Jack Daniels is a 140-proof grain whiskey when it is poured into the aging barrel. Jack Daniels oak barrels are made of American white oak that is indigenous to Missouri. All Jack Daniels oak barrels are roasted at 450 degrees Fahrenheit for four hours, then flash-charred above a 1500-degree gas flame for four minutes. They are then steam-quenched to release the carbon (and extinguish the fire). The roasting process carmelizes the wood sugar before the flash-charring produces the charcoal. The steam treatment causes the charcoal to expand like popcorn, in addition to extinguishing the fire. This charcoal expansion creates trillions of very tiny bubbles, which TREMENDOUSLY expands the carbon’s surface area. Fresh Jack Daniels oak barrels have about 1/3 inch of char on their interior surfaces.
Jack Daniels whiskey is aged inside Jack Daniels oak barrels for four years. The barrels are kept packed inside wooden barns during this entire time. No artificial heating or cooling of the barrel houses occurs. The cooling and heating of the central Tennessee’s natural weather cycle causes the contraction and expansion of the whiskey along with temperature changes. When the whiskey expands, it gets forced into the barrel’s wood. When this occurs, the liquid dissolves tannins and carmelized sugars. When the whiskey contracts, it moves out of the barrel’s wood and back into the barrel’s interior. Carmelized sugars are what gives this whiskey its characteristic reddish-brown coloring. The whiskey penetrates about 3/4 of the barrel stave’s thickness. It is easy to see the penetration line on the stave of old Jack Daniels oak barrels. Jack Daniels uses each whiskey barrel only one time. Once the whiskey has been removed, the barrel is sold to other whiskey manufacturers, tobasco sauce makers, European winemakers, and the general public.
Once the aging process is complete, the whiskey is diluted to 80 proof before it is bottled. In answer to your question about charring and toasting… They are separate processes. Toasting involves baking the wood at a temperature of 450 degrees Fahrenheit in order to carmelize the wood sugars. Charring involves the actual burning of the wood surface in order to create charcoal. Hobbyists find it easier to use toasted chips to impart flavor, and pre-activated charcoal for clarifying purposes. These two procedures are combined into one stage process during formal barrel-based aging.