At the Tales of the Cocktail convention this year, I moderated a panel with three distillers who run column stills; one 5-column rum still, one continuous bourbon still, and one pot-column hybrid.
Liza Cordero is the Process Director for DonQ rum, made at the Serralles distillery in Puerto Rico. She runs a pretty gigantic 5-column still. It makes DonQ rum and also custom products for other brands. The information below is from the seminar as well as what I've learned in my distillery visits around the world.
In my last post, we discussed how bourbon is made in a single column. The single bourbon column specializes in being continuous (as opposed to a batch-run pot still) and separating the alcohol from the water and from the solids in the low-alcohol beer that is put into it.
In a 5+ column still, this is also what is happening, but just in the first column or two. (It seems that columns can be split or divided in two according to purpose, or in some cases just to keep the height down so that airplanes don't hit them.) The center columns are for refinement of the spirit. The final column is for recycling of waste alcohols.
I can't claim to fully understand what is happening in each of the three middle columns exactly (yet!) but between the seminar, a detailed description of Grey Goose, and two Absolut vodka distillery visits it seems that the columns do five different things:
- The first columns separate solids from liquids, and the alcohol from water. The alcohol can be partially refined in this column above the level at which the beer enters the still (as mentioned in the previous post).
- In one (or more) columns they dilute the newly-distilled spirit with water and redistil it, and remove certain components. This is hydro-selection.
- In another one (or two) rectification columns they take out other components - "high and low oils". At Grey Goose, this is split into two columns; one that uses pressure to separate components and another than uses a vacuum.
- One column removes methanol from the final spirit.
- Sometimes a final column captures waste alcohols pulled from other columns and processes them into a recyclable form.
So that's what I think I know about multi-column distillation for high-proof products like rum and vodka. If you have any questions, let me know and I'll try to get them answered.