When filtering alcohol produced by stills we recommend diluting it down to between 40%-50% ABV.
If you are looking to filter above this recommend ABV it can be done, but it doesn't gain you any quality. Because the organic compounds (like esters, ketones and higher alcohols) we are trying to remove are more easily removed from water than they are from ethanol. So the polar functional groups on the esters, ketones and higher alcohols, are potentially stronger affinity to dissolve in water than the non-polar group's affinity to dissolve in ethanol. Therefore these compounds move into the water component of the diluted spirit and as a result are removed more efficiently by the activated carbon.
If you would like to store your alcohol at higher than 50% ABV, or prefer not to dilute it prior to filtering for another reason, you can. the storage of spirit at higher ABVs is not detrimental to the spirit.
Please note that we can't guarantee the quality of the final product if you wish you filter at a higher ABV, we recommend 40%-50% as we find this to the best percentage to filter at to produce high-quality alcohol.
If you'd like to read more about the filtering process please see our Pocket Guide - Filtering Spirit.