Bourbon whiskey gains its flavor from the interaction between a distillate of a distinct mash bill and the degree to which it is aged in a new, charred white oak barrel. Reactions between the distillate and charred oak occur slowly and whiskeys are typically aged between two and 23 years. A major cell wall carbohydrate in oak wood is cellulose, a B-1,4 linked chain of glucose residues that creates a foundation for cell ultrastructure. It is unclear whether cellulose degrades in situ during aging and to what degree. To explore this, bourbon barrels of different ages were sectioned and randomly sampled to obtain averages from the numerous staves that contribute to a barrel. Using a suite of histochemical and analytical techniques, we examined whether cellulose was being degraded or left inert in the charred interior of the barrel during aging. Histochemical analysis using confocal microscopy suggested that cellulose remained intact upon charring in a new oak barrel. However, after distillate entered the barrel, age-related degradation of cellulose was clear. By measuring acid-insoluble glucose (cellulosic fraction), we confirmed that cellulose was being hydrolyzed. We quantify the progression of cellulose degradation by age. Loss of cellulose in the charred fraction into the spirt could explain some of bourbon whiskey flavor and mouthfeel, with an estimated 3 to 5 lb sugar units extracted from cellulose across the barrel surface area over six years.

Funding Support: NSF EPSCoR