Seven distinct stages transform raw grain into the amber liquid that ends up in your glass. Each step has been refined over two centuries of craft and science.
The mash bill is the distiller's signature. Corn provides sweet body; rye adds spice and dryness; wheat delivers softness and floral notes; malted barley provides the enzymes that convert starches to fermentable sugars.
Typical ratios: 65–80% corn, 5–20% rye or wheat, 5–15% malted barley
Grains are hammer-milled to break them open, then cooked with hot water in large cookers. Corn is added first at high heat, then temperature is dropped to add rye/wheat, then barley. The "setback" — spent liquid from a previous distillation — is often added for pH control.
Sour mash: recycled backset keeps fermentation consistent batch to batch
Yeast is added to the cooled mash in massive cypress wood or stainless tanks. Over three to five days, yeast converts sugars to alcohol, CO₂, and hundreds of congener compounds that will become flavor. The result — "distiller's beer" — is around 6–8% ABV.
Yeast strain is each distillery's most guarded secret, often maintained for generations
The beer runs through a column still to produce "low wine" around 55–70% ABV, then through a "doubler" or "thumper" pot still to reach final distillate strength. The distiller makes "cuts" — selecting only the heart of the run, discarding the harsh heads and tails.
The clear, unaged spirit is called "white dog" or "new make" — fiery and raw
New American white oak barrels — typically 53 gallons — are charred on the inside. Char levels range from #1 (light caramelization) to #4 "alligator" (deep cracking char). The char creates a "red layer" just below the surface: a filter of caramelized sugars that strips sulfur while imparting vanilla and caramel.
A single barrel holds roughly 200 bottles at bottling strength
Barrels are stacked in unheated, uninsulated rickhouses (aging warehouses). Kentucky's climate — blazing summers to 100°F, winters below freezing — causes barrels to expand and contract, pushing spirit deep into the wood and back out again. Upper floors run hotter, producing faster-maturing, bolder spirits.
60–70% of a bourbon's final flavor comes from the wood and the aging environment
Mature barrels are dumped and blended to achieve consistent flavor profiles, or bottled as single barrels. Proof is reduced by adding limestone-filtered Kentucky spring water. Premium bottlings are non-chill filtered to preserve oils, waxes, and fatty acids that give the liquid body and a rich "bead" in the glass.
The "angel's share" — roughly 3–5% per year evaporates through the barrel