How are whiskey and rum distilled? Two basic ways – pot stills and continuous (column) stills.
Pot stills operate on a batch distillation basis, in which one takes of the heads, hearts, and tails sequentially (as opposed to Coffey/column stills which operate on a continuous basis.)
Traditionally constructed from copper, pot stills are made in a range of shapes and sizes depending on the quantity and style of spirit desired. By law, cognac, Irish and Scotch malt whiskies, and single pot still whiskey must be distilled using a pot still. (Wikipedia)
What we see here next is a pot still with a packed column and a dephlegmator – a device for partial condensation of a multicomponent vapor stream. This animation was created by Decoy, and found on the Home Distiller forum.
When it comes to making rum, what’s the difference? “The pot still is the original way all spirits were made. The spirit reflects all of the flavour as adjusted by the cuts of the distiller. It is the only truly artisanal way to make a spirit. It can be sharp/weighty on the palate when young, and much better when aged.”
– from “The Lowdown on Rum With Richard Seale” Interview by Stuart P. from The Whiskey Exchange, 7/22/16.
For continuous distillation, you need to take off heads, hearts, and tails simultaneously.
The stripping section removes water. The rectifier separates molecules based on boiling points. Can be a single column with both parts stacked, or can be built as multiple columns.
A column still uses the process of fractional distillation.
Single column / continuous still / patent still / Coffey still
1 tall column that is plated or packed to create more surface area. This surface area will condense vapour that will then drop back into the still. It may have a small condenser in at the top to aid this reflux. Then the vapour passes into the condenser, and out comes the spirit (rum or whiskey.)
Seale writes “this makes a heavy spirit at low proof, much heavier than pot-still spirit. It is rich but lacks the elegance of pot spirit, and is why young French agricole rum is an acquired taste. It is like pot-still without the good cuts.”
This is a binary distillation tower, with trays with bubble caps, separating a feed stream into one distillate and one bottoms fractions. (Wikimedia)
The second column is called an analyser, it has plates, and is used for creating high alcohol rum going into the 90% range.
Seale writes “this makes a flavourful spirit at high proof. Much of the heavy oils are removed, making it more palatable younger. Blending with pot (as for whisky) is the classic strategy.”
Seale writes “makes light rums with little flavour. The antithesis of artisanal, and often doctored with wine/sugar to compensate.”
A word on the behemoth industrial sized multi column stills. These can produce a distillate up to 95% pure ethanol – since all flavours are stripped out at this strength, it is called neutral alcohol and can be used for either pharmaceutical purposes or general liquor production… Since the only way to get flavour into a neutral spirit is by using barrels or adding spices/adulterants, and all the intrinsic quality of the initial distillate source is lost, most true rum aficionados disdain such rums as being artificial. However, from the producers’ point of view, it’s massively economical and they can produce huge volumes of cheap rum
Here is a single column still, followed by a second distillation in a pot still.
Thanks to James Bednar for helpful discussions.
A Tale of Two Stills – A Response, by Richard Seale, 11/12/15