A core element in our tasting sets and events is exploring the roots of flavour. Although much of the flavour and colour of whisky arises during the long conversation between the spirit and the wood during maturation, it’s fascinating how the underlying character hugely depends on the nature of the still and condenser used to distil the spirit. The Science of Distillation blind tasting experience, which you can order as a gift set or sharing box, aims to demonstrate some of what this art can achieve.

Our Exploring Whisky blog series delves into the fascinating subjects around the production and history of Scotch whisky. We have already touched upon some fascinating histories, the impact of peat, the regions of Scotland and the first steps on the road to making whisky. Now we arrive at distillation, a method of separating and purifying substances that dates back thousands of years! Explore the ancient origins of distillation here, or read below for the fascinating science behind your favourite spirit.

Copper

Although each pot still in Scotland is unique, one thing they all share is copper. This is the perfect choice for a number of reasons, it is malleable, long lasting (a still can be used for 40-50 years) and a great conductor of heat. Its pitted surface catches and reacts with a variety of unwanted compounds in the vapour to help clean the distillate and rid unwanted sulphurs. Cyanides, carbonates, acids and sulphurs are all returned to the wash, and the greater the level of contact with the copper the lighter the spirit tends to be.

Before distillation, the wash is a complex broth of water, alcohol and a variety of compounds known as congeners. The art (and science!) of distillation lies in carefully controlling the process so that only desired congeners are retained in the distillate - though quite what these will be will depend on the characteristics being sought.

If you visit a distillery, it is common to see a spirit safe (pictured). This contains two bowls to catch the condensed vapour. The first flow of liquid during distillation (known as the ‘foreshots’ or ‘heads’) contains light, volatile compounds with low boiling points. Most of these are generally not wanted and get collected in the first bowl ready to be recycled into the next distillation.

After the heads have passed through, the distiller will direct the ‘heart of the run’ into the second bowl, ready for the cask. Finally the ‘feints’, or ‘tails’, start to come through. These contain most of the heavy, oily, least volatile and offer bitter compounds, so the distiller switches the flow back into the first bowl.

Capturing a small proportion of the congeners in the foreshots and feints will contribute to the character of the final whisky, so a key part of the distiller’s art is knowing when to cut in and out of the heart of the run. Traditionally, this would have been done by hand, but more modern distilleries are supported by automated systems. Yet experience and a good nose remain crucial.

The size and shape of the still and the manner in which the vapour is condensed also plays a crucial role. Glenkinchie’s large pot stills and traditional worm tubs lessens copper contact and results in the heavier, oily body you may find in their malts. The stills at Ardbeg, meanwhile, are very short and fat, making it easier for vapour containing heavier components to reach the top of the still, enter the lyne arm, and then pass through the condenser and into the spirit safe.

In contrast, the stills at Glenmorangie have the tallest necks in Scotland. This increases the amount of reflux (where some of the vapour condenses and falls back into the pot) so that only the lighter components make their way into the distillate. An upward facing lyne arm or a boil bulb will also increase the amount of reflux and promote a lighter spirit.

The huge diversity of stills and condensers is best appreciated by visiting a selection of distilleries, if you can. Most provide guided tours with offer fascinating insights into how particular design elements contribute to the character of their whiskies.

Yet all modern distilleries hark back in one way or another to the traditional copper pot stills and worm tub condensers used to produce illicit whiskies before the 1823 Excise Act. These were celebrated for their superior quality, possible because, being small and light so they could be easily moved and hidden from the taxman, the early illicit stills maximised copper contact. The use of small barrels for the same reason may have also played a part.

Order The Science of Distillation blind tasting set in our Whisky Club Series and explore the subtle differences created during distillation. Including six carefully selected single malts chosen to reflect the diversity created during distillation, a blind tasting guide, six information cards and the wax-sealed envelope for ‘the big reveal!’.