After dissecting so many spirits I got the idea that I could create a barrel proof rendering of a whiskey by using vacuum distillation paired with a second distillation. The non-volatile part would be separated from the volatile part then the volatile part concentrated in a typical copper reflux still and the two segments rejoined. The change would be a reduction of water and therefore an increase in proof and a concentration of aroma (there are some finer points where fidelity is lost).
In the process, I discovered that my simple glass laboratory vacuum still sucks and is not good at collecting the solvent (I think I know how to tweak it). Time is money and Overholt is cheap so I ended up merging two bottles into one. One bottle was vacuum reduced (using a simple aspirator-to-vacuum flask rig) as far as my patience would take it (from 750 mL to 180 mL, but next time I’ll go all the way). The second was was simply re-distilled at high reflux to 80% alc. The volatile part is not sensitive to heat, so using a conventional normal-temp-atmospheric-still does little to impact the aroma (this is true enough, but not really).
The sensory properties of each half are really interesting. A lot of what a barrel contributes to a spirit is not volatile so re-distilling an aged whiskey reveals something very close to the white dog that went into the barrel. The non-volatile parts were concentrated at about 60C and it was amazing to see how much aroma was there. The non-volatile aromas really seem to define Overholt. The vacuum reduced segment became really turbid and I was afraid I spoiled the color permanently, but after marrying the color went right back to the same beautiful barrel hue.
Unfortunately, patience got the best of me and because I only reduced the non-volatile half to 180 mL, I only ended up with a 55% alcohol finished product, but it still made a lovely Manhattan.
I was really impressed with the success of this technique and am going to pursue it further. Next up is Fernet 151!