How does a condenser work in whisky making?

A condenser cools the hot alcohol vapour coming from the still, so the vapour becomes liquid again and runs on into the distillery as distillate.

The vapour leaves the still via the lyne arm, the pipe at the top of the neck. That pipe leads to the condenser, where cold water takes away the heat. Without a condenser the vapour would simply disperse. The Scotch Whisky Regulations 2009 prescribe that single malt Scotch whisky is distilled in pot stills and comes off the still at a strength below 94.8 percent. The law says nothing about the cooling itself, and it is precisely in that free space that a distillery steers the character of its distillate.

A shell-and-tube condenser is a copper shell with about a hundred thin copper tubes inside, through which cold water flows while the vapour around them cools and condenses.

The vapour enters at the top and keeps touching cold copper on its way down. Because so many tubes fit in a single shell, the copper surface is large. That is exactly the purpose of this design: a lot of copper in little space, in an upright cabinet next to the still house. According to ScotchWhisky.com, more copper is available in this system than in a worm tub, and that is where the difference in flavour comes from.

A worm tub lets the vapour run through one long copper coil that lies outside the still house in a tub of cold water, sometimes as much as a hundred metres of pipe long.

The water cools that coil from the outside. The vapour therefore condenses early in the pipe, after which the liquid trickles the rest of the way down without touching much copper. There is thus less copper available in this system than in a shell-and-tube condenser. About twenty Scottish distilleries still work this way. A worm has many joints and a leak is hard to find, so the water in the tub is checked for alcohol.

Copper binds sulphur compounds from the vapour, so the longer the vapour touches copper, the more heavy and meaty elements disappear and the lighter the distillate turns out.

A shell-and-tube condenser strips those compounds from the vapor more thoroughly than a worm tub does. The distillate comes out lighter and more floral. If more sulfur is left behind, as happens with a worm tub, the distillate keeps more body and a meatier character. Copper also acts as a catalyst in the formation of esters. A distillery therefore chooses its condenser not out of convenience, but to maintain a consistent house style.

The temperature of the cooling water helps determine how much copper the vapour touches: warmer water in the tub gives more copper contact and therefore a lighter distillate.

With a worm tub this is harder to control than with a modern condenser, because the outside temperature, the water temperature, the flow rate and the individual character of each worm all play a part. A distillery therefore keeps a close eye on those values. On our shelf in Bathmen, bottles from both systems stand side by side, from worm tub to tube bundle. Feel free to ask when you are looking for a bottle with more, or less, body.