How Bourbon Is Made

Bourbon is a strictly defined American whiskey: at least 51% corn in the mash, aged in new charred American oak barrels, distilled to no more than 160 proof, and entered into the barrel at no more than 125 proof. Within those rules there's enormous variation. Here's the process from grain to bottle, with the choices that make one bourbon taste different from another.

Step 1: The mash bill

Bourbon's defining ingredient is corn — at least 51% by law. The other 49% is up to the distiller, but it's almost always some combination of rye and malted barley. The mash bill (the recipe of grains) shapes the finished spirit's character:

• High-corn bourbons (75%+ corn) are softer, sweeter, more vanilla-forward.
• High-rye bourbons (20%+ rye) are spicier, drier, more peppery on the finish. This is the camp our Zanja-Madre Bourbon sits in.
• Wheated bourbons use wheat instead of rye in the secondary grain — softer and rounder. Maker's Mark and Pappy Van Winkle are the famous examples.

Step 2: Mashing and fermentation

The grains are cooked with water in a mash tun to convert starches to fermentable sugars. The mash is cooled, malt enzymes break the sugars down further, and yeast is pitched into the fermenters. Over three to seven days, fermentation produces a low-proof beer (around 8–10% ABV) called "distiller's beer."

Step 3: Distillation

The distiller's beer is run through a still. Most American bourbon producers use a column still followed by a pot still (called a "doubler" or "thumper"); craft producers often use just a pot still. The distillate comes off at no more than 160 proof (80% ABV). Most distillers cut at around 130–140 proof to keep more flavor in the spirit.

Step 4: Barreling and aging

This is where bourbon becomes bourbon. The clear distillate (called "white dog" or "new make") is cut to 125 proof or less and entered into new charred American white oak barrels. The new oak rule is what gives bourbon its color and most of its flavor: vanilla, caramel, brown sugar, baking spices. "Charred" means the barrels are toasted and then literally set on fire briefly to caramelize the wood sugars and create a layer of activated carbon inside.

Aging time varies. Two years is the legal minimum for "straight bourbon." Most premium bourbons age four to eight years. Beyond about twelve years, the oak starts to dominate the spirit, which is why very old bourbons can taste woody. Climate matters too — California bourbons age faster than Kentucky bourbons because of the heat.

Step 5: Bottling

After aging, the barrels are dumped, sometimes blended (mixing barrels from different parts of the rickhouse for consistency, or selecting single barrels for premium releases), filtered, and cut to bottle proof — typically 80–100 proof, sometimes higher for cask-strength releases.

Why any of this matters

Bourbon's flavor isn't an accident. Every step — mash bill, fermentation length, still cuts, char level, barrel size, warehouse position, aging time — is a deliberate choice. When you taste a bourbon you love, you're tasting the cumulative effect of dozens of decisions a distiller made years before the bottle landed in your hand.

Where to next

Try our Zanja-Madre Bourbon, learn the difference between bourbon and rye, or book a tour to see it being made.