The condenser is the part of the still used to condense the alcohol vapours (in other words, to turn them into liquid) by cooling them down. While for Vodka, Gin and Rum makers the condensing efficiency (and safety) is where most of the emphasis is placed, many Whisky and Brandy makers look at how different configurations impact the profile of the spirit itself.
The size, shape and temperature of the condenser can make a difference to the flavour of the spirit. In Scotch, there have been many trials around old fashioned “Worm tubs” comparing them to shell-and-tube condensers to judge the impact on New Make spirit character.
Much of the consideration lies around the length of the interaction between alcohol vapour and active copper, and how this influences whether a New Make spirit is light or heavy (the longer the interaction the lighter the spirit will be). It’s clear that the condenser configuration can play a role in prolonging or shortening the interaction.
Configuration aside, some distillers such as InchDairnie even play with different settings on the same apparatus and run cold water through their shell-and-tube condenser to make a heavy New Make, then switch to warmer water when they want to get a lighter character.