Copper is widely utilized in distilling due to its malleability, ease of cleaning, and capacity to transfer heat efficiently. Furthermore, copper acts as a catalyst in creating esters – which give Scotch whisky its distinctive floral and fruit notes – when alcohol interacts with carboxylic acids like fatty or acetic acids. Most sulphur compounds produced during fermentation are removed via contact between stills and condensers and copper surfaces as these come into contact.
Copper’s location within a still has a dramatic impact on reducing sulphur compounds, with wash still pot having the least influence and spirit still condenser having the greatest. Corrosion may play a part here; patinaed copper surfaces seem to have less of an effect but an uncorroded surface has greater effectiveness in this regard.
Another significant element in new make spirit production is the length of time rising vapours contact copper, as it will directly influence its quality. Longer and wider still necks allow rising vapours access to more copper surface area, thus decreasing the proportion of sulphur compounds found in final product.