Bourbon is whiskey that meets a specific set of legal requirements defined by U.S. federal regulations. At minimum, it must be made from at least 51% corn, distilled to no more than 160 proof, aged in new charred oak barrels at no more than 125 proof entry, bottled at 80 proof or higher, and produced in the United States. Miss any one of those rules and you can’t put “bourbon” on the label.
The Six Legal Requirements
Title 27 of the Code of Federal Regulations spells out every requirement. Here’s what a whiskey needs to qualify as bourbon:
- At least 51% corn in the mash bill. The grain mixture fermented to make bourbon must be majority corn. The remaining 49% typically includes rye or wheat as a flavoring grain, plus malted barley, which provides enzymes that help convert starches to sugars during fermentation.
- Distilled at 160 proof or less (80% alcohol by volume). This ceiling preserves more of the grain’s character in the spirit. Distill higher and you strip away flavor, pushing the product closer to neutral grain spirit.
- Entered into the barrel at 125 proof or less (62.5% ABV). Before 1962, distillers experimented with various entry proofs. The 125-proof cap was locked in that year. Prior to Prohibition, entry proof was generally much lower, around 107.
- Aged in new, charred oak containers. Almost always a standard 53-gallon barrel. The wood cannot be reused from a previous fill, and it must be charred, not just toasted. No minimum aging period is required for basic bourbon.
- Bottled at 80 proof or higher (40% ABV).
- Made in the United States. Federal regulations explicitly state that the word “bourbon” may not describe any whiskey not distilled and aged in the U.S.
Bourbon Does Not Have to Come From Kentucky
This is one of the most common misconceptions. Bourbon can legally be made in any U.S. state. What is restricted is the label “Kentucky Straight Bourbon Whiskey,” which can only appear on bourbon actually produced in Kentucky. That distinction comes from federal rules treating “Kentucky” the same way “Cognac” is treated for brandy: it’s a geographic name tied to a specific place, not a generic style term. So a distillery in Texas or New York can absolutely make bourbon. It just can’t call it Kentucky bourbon.
No Additives Allowed
This is where bourbon parts company with most other whiskeys worldwide. Bourbon cannot contain added coloring, flavoring, or blending materials. If a producer adds caramel coloring to straight bourbon, the product legally stops being straight bourbon whiskey and must be relabeled as a distilled spirits specialty with the additive disclosed. Scotch, Canadian whisky, and many other global whiskeys routinely add caramel coloring for batch-to-batch consistency. Bourbon’s color comes entirely from the interaction between spirit and wood.
Other types of American whiskey, like blended whiskey, are allowed to include caramel and blending sherry as long as those additions don’t exceed 2.5% of the final volume. Bourbon gets no such allowance.
What “Straight” Means on the Label
Plain bourbon has no minimum aging requirement. “Straight bourbon” does: it must be aged at least two years. If a straight bourbon has been aged fewer than four years, the label must include a specific age statement. Once it hits four years or older, the age statement becomes optional, which is why many bottles on shelves don’t list an age at all.
Straight bourbon also carries the same ban on additives. The combination of mandatory aging and zero additives is why many bourbon drinkers specifically look for the word “straight” on the label.
Bottled in Bond: A Higher Standard
The Bottled-in-Bond Act of 1897 created an even stricter tier. To earn this designation, bourbon must meet all the standard bourbon rules plus several more:
- Produced in a single distilling season at a single distillery
- Aged at least four years
- Bottled at exactly 100 proof (50% ABV)
- The label must identify the distillery where it was made, and the bottling location if different
Bottled-in-bond was originally a consumer protection measure in an era when adulterated whiskey was common. Today it functions as a quality signal, telling you exactly where, when, and how the spirit was produced.
Why New Charred Oak Matters So Much
The requirement for new charred oak barrels is arguably the single biggest factor separating bourbon’s flavor from other whiskeys. Scotch and Irish whiskey typically age in used barrels, often the same barrels bourbon already spent time in. A fresh, charred barrel is far more reactive. The charring caramelizes sugars in the wood and breaks down a structural compound called lignin into vanillin, the same molecule responsible for vanilla flavor. That’s why vanilla is one of bourbon’s most recognizable tasting notes.
The wood also contributes compounds called oak lactones, which in their combined forms produce a subtle coconut character. Deeper layers of the barrel release tannins and other compounds that create the caramel, toffee, and spice notes people associate with bourbon. Because the barrel is always new and always charred, bourbon picks up these flavors faster and more intensely than whiskeys aged in used cooperage.
The Role of Corn and Secondary Grains
The 51% corn minimum gives bourbon its characteristic sweetness. Many producers use 60% to 75% corn, and a few go even higher. The remaining grains shape the bourbon’s personality. Rye as the secondary grain adds spice and a drier, more peppery finish. Wheat in that role produces a softer, rounder spirit. Malted barley almost always makes up a portion of the mash bill because its enzymes are essential for breaking down starches into fermentable sugars.
A bourbon made with rye as the secondary grain is sometimes called a “high-rye bourbon” when the rye percentage is notably above average, while bourbons using wheat instead are often called “wheated bourbons.” Both are still bourbon. The corn majority is what qualifies them; the secondary grains are what differentiate them on the shelf.
Sour Mash: Standard but Not Required
Nearly every major bourbon producer uses a process called sour mash, though it’s not legally required. This involves adding a portion of previously fermented mash, called backset, into a new batch. The backset lowers the pH of the new mash, creating a slightly acidic environment that supports healthy yeast growth and limits bacterial contamination. The result is more consistent fermentation from batch to batch. It’s essentially the bourbon equivalent of a sourdough starter: using material from the last batch to inoculate the next one.
Some smaller producers use a “sweet mash” method, starting each batch with entirely fresh ingredients and no backset. This introduces more variability between batches, which some craft distillers see as a feature rather than a flaw.