US Standard of Identity: The U.S. Standard of Identity defines Bourbon Whiskey as a spirit which has these properties:

  • Origin: Made in the U.S.
  • Grains: At least 51% corn
  • Proof: Distilled to no more than 160” proof and barreled at no more than 125’ proof
  • Container: Stored in new, charred oak containers
  • Additives: No additives allowed except water
  • Aging: No minimum aging time
    • Straight bourbon must be aged for a minimum of 2 years. If the bourbon is less than 4 years old, than the age must be stated on the label. Bourbon can be made in any state but to be call “Kentucky Straight Bourbon” the bourbon must be made in Kentucky.
  • Grains: Bourbon is most commonly made using 4 types of grains, each of which provides different attributes to the final spirit:
    • Corn: Sweetness / Higher Starch / Great for Alcohol Yield
    • Rye: Spice / Baking Spice Notes
    • Wheat: Soft / Less Bitter Grain Notes
    • Malted Barley: Provides Enzymes / Malt Notes

Malted Barley: How is barley malted? The process for malting barley includes soaking, resting, germination and dying:

  • Soaking: The barley is soaked in water for about 24 hours
  • Resting: The barley is loaded into large vats in constant circulation to rest
  • Germination: Over about 3 weeks, the grains sprout or germinate, and the amylase enzyme is created.
  • Dried: The malting process is halted after germination by air drying in a kiln

Mashbills: A “mashbill” is the grain recipe for whiskey or bourbon. In bourbon making, there are typically 3 styles:

  • Traditional/High Corn Style: About 70-80% corn; balance divided between rye and malted barley.
  • High Rye Style: About 60-70% corn; 18% or more rye; balanced with malted barley.
  • Wheated Style: About 70-80% corn; balance divided between wheat and malted barley.

Water/ Yeast: In addition to grains, there are two other ingredients common to all Bourbons:

  • Water: About 60% of an 80 proof bottle of Bourbon is water. Distiller’s prefer iron free water. Kentucky spring water is naturally iron fee and contains only helpful minerals like dissolved limestone (calcium) which is desirable for feeding the yeast during fermentation.
  • Yeast: Yeast is essential to produce alcohol. The type of yeast chosen can enhance the flavors of the grains and is typically specially selected and safeguarded by each distiller for this reason. Bourbon makers, unlike wine or some other spirits makers like rum or tequila, do not use wild yeast.

Milling, Cooking & Mashing: Follow along with the steps in Bourbon making from Milling to Maturation below:

  • Milling: The dried grains are separately ground to exacting sizes to maximize their ability to dissolve their starches in water, while leaving behind the husks and chaff after cooking.
  • Cooking: The grains are mixed with water and then cooked. Cooking allows the starches to become soluble, dissolving them into the liquid. The last grain we add is the malted barley.
  • Mashing: This begins the Mashing process. The technical process is called saccharification—where the amylase enzymes from the malted barley convert the grain starches into fermentable sugars. After Mashing is complete, we add a portion of the previous day’s spent mash to lower the pH value to prevent spoilage and promote a consistent taste from batch to batch. The process is called the “sour Mash Process”.

Fermentation: To start fermentation, live yeast cells are added to the mash. The yeast cells consume the sugars in the mash and produce alcohol, CO2 and heat. The yeast also produces a small amount of other flavor and aroma compounds called congeners which add character to the aged spirit.

  • Entire process takes 3-5 days.
  • Once the alcohol levels reach 8-12% the yeast can no longer survive and begins to die.
  • The liquid now resembles a low alcohol beer and is know a “distiller’s beer.
  • It is this distiller’s beer that we will ferment to crate our spirit.


  • First Distillation: Distillation is the process of using heat to separate the alcohol from the distiller’s beer. Distillation works because alcohol turns to vapor at about 173° Fahrenheit which is below the boiling point of water at 212°. While not a legal requirement, Bourbon makers typically distill twice. The first distillation is frequently done in a tall column continuous or ‘beer’ still. The mash enters near the top and falls downward and meets steam rising up from the bottom. When the two come in contact, distillation occurs and the alcohol vapor rises, and the mash solids and water fall back downward. The condensed vapor from the first distillation is called ‘low wine’ and is about 125° proof.
  • Second Distillation: For the second distillation, Bourbon makers commonly use a form of pot still. The pot still reheats the low wine producing a second distillation. The vapors rise, leaving more water and impurities behind. The alcohol vapors are collected and condensed to produce the final spirit called high wine at about 160° proof. Once the high wine is cooled, it is piped into new charred oak barrels to begin the maturation process. The barrels are closed with a wooden plug called a ‘bung.’


  • Why Oak? American Oak is abundant in the U.S. and in particular in the region of Kentucky and the Ozark mountains. This makes it easy to find and less costly to acquire. From the cooper’s perspective, Oak holds liquid well. Oak contains tyloses which are globular substances which block the pores of wood staves, preventing liquid from running through them. Oak is also strong. But it can be bent into shape to make a barrel—with the application of heat. Coopers also like oak because it is able to resist insects and certain types of molds. For the bourbon distiller, the benefits are also impressive. Despite keeping liquid in tact, oak is still porous enough to allow for vapor alcohol to penetrate it from the inside, and oxygen to penetrate it from the outside. American oak is also high in vanillins and lactones which help flavor the bourbon during aging.
  • Barrel Size and Finishes: Barrel size and finishes also come into play when making bourbon. Under Federal Regulations, there is only a requirement the spirit spend some time in a new charred oak container. Nothing regulated about size. And nothing about using a process of single or double maturation. In double maturation, the first maturation is in a new charred oak container, and a second may be in a used or uncharred barrel. A used barrel may have been previously used to age wine, port, cognac, madeira or virtually anything. If the second maturation is in a used barrel, this is commonly referred to as a ‘finish’, such as, for example, a sherry finish using a used sherry barrel or a port finish using a used port barrel. Having the bourbon come into contact with the port soaked barrel adds notes from the port which will impact the taste and allow the distiller to develop a more unique flavor profile.
  • Barrel Charing: All bourbon must be aged in new charred oak barrels. To char a barrel, thenside of the barrel is literally set on fire. It can be quickly extinguished to create a level 1 ‘flash char’. Or it can be left to burn for up to 55 to 60 seconds to produce the highest level of char, level 4, which is commonly referred to as an alligator char. In fact, the burned surface of the wood looks quite like the skin of an alligator.
  • It allows the whiskey to pick up notes of toast, vanilla, smoke, clove and spice. It removes bitter flavors like sulfur. It contributes sweetness from wood sugars. And it imparts color from the same caramelized layer.

Blending / Batch Size: The varying ages of the barrels in the rackhouse, and the impact of the environment inside the rackhouse, make the craft of bourbon whiskey creation an art for a true master. It is a job only for one who understands how to blend the whiskey from different barrels into one consistent tasting product year in and year out. Almost all bourbon brands are blends of barrels of a similar product. Once blended, typically pure demineralized water is added to adjust the proof to the brand standard. No other flavors, colorings or additives may be added by law in order to be called a bourbon.

  • Small Batch Bourbon: Sometimes these batches may be hundreds of barrels, sometimes only a few. The term ‘small batch’ bourbon, while not a legal term, has gained industry usage to indicate a batch made from a more select, limited group of barrels.
  • Single Barrel Bourbon: The term single barrel indicates only one barrel’s contents are in the designated bottle. Single barrel bourbons, however, are still usually adjusted with water to the desired proof.
  • Cask-Strength Bourbon: Cask-strength or barrel-proof bottlings are bottled straight from the cask and are not cut with water. They may be filtered, but you will usually notice a difference in proof among bottles, indicating a true cask strength product.
  • Straight From The Barrel Bourbon: Lastly, you may sometimes hear of a whiskey bottled ‘Straight from the Barrel’— in which case it too has no water added—and is also unfiltered—making it as close to a barrel style whiskey as possible.

Information Provided by our Friends @ Beam Suntory, Inc.