conductivity equals greater control. It’s like the difference between cooking on an electric hob and cooking on gas. Steel has a heat conductivity of up to 45 W/m K. Copper has 386 W/m K. Copper wins. Eight and a half times over.
One of the arts of the still-maker is the creation of still shapes that encourage reflux. Reflux is the process by which alcohol vapour rises and hits an area of low pressure, forcing it to the sides of the still where it comes into contact with the copper, re-condenses, and drops back into the still. More about reflux in a moment though. The malleability of copper means that the still maker can beat and shape it to create designs that maximise these low-pressure areas, maintaining structural strength to boot.
It improves flavour.
Sulphur is not typically the distiller’s friend unless you’re looking to imbue funky farmyard notes to your liquid. Yeasts in the mash fermentation process will typically produce the likes of Dimethyl Trisulphide, Hydrogen Sulphate and Sulphur Dioxide as by-products. Copper binds itself to these sulphurous compounds, ultimately forming Copper Sulphate which sticks to the inside of the still during the distillation. With a thorough cleaning afterwards that means the sulphurous notes are flushed down the drain rather than making their way into your bottle. Copper contact also contributes to the formation of flavoursome esters in the distillation process. The notes created during a distillation are a balance between all the flavours that you’re trying to achieve pre-distillation. Copper stills bring those together, fine-tuning them and eliminating notes that would be detrimental to the end result.
Flavour should be derived from the grain and yeast selection, the fermentation profile, as well as the distillation profile. The latter is where copper really shines – tuning the amount of copper contact that the spirit vapour comes into contact with by running a faster distillation (low reflux) or a slower distillation (high reflux), or by engaging a copper column (much more copper contact) makes a world of difference to the final result. Over time the copper walls are sacrificed to this flavour cause, which is why a well-used still will need to be replaced or repaired to stop it from sagging or buckling.
It doesn’t corrode.
Copper is classified in more generous element descriptions as a noble metal. That means that it does not react with water, and when it does slowly react with atmospheric oxygen the resulting copper oxide forms a protective layer which protects it from further corrosion. Given the climatic conditions native to Scotland, it is no coincidence that copper is typically preferred over more oxidative, corroding metals. Rust is definitely not a note we’re looking for in a spirit.
It looks beautiful.
OK, so we can’t entirely look beyond copper’s good looks. In shimmering light it dances. In warm light it radiates. The artistry of the still-maker in cajoling copper into beguiling shapes creates a theatre fit for distilling spirits to match. Orchestras. Minarets. Swan necks. Whatever you see, it’s hard to argue that another material would make for a more aesthetically pleasing distillery.
We’re sure you’ll agree.