Bourbon · Mash Bill
What grains are in bourbon?
Only one grain is actually required in bourbon: corn, which U.S. law says has to make up at least 51% of the bill. Everything else is a choice. The distiller fills out the rest with a smaller amount of one or two flavoring grains, usually rye or wheat, plus a little malted barley. And that one choice, rye or wheat, is enough to split bourbon into styles that taste nothing alike, which is why two bottles built on the very same corn base can land on completely opposite ends of the shelf.
Why does corn have to be at least 51%?
The 51% corn floor is a legal line, not a stylistic one. Under U.S. federal rules (27 CFR), a whiskey isn't bourbon at all unless corn is the majority grain. Drop below 51% and you've made some other kind of whiskey. Corn is what supplies bourbon's base sweetness, the broad, rounded note that sits underneath everything else, so the law locks in the spirit's character before the barrel ever touches it.
Most bourbons sit well above the minimum. A typical bill runs around 70% corn, and plenty go higher. The 51% figure is the threshold a distiller has to clear, not the target they aim for, which is why the corn flavor tends to dominate even in bourbons that lean hard on their other grains.
Did you know? There's no legal upper limit short of 80% corn. At 80% or more, the spirit stops being bourbon and becomes "corn whiskey," a separate legal category with its own rules.
What do rye, wheat, and barley actually do?
Once the corn requirement is met, the distiller chooses what fills the rest of the bill. The three grains on the table each pull the spirit in a different direction.
Rye adds spice. It brings a dry, peppery edge that cuts against the corn's sweetness, which is why high-rye bourbons taste sharper and more assertive.
Wheat does the opposite. It softens and rounds the spirit, taking the edges off rather than adding them, so a wheated bourbon reads as gentler and more mellow than a rye-heavy one.
Malted barley is in the mix for a more practical reason. "Malted" means the barley has been sprouted and then dried, and that sprouting wakes up natural enzymes inside the grain. Those enzymes are what convert the starches in all the grains into the sugars that yeast can ferment into alcohol. Without that small malted-barley contribution, the rest of the mash has a much harder time turning into something you can distill. It earns its spot through chemistry more than flavor, though it does lend a faint nutty, biscuit note of its own.
| Grain | Typical role | What it adds to flavor |
|---|---|---|
| Corn | Base grain, required (≥51%) | Broad, rounded sweetness |
| Rye | Flavoring grain | Spice, dry peppery edge |
| Wheat | Flavoring grain | Softness, rounds the spirit out |
| Malted barley | Enzymes, starch conversion | Faint nutty, biscuit note |
What's a typical bourbon mash bill?
A mash bill is the recipe of grains, given as percentages. A common "traditional" bourbon runs roughly 70 to 75% corn, 10 to 15% rye, and 10 to 12% malted barley. A wheated bourbon keeps the corn and barley about the same but swaps the rye out for wheat at a similar proportion.
These are typical ranges, not fixed rules. The exact split is each distillery's own recipe, and a few percentage points in either direction is part of what gives one producer's bourbon a different personality from the next. If you want the term itself unpacked rather than just the numbers, the recipe of grains a distiller works from is worth understanding on its own.
What are high-rye, wheated, and four-grain bourbons?
The named sub-styles all come from that single flavoring-grain choice. A high-rye bourbon pushes the rye up, often to around 18% or more, for extra spice and bite. A wheated bourbon replaces the rye with wheat entirely, producing the softer, rounder profile that style is known for. That mellow character a wheat-based bill produces is the whole reason a distiller would choose wheat in the first place.
A four-grain bourbon does something different. Instead of choosing between rye and wheat, it uses both, putting corn, rye, wheat, and malted barley all in one mash. The result tries to carry the spice of rye and the softness of wheat at the same time.
This is where two bourbons built on the same corn base go their separate ways. The corn is locked in by law, so the character that distinguishes one bourbon from another comes down to which flavoring grain the distiller reaches for. The grain bill, not the barrel alone, is where a bourbon's personality starts.