Bourbon Whiskey
American corn-forward whiskey aged in new charred oak — defined by US federal law since 1964.
Bourbon whiskey is an American spirit distilled from a grain mash containing at least 51% corn, aged in new charred oak containers, and distilled to no more than 80% ABV. Federal Standards of Identity (27 CFR Part 5) define bourbon in law; the spirit must be produced in the United States (not exclusively Kentucky, despite common belief). Key flavour compounds include vanillin, lactones, and caramel notes derived from the charred oak interaction during ageing. The major bourbon-producing states are Kentucky (accounting for approximately 95% of production) and Tennessee (which requires the Lincoln County Process charcoal filtration distinguishing Tennessee whiskey from bourbon).
Quick facts
- Type
- Spirit Base
- Base spirits
- bourbon
- Era
- late 18th century–present
- Origin
- Kentucky, United States
- Glass
- old-fashioned
- IBA listed
- No
Federal Definition and Grain Bill
The US Federal Standards of Identity for bourbon (27 CFR 5.22(b)(1)) establish the following requirements: produced in the United States; made from a grain mixture containing at least 51% corn; distilled at no more than 160 proof (80% ABV); stored in charred new oak containers; entered into the barrel at no more than 125 proof (62.5% ABV); bottled at no less than 80 proof (40% ABV). 'Straight bourbon' additionally requires ageing for at least two years and prohibits colouring agents. 'Kentucky Straight Bourbon' must be produced in Kentucky. The corn requirement is met by a variety of grain bills: a typical bourbon may be 65–80% corn, 10–20% malted barley (for enzymes to convert starches to fermentable sugars), and 5–15% rye or wheat. 'Wheated bourbon' (Maker's Mark, W.L. Weller) substitutes wheat for rye, producing a softer, sweeter flavour.
Charred New Oak and Flavour Development
The requirement for new charred oak containers (rather than used barrels) is the defining technical constraint of bourbon production and its primary source of flavour differentiation from other whiskey styles. Charring the interior of a white oak barrel (typically American white oak, Quercus alba) at temperatures of 200–260°C creates three distinct zones: a layer of carbon (the 'red layer') that acts as a filter; a caramelised sugar layer that contributes vanilla, caramel, and toffee compounds; and the deeper wood that contributes oak lactones, tannins, and lignin-derived vanilla. The spirit entering the barrel at 62.5% ABV expands and contracts with temperature changes (Kentucky's climate produces a pronounced annual cycle), drawing liquid in and out of the wood pores. Standard ageing is 2–23 years; most popular bourbons are 4–12 years old.
Sources & further reading (1)
- encyclopedia — accessed 2026-05-08
Frequently asked questions
Is all bourbon made in Kentucky?
No. The US federal definition requires only that bourbon be produced in the United States, not specifically Kentucky. Bourbon is produced in many US states including Texas, Colorado, New York, and others. However, Kentucky accounts for approximately 95% of US bourbon production by volume, and the Kentucky climate (hot summers, cold winters) is considered optimal for the rapid barrel cycling that accelerates flavour development. Some bourbon regulations define 'Kentucky Bourbon' or 'Kentucky Straight Bourbon' as a geographic designation.
What is the difference between bourbon and Tennessee whiskey?
Tennessee whiskey meets all the requirements for bourbon but undergoes an additional step called the Lincoln County Process: the distillate is filtered through or steeped with sugar maple charcoal before barreling. This process is credited with removing certain congeners and adding a specific mellowness. Tennessee law (passed 2013) requires Tennessee whiskey to use the Lincoln County Process, be produced in Tennessee, and use at least 51% corn. Jack Daniel's and George Dickel are the major Tennessee whiskey producers.