Bourbon whiskey distilleries face many decision points when creating their own style. Although the number of distilleries is relatively small, there are many different styles and brands. These distilleries express their uniqueness through various factors, such as the grain ratio, yeast type, the amount of sour mash used, distillation strength, the intensity of the oak barrels, and the position of the barrels in the warehouse.
1. Grain Recipe
Corn provides a rich, oily sweetness. To produce bourbon whiskey, the corn content must be at least 51%. Malted barley provides enzymes to convert starch into sugar, while rye contributes spiciness and acidity. To produce straight rye whiskey, rye content must be at least 51%, with wheat adding sweetness and a more delicate texture. The ratio of corn to other grains significantly affects the final flavor of the whiskey. The higher the rye content, the spicier the final product. Distilleries often use more than one grain recipe.
2. Milling the Grains
The grains are milled separately, without mixing.
3. Water
Limestone-rich hard water contains a high amount of minerals.
4. Cooking
- A: The corn and water mixture is heated until near boiling. It is then cooked in either a pressure cooker or an open-top boiler to gelatinize the starch.
- B: Since rye and wheat tend to clump at high temperatures, they are added only after the temperature drops to 77°C (170°F). After cooking, the mixture is cooled to 63.5°C (146°F).
- C: At this point, malted barley is added to convert the starches into fermentable sugars. The mixture is then prepared for fermentation by adding two key components.
5. Backset / Sour Mash / Bottom Residue
As distillation nears completion, the leftover acidic liquid (sour mash) is added to the fermentation vat to adjust the acidity and prevent bacterial infection. The amount of sour mash added can affect the sugar content of the mash. Bourbons with a lighter style tend to use less sour mash, but every bourbon whiskey incorporates some amount of sour mash.
6. Yeast
Every distillery has its own proprietary or patented yeast strains, which are carefully guarded. The characteristics of the yeast have a significant impact on the final whiskey, promoting the development of specific congeners (flavor elements).
7. Fermentation
Fermentation typically takes up to three days, producing a beer-like liquid with an alcohol content of around 5-6% ABV.
8. Distillation
The fermented beer is distilled in a single-column still, which has perforated plates at intervals. The beer is introduced from the top, while hot steam enters from the bottom. As the beer passes through the plates, the rising steam extracts the alcohol. The alcohol is condensed into a spirit, with an alcohol content of around 55-60% ABV. The acidic residue left at the bottom of the still is the sour mash or backset.
9. Second Distillation
This step occurs in either a "thumper" (a container with water that extracts heavier elements as the alcohol vapor passes through) or a "doubler" (a simple pot still). The alcohol content of the distilled spirit is crucial to flavor development. By law, the "white dog" (new make spirit) must not exceed 80% ABV. Most distillers collect the new make spirit well below this limit, as a lower ABV yields a fuller character. With the rise of craft distilling, pot stills are also now used to produce bourbon whiskey.
9.1 Tennessee Whiskey
In Tennessee, the new make spirit is filtered through large vats of sugar maple charcoal after distillation, which removes harsh elements from the new spirit.
10. Maturation
The alcohol content of the white dog must be diluted to below 62.5% ABV. The strength of the oak barrels also affects the flavor. The whiskey must be aged in new, heavily charred oak barrels with a capacity of 200 liters.
11. Warehousing
The warehouse environment has a long-term influence on the characteristics of the whiskey. The higher the warehouse temperature, the more active the interaction between the new spirit and the oak. Conversely, in cooler environments, the interaction is slower. This means that the location of the warehouse, the number of floors, and the materials used (brick, metal, wood) are critical to flavor development. Similarly, the position of the barrels in the warehouse also affects the flavor. Some distilleries periodically rotate the barrels to achieve an even maturation; others scatter the barrels across different warehouses, while some reserve specific locations or floors in the warehouse for certain brands. By law, the maturation process must last at least two years.