Alcohol and some of the adsorption capacity
A method of cleaning carbon is to soak it in alcohol and re-distil it.
What percentage alcohol would you use?
It's a traditional way to recover both the alcohol and some of the adsorption capacity.
The principle is: alcohol displaces volatiles from the carbon, and then distillation separates usable ethanol from the concentrated heads/tails mix.
For the wash strength:
30–40% ABV is generally best.
At this strength, ethanol is still a good solvent for congeners but not so high that it simply clings to the carbon without leaching
impurities.
Too weak (<20%) and you’re mostly leaching water-soluble compounds; too strong (>60%) and recovery is inefficient.
Process would be:
Rinse the spent carbon with hot water to remove fines and water-solubles.
Soak it in 30–40% spirit, leaving it to equilibrate for 24–48 hours.
Drain and collect the spirit, then redistil slowly.
Heads will be quite concentrated, so make a sharp early cut.
You’ll recover a fraction of clean ethanol in the hearts, with the objectionable compounds concentrated in the first fractions.
This way you recover some neutral spirit and give the carbon a partial “refresh” — though performance won’t match new carbon.
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