I believe it is present in both the original distillate and also is leached from barrels. Some info here on the leaching from barrels: AGING OF WHISKEY SPIRITS

I believe it is present in both the original distillate and also is leached from barrels. Some info here on the leaching from barrels: AGING OF WHISKEY SPIRITS IN BARRELS OF NON-TRADITIONAL VOLUME http://etd.lib.msu.edu/islandora/object/etd:1059/datastream/OBJ/view http://etd.lib.msu.edu/islandora/object/etd:1059/datastream/...