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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #355861
Title: Liberation of recalcitrant cell wall sugars from oak barrels into bourbon whiskey during aging

Author
item GOLLIHUE, JARRAD - University Of Kentucky
item RICHMOND, MITCHELL - University Of Kentucky
item WHEATLEY, HARLAN - Sazurac Buffalo Trace Distillery
item POOK, VICTORIA - University Of Kentucky
item NAIR, MEERA - University Of Kentucky
item Kagan, Isabelle
item DEBOLT, SETH - University Of Kentucky

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2018
Publication Date: 10/26/2018
Citation: Gollihue, J., Richmond, M., Wheatley, H., Pook, V.G., Nair, M., Kagan, I., DeBolt, S. 2018. Liberation of recalcitrant cell wall sugars from oak barrels into bourbon whiskey during aging. Scientific Reports. 8:15899. doi:10.1038/s41598-018-34204-1.
DOI: https://doi.org/10.1038/s41598-018-34204-1

Interpretive Summary: lants contain large amounts of carbohydrates (commonly known as sugars and fiber). The fiber consists mostly of a carbohydrate called cellulose, which is a rigid network of molecules of a small sugar called glucose. Another component of fiber is hemicellulose, which is less rigid than cellulose and consists of about 7 different sugars. In the fiber of wood, cellulose and hemicellulose are abundant and hence are large potential sources of sugars. When bourbon whiskey is aged in oak barrels, components of the wood contribute to the chemical components of bourbon whiskey. The purpose of this study was to understand changes in the sugars and fiber of oak barrel wood, after barrel preparation and bourbon whiskey maturation. Different zones on barrel wood were analyzed for overall fiber content by microscopy, and wood sugars were quantified to measure how the amounts changed with aging and in different parts of a barrel. In the interior part of the barrel, which is charred prior to use, fiber changed in structure and decreased over time. Sugars disappeared from the interior part of the barrels aged for ten years. The results of the study indicated that the barrel charring and aging processes affect the wood fiber composition and release of sugars from wood into bourbon whiskey.

Technical Abstract: Oak barrels have been used by humans for thousands of years to store and transport valuable materials. Early settlers of the United States in Kentucky began charring the interior of new white oak barrels prior to aging distillate to create the distinctively flavored spirit we know as bourbon whiskey. Despite the unique flavor and cultural significance of “America’s Spirit”, little is known about the wood-distillate interaction that shapes bourbon whiskey. Here, we employed an inverse method to measure the loss of specific wood polysaccharides in the oak cask during aging for up to ten years. We found that the structural cell wall wood biopolymer, cellulose, was partially decrystallized by the charring process. This pyrolytic fracturing and subsequent exposure to the distillate was accompanied by a steady loss of sugars from the cellulose and hemicellulose fractions of the oak cask. Distinct layers of structural degradation and product release from within the barrel stave are formed over time as the distillate expands into and contracts from the barrel staves. This complex, wood-sugar release process is likely associated with the time-dependent generation of the unique palate of bourbon whiskey.