Oak barrels used for aging spirits are commonly charred on the inside to break down wood sugars, effectively caramelizing some inner layers of the wood. This facilitates the transfer of oak flavors (ie vanilla) into the aged spirit. There are different degrees of char that will yield different flavor results on the final spirit. The most commonly used char levels are #1 through #4. A #1 Char on a barrel corresponds to 15 seconds of fire contact. A #4, commonly called an alligator char, corresponds to 55 seconds of fire contact. Another benefit of charring oak is the filtration effect that the newly charcoal lined barrel can have on the aging spirit as this char can absorb some undesirable compounds. (Spirits/Production)