Charcoal-mellowing refers to a process used to make Jack Daniel's Tennessee Whiskey. Charcoal Mellowing is what makes Jack Daniel's a smooth sippin' Tennessee Whiskey instead of a bourbon. The process involves slowly dripping the newly made whiskey through giant containers hard-packed with 10 feet of sugar maple charcoal. The process takes ten days, and during this time the Jack Daniels Tennessee Whiskey absorbs the essence of the charcoal, refining the spirit and giving it a unique flavor and aroma.