What is reflux and how does it influence Scotch whisky character?

Reflux is a physical process that occurs inside the still during the distillation process. As a liquid boils various compounds are vaporised and turn into a gas. These gases start to rise up the still, and if they reach the condenser they turn back into a liquid and are collected as distillate.

However, a compound will cool down (or lose energy) as it rises in the still. If it condenses back into a liquid while in the still, it will drop back down into the pot to be boiled again. This is reflux and the process amounts to a progressive refining, purifying action which develops sophistication of the resultant distillate, eliminating impurities and other baser, oilier elements.

The amount of reflux activity within a still massively affects the spirit character. More reflux leads to a lighter and more refined new make spirit, while less reflux leads to a heavier, oilier and denser new make spirit.

The following factors can all increase or decrease reflux and therefore affect the spirit character:

• Still size 
• Still shape
• Charge volume 
• Slope of the lyne arm

You can learn more about reflux and the factors which influence it in the Batch Distillation module of the Certificate in Scotch Whisky.