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how is bourbon made

Bourbon is made by cooking a grain mash (mostly corn), fermenting it into a “beer,” distilling that beer into a clear spirit, and aging it in new charred oak barrels until it picks up color and flavor.

Quick Scoop

Here’s the short, practical version of how bourbon is made from grain to glass.

1. Mash bill: the grain recipe

  • By law, bourbon must be made from a mash that is at least 51% corn; most distilleries use around 60–75%.
  • The rest is usually malted barley plus either rye (for spice) or wheat (for a softer profile).
  • Distillers call this grain formula the “mash bill,” and each brand guards its exact proportions because they strongly shape flavor.

Think of the mash bill as the DNA of a bourbon: change the percentages, and you change the personality of the whiskey.

2. Mashing: turning starch into sugar

  • Grains are coarsely milled, then mixed with water in a cooker and heated; this thick porridge is the “mash.”
  • Corn is cooked first at higher temperatures and longer, then the heat is lowered before adding rye or wheat, and finally the more delicate malted barley.
  • Natural enzymes from the malted barley convert grain starches into fermentable sugars so yeast can later turn them into alcohol.

Some producers use a “sour mash” method, adding a portion of stillage (backset) from a previous batch to keep pH stable and flavor consistent.

3. Fermentation: making “distiller’s beer”

  • Once the mash cools to roughly 25–30 °C (77–86 °F), it is pumped into large fermenters and inoculated with distillers’ yeast.
  • Unlike some other whiskies, bourbon typically ferments the whole mash (liquid plus solids), not just a strained sugary liquid.
  • Over about 2–4 days, the yeast converts sugar into alcohol and carbon dioxide, creating a tangy, grainy “beer” at around 8–10% alcohol by volume.

At this stage it looks like murky beer and smells bready, fruity, and a bit sour—drinkable, but it’s not bourbon yet.

4. Distillation: concentrating flavor and alcohol

  • The fermented mash (“distiller’s beer”) is pumped into a tall column still where steam rises from below and alcohol-rich vapor is separated from the grainy liquid.
  • This first pass produces a low-strength spirit often around 120–125 proof, sometimes called “low wines.”
  • Many bourbon makers then run it through a second still (a doubler or thumper) to reach a cleaner, “high wine” that is still legally under 160 proof so grain flavors remain.

The clear spirit that comes out of this process is often called “white dog” or “new make” and tastes hot, grainy, and raw compared with the finished bourbon.

5. Barreling: into new charred oak

  • By law, bourbon must be aged in new, charred barrels made from American white oak.
  • The fresh spirit is diluted with water so it enters the barrel at no more than 125 proof (62.5% ABV).
  • Inside the barrel, the charred layer acts like a filter, while the toasted wood beneath contributes caramel, vanilla, spice, and color as the spirit soaks in and out of the oak.

Producers often use standard 53-gallon barrels, but where they store them in the warehouse (hot upper floors vs cooler lower ones) changes how intense and fast the maturation feels.

6. Aging: time, wood, and climate

  • There’s no minimum aging for plain bourbon, but “straight” bourbon must be aged at least 2 years, and many popular bottlings sit for 4–8 years or more.
  • Seasonal temperature swings cause the whiskey to expand into the oak when it’s hot and retreat when it’s cool, pulling out more flavor compounds over time.
  • Each barrel ages a little differently, so distilleries taste and track them until they decide a barrel or group of barrels has reached the target character.

This is why you see labels like “single barrel” (one distinctive barrel) or “small batch” (a limited set of barrels blended for a particular profile).

7. Filtering, proofing, and bottling

  • Mature bourbon is emptied from barrels and filtered to remove bits of char before bottling.
  • It’s usually diluted with water down to a drinkable strength of at least 80 proof (40% ABV), unless it is sold as “cask strength” at the natural barrel proof.
  • To legally be called bourbon, producers are not allowed to add flavorings or color; the taste and color must come from the grains, fermentation, distillation, and barrel alone.

From there, it’s bottled, labeled, and shipped off to shelves, where different mash bills, aging times, and blending choices give you everything from sweet, mellow bourbons to bold, spicy ones.

Information gathered from public forums or data available on the internet and portrayed here.