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Decoding the Magic: How Do They Make Bourbon?

a bottle and a glass of bourbon

Last Updated on November 5, 2023 by Lydia Martin

Get ready to uncover the captivating process behind the creation of bourbon as we dive into the question: How do they make bourbon? 

Join me on an intriguing exploration where we’ll unravel the artistry and craftsmanship that goes into each batch of this iconic American spirit.

From carefully selected grains to the magical alchemy of aging in charred oak barrels, we’ll unveil the secrets that make bourbon a true sensory delight. 

So, grab a glass and prepare to be enchanted as we embark on a journey through the fascinating world of bourbon production. Let’s unveil the mystique of how do they make bourbon, sip by sip.

Table of Contents

Introduction

three shots of bourbon

What is bourbon?

Bourbon is a type of whiskey that is distinctively American. Many attribute the name “bourbon” to its association with Bourbon County, Kentucky, which is the birthplace of this esteemed spirit. It is estimated that approximately 95 percent of all bourbon production takes place in this region.

It is made primarily from fermented corn mash and aged in charred oak barrels. Bourbon production is regulated by law in terms of its ingredients and the aging process. To be legally labeled as bourbon in the United States, the following criteria must be met [1]:

  • Mash Composition: Bourbon must be from a grain mixture of at least 51% corn. The remaining percentage typically includes other grains like malted barley, rye, or wheat.
  • Distillation Process: The distillation of bourbon involves a copper still, where the fermented mash is heated to separate alcohol from the mixture. The distillate, or “white dog,” is collected for further processing.
  • Aging: Bourbon must be aged in new, charred oak barrels. The law requires these barrels to be made of charred American oak, which imparts flavors and colors to the spirit during aging.
  • Aging Duration: Bourbon must be aged for at least two years in the United States to be labeled as “straight bourbon.” However, if it is aged for less than four years, the label must disclose the duration of aging.

Ingredients

a shelf of bourbon with cool lighting

Primary grain

What is the primary grain used in bourbon?

The primary grain used in bourbon production is corn. According to U.S. law, bourbon must have a grain mixture of at least 51% corn.

This high corn content distinguishes bourbon from other types of whiskey, such as rye or malt.

Why is this grain chosen?

Corn is chosen as the primary grain in bourbon for several reasons:

  • Flavor profile: Corn imparts a distinct sweetness to the bourbon. It contributes to the rich, smooth, and slightly sweet taste that is characteristic of bourbon.
  • Abundance and affordability: Corn is widely available and relatively inexpensive, making it a practical choice for large-scale bourbon production.
  • Tradition and heritage: Corn has been a staple crop in the United States, particularly in the southern states where bourbon production has strong historical roots. Using corn as the primary grain reflects bourbon’s tradition and cultural significance as an American spirit.

Secondary grains

What are the secondary grains used in bourbon?

Secondary grains commonly used in bourbon production include rye, barley, and wheat. The specific combination of secondary grains varies among bourbon producers and can significantly impact the flavor profile.

What role do these grains play in bourbon production?

In making bourbon, secondary grains play a crucial role in shaping the flavor profile and character of the spirit. Let’s explore the significance of each of these grains:

  • Rye: Rye adds spice and complexity to the flavor profile of bourbon. It contributes notes of pepper, spice, and a slight dryness. Bourbons with higher rye content tend to have a spicier and more robust character.
  • Barley: Barley is primarily used for its enzymatic properties. It contains enzymes that convert starches into fermentable sugars during the mashing process, aiding in the fermentation of the grains. Additionally, barley can contribute some malty and nutty flavors to the bourbon.
  • Wheat: Wheat is chosen for its smoothness and mellowing effect. Bourbons with a higher wheat content tend to have a softer, sweeter, and smoother profile. Wheat can contribute flavors like caramel and vanilla, enhancing the overall sweetness of the bourbon.

Water

How is water used in bourbon production?

Water is a crucial ingredient in bourbon production and is used at various stages throughout the process. Its primary uses include:

  • Mash preparation: Water is mixed with the grains during the mashing process to convert starches into fermentable sugars.
  • Fermentation: Water is added to the mash to adjust the consistency and provide the necessary environment for yeast fermentation.
  • Proofing: Water is added to the distilled bourbon to reduce alcohol content to the desired proof before bottling.

What are the requirements for water used in bourbon production?

The quality of water used in bourbon production is essential. Some requirements for water include:

  • Purity: Water should be free from impurities and contaminants that could negatively impact the taste or quality of the bourbon.
  • Mineral content: Certain minerals in water can contribute to flavor development during fermentation and aging. The specific mineral composition of the water used can influence the character of the final product.
  • Consistency: Consistency in water quality is vital to ensure consistency in the production process and the final flavor profile of the bourbon.
  • Bourbon distilleries often take great care in sourcing water that meets these requirements, ensuring its suitability for producing high-quality bourbon.

Mash Preparation

Milling

What is the purpose of milling?

Milling serves the crucial purpose of breaking down the grains used in bourbon production into smaller particles. The main objectives of milling are:

  • Exposing starches: Milling exposes the starches in the grains, making them more accessible for conversion into fermentable sugars during the mashing process.
  • Enhancing extraction: By increasing the surface area of the grains, milling facilitates the extraction of flavors, sugars, and enzymes during subsequent steps, ensuring a more efficient and effective mashing process.

How is the grain milled in bourbon production?

Bourbon producers utilize various milling techniques, including roller mills or hammer mills, to achieve the desired particle size.

Roller mills consist of multiple pairs of rollers that crush the grains, while hammer mills utilize rotating hammers to pulverize the grains. 

The specific method chosen depends on the distillery’s equipment and desired characteristics of the milled grain.

The objective is to achieve a consistent and uniform particle size that balances efficient extraction and optimal starch exposure.

Cooking

Why is cooking necessary in bourbon production?

Cooking, also known as mashing or steeping, is a crucial step in bourbon production that serves several important purposes:

  • Gelatinization: Cooking the milled grains allows the starches within them to undergo gelatinization, a process in which the starch granules absorb water and swell. This gelatinization process makes the starches more accessible for enzymatic conversion during fermentation.
  • Enzyme activation: Cooking activates natural enzymes present in the grains, particularly those found in barley, that facilitate the breakdown of complex carbohydrates into fermentable sugars.
  • Flavor extraction: Cooking the grains in hot water helps extract flavors, aromas, and other desirable compounds from the grains, contributing to the overall flavor profile of the bourbon.
  • Sanitization: Cooking the mash at high temperatures helps eliminate unwanted bacteria or microorganisms, ensuring a clean and healthy fermentation process.

What is the process of cooking the mash?

The process of cooking the mash involves the following steps:

  • Grain mixing: The milled grains, including the primary grain (such as corn) and secondary grains (such as rye, barley, or wheat), are mixed together in the desired proportions.
  • Cooking vessel: The grain mixture is transferred to a cooking vessel, often a large, steam-jacketed mash cooker or cooker/steamer combination.
  • Hot water addition: Hot water is added to the cooking vessel, covering the grain mixture, typically at temperatures ranging from 150°F to 180°F (65°C to 82°C). The specific temperature and water-to-grain ratio depend on the distillery’s recipe and desired outcome.
  • Cooking duration: The mash is cooked for a specific duration, typically ranging from 30 minutes to 2 hours. This allows for the gelatinization of starches and the extraction of flavors and sugars.
  • Stirring and monitoring: During cooking, the mash is stirred periodically to ensure even heat distribution and prevent the grains from clumping together. The temperature is closely monitored to maintain the desired range throughout cooking.
  • Cooling: After cooking, the mash is cooled down to a temperature suitable for yeast fermentation, usually around 90°F (32°C).

The cooking process sets the foundation for the subsequent steps in bourbon production, providing a well-prepared mash rich in fermentable sugars, flavors, and enzymes necessary for yeast activity and developing the desired bourbon characteristics.

Fermentation

Yeast

What role does yeast play in bourbon production?

Yeast is a crucial component in bourbon whiskey production as it plays a fundamental role in fermentation. 

Yeast is responsible for converting the sugars present in the mash into alcohol, specifically ethanol and carbon dioxide, through a process called fermentation. 

Without yeast, the conversion of sugars into alcohol would not occur, and bourbon production would not be possible.

What types of yeast are used in bourbon fermentation?

Two primary types of yeast are used in bourbon fermentation: distiller’s yeast and wild yeast.

Distiller’s yeast

Distiller’s yeast is a cultivated strain of Saccharomyces cerevisiae that has been specifically selected for its ability to thrive in the conditions of bourbon fermentation.

It is chosen for its consistent performance, efficiency in converting sugars, and ability to produce desirable flavor compounds during fermentation.

Wild yeast

Some bourbon producers prefer to incorporate wild yeast strains naturally present in the distillery environment.

Wild yeast strains can contribute unique flavors and characteristics to the fermentation process, adding complexity to the final bourbon product.

However, wild yeast can be less predictable than cultivated yeast strains, as they may introduce more variation and require careful monitoring and management.

Fermentation process

How is the mash fermented?

The fermentation process in bourbon production involves the following steps:

  • Yeast addition: After the mash has been cooked and cooled, the yeast is added to the mash. This process can utilize a technique called “sour mash,” where a portion of the previously fermented mash, known as “backset,” is added to the new mash. The yeast ferments the sugars present in the mash, converting them into alcohol and carbon dioxide.
  • Fermentation vessel: The mash, now known as the “wash,” is transferred to a fermentation vessel, typically made of stainless steel or wood. The vessel is designed to allow the release of carbon dioxide produced during fermentation while preventing contamination.
  • Fermentation conditions: The fermentation vessel is maintained at a controlled temperature, typically between 80°F and 95°F (27°C to 35°C). This temperature range is ideal for yeast activity and encourages the production of desirable flavors and aromas.
  • Fermentation duration: The fermentation process typically lasts three to seven days, although it can vary depending on the distillery’s recipe and desired outcome. During this time, the yeast consumes the sugars in the mash, producing alcohol and other byproducts.
  • Monitoring and management: The fermentation process is closely monitored to ensure that the yeast is active and progressing as intended. Distillers may monitor factors such as pH levels, temperature, and the production of specific compounds to guide the fermentation process and maintain consistency.

How long does the fermentation process typically take?

The fermentation process in bourbon production usually takes between three and seven days, although some distilleries may opt for longer fermentation periods. 

The duration of fermentation depends on various factors, including the specific yeast strains used, the desired flavor profile, and the distillery’s production goals. 

A longer fermentation period may allow for more complex flavors to develop, while a shorter fermentation period can result in a cleaner, lighter spirit. 

Distilleries carefully monitor the progress of fermentation to determine the optimal duration for their desired bourbon style.

During fermentation, the yeast transforms the sugars in the mash into alcohol, laying the foundation for the subsequent steps of distillation and aging. 

The fermentation process is critical in shaping the flavor profile and character of the bourbon, as it produces a wide range of flavor compounds that contribute to the final product’s unique taste and aroma.

Distillation

Pot still distillation

What is pot still distillation?

Pot still distillation is a traditional method of distillation that involves the use of a pot still. A pot still is a copper or stainless steel vessel with a wide base and a tapered top, often resembling a large kettle. 

It operates on the principle of batch distillation, meaning that the distillation process occurs in discrete batches rather than continuously. 

During pot still distillation, the fermented mash is heated, and the alcohol vapors rise into the neck of the still, condense, and are collected as liquid distillate.

How does pot still distillation contribute to bourbon production?

Pot still distillation is integral to bourbon production for several reasons:

Concentration of flavors

Pot stills are known for their ability to capture and concentrate flavors. The pot’s still shape and copper’s presence contribute to removing impurities and developing complex flavor compounds.

This results in a spirit with a rich and robust flavor profile, capturing the nuances of the grains and other ingredients used in the mash.

Retention of congeners

Congeners are naturally occurring flavor and aroma compounds that contribute to the character and complexity of bourbon.

With its slower and more selective process, pot still distillation tends to retain a higher concentration of congeners than other distillation methods.

These congeners, including esters, aldehydes, and higher alcohols, contribute to bourbon’s unique taste and aroma.

Artisanal craftsmanship

Pot still distillation is often associated with artisanal production methods and small-batch bourbon. 

It allows distillers greater control over the distillation process, allowing them to tailor the spirit’s characteristics to their desired style and maintain a hands-on approach to crafting their bourbon.

Column still distillation

What is the column still distillation?

Column still distillation, also known as continuous distillation or patent still distillation, is a method of distillation that employs a tall, vertical column or rectifier. 

The column still consists of several stacked plates or trays that allow for multiple distillation stages to occur simultaneously. 

The distillation process is continuous, with the mash continuously fed into the top of the column and the final spirit continuously collected at the bottom.

How does column still distillation contribute to bourbon production?

Column still distillation has its own contributions to bourbon production:

Efficiency and productivity

Column stills are highly efficient and can continuously produce large quantities of spirit. This makes them well-suited for high-volume bourbon production, enabling distilleries to meet the demand for their product.

Refining and purification

Column stills are designed to separate different components of the mash based on boiling points. This allows for greater control over the separation of undesirable compounds, such as impurities and certain congeners, resulting in a cleaner and lighter spirit.

Consistency

Column stills offer a high degree of consistency and repeatability. The continuous distillation process allows for precise control over the distillation parameters, resulting in a consistent flavor profile and quality from batch to batch.

Smoothness and versatility

Column still distillation tends to produce smoother and more neutral spirits. This can provide a versatile base for blending and aging, allowing for the further development of flavors during maturation.

While pot still distillation is often associated with artisanal craftsmanship and small-batch bourbons, column still distillation has gained popularity among larger distilleries seeking efficiency and consistent production. 

Many bourbon producers employ a combination of both pot stills and column stills, utilizing the strengths of each method to achieve their desired flavor profiles and meet market demands.

Aging

Types of barrels used

What types of barrels are typically used for aging bourbon?

Bourbon is primarily aged in new, charred oak barrels. These barrels are typically made from American white oak, known for its favorable properties for aging whiskey. 

The barrels used for aging bourbon are often referred to as “bourbon barrels” or “charred barrels.” 

The barrel’s charred interior plays a significant role in imparting flavor and color to the aging bourbon.

How do different barrel types affect the flavor of bourbon?

While new charred oak barrels are the standard for aging bourbon, variations in the barrel type can impact the flavor of the bourbon. Some factors to consider include:

  • Oak species: Different species of oak, such as American white oak, European oak, or Mizunara oak, can impart distinct flavors to the bourbon. American white oak is most commonly used and contributes vanilla, caramel, and spice flavors.
  • Toast and char levels: The degree of toasting and charring of the barrels can influence the flavor profile of bourbon. Light toasting may introduce subtle flavors, while heavier toasting and charring can bring out deeper, smoky notes and enhance the extraction of compounds from the wood.
  • Barrel history: If a barrel has been previously used for aging other spirits, such as sherry, rum, or wine, it may carry residual flavors and characteristics that can subtly influence the bourbon during aging.

Aging process

How long is bourbon aged?

To be legally classified as bourbon in the United States, the spirit must be aged in new, charred oak barrels for a minimum of two years. However, the aging period for bourbon typically exceeds this minimum requirement. 

Many bourbons are aged for at least four years, while others can be aged significantly longer, ranging from six to twenty-plus years. The aging duration significantly impacts the flavor development and complexity of the bourbon.

Moreover, some distilleries go above and beyond by producing a unique expression known as “single barrel bourbon.” In this specialized method, each bottle is sourced from an individual barrel, allowing for variations in flavor and character that showcase the distinct qualities of that specific barrel.

What factors influence the aging process and flavor development?

Several factors influence the aging process and flavor development of bourbon:

  • Climate: The climate in which the barrels are aged plays a crucial role. In warmer climates like Kentucky, the bourbon interacts more actively with the wood, leading to accelerated maturation and more pronounced flavors. In contrast, cooler climates may result in slower aging and subtler flavor development.
  • Warehouse conditions: The environment within the aging warehouse affects the aging process. Variations in temperature, humidity, and airflow can influence how bourbon interacts with the barrel, leading to differences in flavor extraction and evaporation rates.
  • Barrel placement: The placement of barrels within the aging warehouse can also impact the bourbon’s aging. Barrels positioned higher in the warehouse tend to experience more temperature fluctuations and greater interaction with the wood, potentially developing richer flavors.
  • Master distiller’s expertise: The decisions made by the master distiller, such as barrel selection, blending, and when to bottle, can influence the flavor development and overall quality of the bourbon.
  • Time: Time is a critical factor in the aging process. As bourbon ages, it undergoes chemical reactions and undergoes oxidation, allowing flavors to develop and mellow over time. The length of aging determines the depth, complexity, and smoothness of the final bourbon product.

During the aging process, the bourbon interacts with the charred oak barrel, extracting compounds such as vanillin, tannins, lignins, and other flavor compounds. 

These compounds contribute to the distinct characteristics of bourbon, including its color, aroma, and taste. 

Aging allows the flavors to mature and harmonize, resulting in well-rounded and refined bourbon.

Bottling and Packaging

Filtering

What is the purpose of filtering bourbon?

Filtering bourbon serves several purposes, including clarification and refinement of the spirit. Filtering helps remove any sediment or impurities that may have developed during aging, resulting in a visually clear and visually appealing bourbon. 

It can also contribute to the smoothness and overall consistency of the final product by reducing any unwanted flavors or aromas that may have accumulated during aging.

How is bourbon filtered before bottling?

Bourbon can undergo various filtration methods before bottling. The two primary methods are:

Chill filtration

Chill filtration involves cooling the bourbon to near-freezing temperatures and passing it through a filtration medium, such as cellulose pads or diatomaceous earth.

This process helps remove any fatty acids, proteins, or esters that may cause cloudiness or haziness in the bourbon when exposed to lower temperatures.

Chill filtration is commonly employed to ensure visual clarity, particularly for bourbons intended for mass-market distribution.

Charcoal filtration

Charcoal filtration, also known as charcoal mellowing, involves passing the bourbon through a bed of charcoal, typically made from maple or birch.

The charcoal acts as an adsorbent, capturing impurities, off-flavors, and harsh compounds. This process can contribute to the smoothness and refinement of the bourbon, imparting subtle changes to its flavor profile.

Charcoal filtration is commonly associated with Tennessee whiskeys, such as Jack Daniel’s, but some bourbon producers may also employ this method.

Proofing

What does proofing refer to in bourbon production?

Proofing in bourbon production refers to adjusting the alcohol content of the bourbon to a desired level before bottling.

It is a measure of the alcohol content, expressed as a percentage of alcohol by volume (ABV). The term “proof” is traditionally used in the United States, where it represents twice the alcohol percentage by volume. [2]

How is the proof of bourbon adjusted before bottling?

The proof of bourbon is typically adjusted through the addition of water. Distilleries carefully calculate and blend specific quantities of high-proof bourbon with water to achieve the desired alcohol content. This process is known as proofing down. 

The precise proofing level is a crucial decision made by the master distiller, as it can impact the balance of flavors and the overall sensory experience of the bourbon. 

By adjusting the proof, distilleries aim to create a consistent and well-balanced product that aligns with their desired flavor profile.

Bottling and labeling

What are the steps involved in bottling bourbon?

The bottling process involves several key steps:

  • Preparation: Empty bottles, closures (such as corks or caps), and labels are gathered, inspected, and prepared for the bottling process. Quality control checks are performed to ensure that all materials meet the distillery’s standards.
  • Filling: The bourbon is carefully transferred from storage tanks or barrels into the bottles. Automated or manual filing systems ensure accurate volume and minimize spillage or product loss.
  • Closure application: Once the bottles are filled, closures such as corks, caps, or seals are applied to ensure a secure and airtight seal. This step helps maintain the quality and integrity of the bourbon during storage and transportation.
  • Quality control: Bottles are inspected for any defects, such as chips, cracks, or imperfections. Quality control checks may also include verifying the fill level, label alignment, and closure integrity.
  • Packaging: The filled and sealed bottles are packaged in boxes or cartons, often in predetermined quantities suitable for distribution. Packaging may also involve the addition of protective materials, such as dividers or padding, to ensure the safe transportation of the bottles.

How are bottles labeled and packaged for distribution?

Bottles are typically labeled and packaged with great attention to detail, as it is an essential aspect of branding and consumer appeal. The labeling and packaging process may include the following steps:

  • Label design and printing: Distilleries create distinctive labels that showcase their branding, product information, and legal requirements. Labels are printed with high-quality graphics, typography, and relevant information, such as the bourbon’s name, age, proof, and bourbon distillery details.
  • Label application: Labels are affixed to the bottles using automated or manual labeling machines. This process ensures accurate placement and alignment of the labels.
  • Packaging design and assembly: Distilleries often design custom packaging, including boxes, tubes, or other containers, to enhance the presentation and protection of the bourbon bottles. Packaging materials are assembled and prepared for the insertion of bottles.
  • Bottles and packaging combination: Bottles are carefully placed into their designated packaging, often with protective inserts or dividers to prevent movement or breakage during transportation. Packaging materials are sealed, and additional branding elements, such as stickers or sleeves, may be applied.
  • Quality control and inspection: Bottles and packaging undergo rigorous quality control checks to ensure they meet the distillery’s standards for appearance, functionality, and compliance with labeling regulations.
  • Storage and distribution: Once packaged, the bourbon bottles are stored in appropriate facilities until they are ready for distribution. They are then shipped to retailers, wholesalers, or directly to consumers, ready to be enjoyed.

The bottling and packaging process is an important final stage in bringing bourbon to market, ensuring that the spirit is presented appealingly and professionally while maintaining its quality and integrity.

FAQs

What makes a bourbon different from whiskey?

Bourbon and whiskey differ primarily in terms of the grain used and the production location. Bourbon, which is a type of American whiskey, must have a mash bill that includes a minimum of 51 percent corn and undergo aging in new, charred oak barrels.

How does whiskey turn into bourbon?

According to the American Bourbon Association, for a whiskey to be categorized as bourbon, it must be distilled from a mash consisting of at least 51% corn. Including corn in the mash is responsible for bourbon’s distinctively sweet flavor profile.

What is Kentucky bourbon?

Kentucky bourbon is bourbon whiskey produced in the state of Kentucky, known for its rich tradition and expertise in bourbon production. It is made from a mash bill containing at least 51% corn and aged in new, charred oak barrels.

Kentucky bourbon embodies the excellence associated with this iconic American spirit with its distinct flavors of caramel, vanilla, and oak.

References

  1. https://www.cnbc.com/2015/06/04/5-rules-that-make-it-bourbon.html
  2. https://www.aiche.org/resources/publications/cep/2021/august/chemistry-bourbon
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