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How is Bourbon Made? Behind The Bourbon Distillation Process

Bourbon Casks
Bourbon Casks

Bourbon is a special type of whiskey that is a product of the United States. Creating this whiskey requires distillers to follow a bourbon distilling process based on specific legal requirements by the Federal Standards of Identity. These requirements involve the mash bill, alcohol content, barreling, and additives. The rules are given below:

  • The whiskey needs to be produced in the US only

  • The grain mash should consist of 51% corn

  • The spirit should be at 160 proof (80% ABV)

  • The spirit should not be at more than 125 proof when entering the barrel

  • The spirit should use new charred oak barrels to age

  • The bottled whiskey should be at a minimum of 80 proof (40% ABV)

Although millions of people enjoy bourbon all over the world, these specific criteria remain common in the bourbon distilling process in every distillery.

How Bourbon is Made

Distillers craft bourbon through a multi-step process, which entails determining the mash bill, fermentation, distilling, and aging. Let’s take a look at them.

Determining the Mash Bill

The master distiller first creates a recipe for the mash bill by selecting different grains and their percentage for crafting bourbon. Each grain adds a unique flavor and nuance to bourbon, which results in its characteristic taste. It is up to the master distiller to create a mash bill that will result in the desired flavor and texture of the bourbon.

Grain Selection

According to the American Bourbon Association, bourbon produced in the US should comprise at least 51 percent corn. The rest of the mixture can contain a single type of grain or a mixture of grains.

Most distillers use about 60 to 80 percent corn; the rest of the ingredients can be malted barley and rye and/or wheat. A single distillery may use various combinations and proportions of grains to produce several types of bourbon with their own distinct flavor and characteristics.


Typically, all types of bourbon consist of malted barley. However, distillers may malt other types of grain as well. This process helps convert the starches in the grain into sugar that lends bourbon its mellow sweetness. It also releases enzymes that help in the fermentation process.

The first step in malting cereal is called steeping. The distillers do this by increasing the grain’s moisture content by submerging it in water. The cereal is then dried on grain beds and placed in a well-ventilated area. Once the grain starts to sprout, the distillers place it in a kiln to dry out. The high temperature in the kiln is responsible for producing the bourbon’s dark caramel-brown color.

Milling the Grain

Before grinding the grains, the distillers first subject them to a de-stoning process. This removes the stones and rocks, which can damage the grinding machines. The distillers then send the corn to a milling machine where it is ground down to release the starches. The other grains are also sent to separate batches and ground down and stored temporarily in separate containers.

Distillers will send the unmalted grain like corn to milling machines with a rotating hammer for pounding. For malted grains, distillers will use roller mills, which will gently crush the cereal. This opens up the husks and breaks down the starchy enzymes. Distillers may grind the grain three to four times to achieve the perfect consistency for bourbon fermentation.


The distillers will add grains for the mash bill to a vat of water and yeast. This mixture is heated at various temperatures and pressures to ensure all the ingredients combine well. Distillers agitate the mash with paddles throughout the cooking process, which can take anywhere between 30 and 60 minutes.

Unmalted corn needs to cook longer at a higher temperature. Distillers later lower the temperature and add the other grains. Since malted barley converts starch into sugars most efficiently, distillers will add it last and cook it for a short amount of time at lower temperatures.

The last step of the mashing process involves rinsing the spent grain to ensure the maximum release of sugars. The mash is cooled to between 77 and 86 degrees Fahrenheit and then undergoes the fermentation process.

The type of yeast and water used in the mashing process can also affect the taste of the bourbon.

There is a popular opinion that only limestone water is used to make bourbon. That’s because limestone has a high pH value, which helps in the fermentation and filtering process. However, bourbon distilleries can open up anywhere in the US and can use plain, purified water to craft bourbon.


The process of fermentation is what turns the mashed grain into alcohol. The choice of yeast is vital in the bourbon distilling process. Different types of yeast react differently with different grains, based on the specific conditions of fermentation. This affects the taste and other characteristics of bourbon. As such, many distilleries keep their own proprietary yeast cultures.

For bourbon fermentation, distillers use the entire mash, along with the sold. This technique is different from whiskey production, which uses only the starchy liquid, or the wort, during fermentation.

Distillers add more yeast to the mix along with the sour mash, also called stillage. This is the leftover mash from a previous distillation, which is added to retard bacterial growth.

The fermentation process takes about three days. During this time, the yeast turns the sugars into ethanol. The resulting viscous liquid is called distiller’s beer and has an alcohol content of up to 9.5 percent ABV.

Some distillers allow a few more days for fermentation, which raises the alcoholic content to up to 11 percent ABV. The distiller’s beer is then poured into a beer well. This beer is then constantly supplied through column stills and distilled into a clear spirit, called white dog.

Large Copper Container for Whiskey


Once the fermentation process is completed, the distiller’s beer needs to undergo the bourbon distilling process. This is crucial to get rid of impurities like carbon dioxide and toxic congeners, which are responsible for hangovers.

The bourbon distilling process will get rid of these toxic compounds, retain the good components, and increase the alcoholic content. Usually, distillers will put the bourbon through two distilling processes. One is distillation in the column stills and the other is distillation in heated copper pot stills.

Distillation Through Column Stills

The bourbon distilling process begins when the distiller’s beer is run through the stills and flows toward a heat source. This heats up the beer, evaporates the liquid, and allows the vapors to go through stripping plates. Some beer is left behind as condensation, which turns into vapors from the continuous heat.

During this process, the congeners and the fusel oils are removed from the fermentation. This increases the spirit’s purity. The tallest still can turn out a whiskey with an alcoholic content of 190 proof. However, bourbon must not be distilled to more than 160 proof as the increased alcohol content can affect its taste.

Distillation Through Copper Pot Stills

Once the distiller considers the spirit pure enough, they will allow it to flow into heated copper pot stills for another round of distillation. At this stage, sulfur and other harmful compounds will be removed from the spirit. This will improve the flavor and alcohol quality of the whiskey.

After the distillation process, the vapor will be turned into a liquid state via condensation. This is the white dog, a raw spirit. Distillers then pump this whiskey into storage tanks for barreling.

The Aging Process

Once the bourbon reaches between 80 and 125 proof, distillers pour it into new charred oak barrels for aging. The char caramelizes the sugars in the wood, which the whiskey absorbs, giving bourbon its distinctive sweet taste. The char also gives a rich amber tone to the barrels.

The barrels are stoppered with walnut corks and moved to different locations in a warehouse. During the aging process, distillers may move these barrels to different areas because of the variation in temperatures.

The federal law does not give a minimum age requirement for how long the bourbon must be aged. Whiskey aged for just three months is bourbon, though to label it straight bourbon, distillers need to age it for a minimum of two years. Bottled-in-bond bourbon is aged for at least four years and is considered premium quality.

During the barreling process, distillers will store the bourbon casks in warehouses with four or five levels. The top levels experience higher temperatures, while the lower levels have cooler temperatures. This difference in temperatures is responsible for maturing each cask differently. Distillers can choose to rotate the location of each cask throughout the aging period or blend various casks together to get the desired bourbon consistency.


The last step of the bourbon distilling process is bottling. The master distiller will check each barrel during the aging process and may taste the bourbon from time to time. The distillery will take the cork out from the barrel and pour the whiskey into a filtered through. They will add more water to the alcohol to adjust its alcoholic content to at least 80 proof.

The filter installed on the trough removes any barrel shavings or husk and allows only the liquid to go through.

The liquid is then fed into a retention tank where it is sent to a machined bottling line.

The bourbon is now ready for the store.

Bottom Line

Distilleries need to take a lot of careful steps when it comes to the bourbon distilling process. All bourbon undergoes this specific process. However, they each have their unique taste profiles.


Mar 05, 2023

Thanks for the article!


Mar 05, 2023

interesting article!


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