Bourbon’s unique flavour is derived from the various processes used to make it. By understanding how bourbon is made, you can obtain a greater appreciation for its flavour. In this guide, you will learn exactly how bourbon whiskey is made as we cover the following points:

Use the links above to jump ahead or scroll down to read it all.

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How To Make Bourbon Whiskey

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What Is Bourbon Whiskey Made Of?

Whiskey Grains - Wheat, Barley, Rye, Corn

Left To Right: Wheat, Barley, Rye, Corn

All whiskey is produced by fermenting grain and then distilling it. Incidentally, most clear spirits like vodka and gin are also made by following a similar process. However, they remain clear because they aren’t aged in oak casks.

The fermented grain is referred to as a “mash” and it’s not unlike beer. However, the ingredients are a little different when making whiskey. The composition of a mash may consist of the following ingredients:

  • Barley
  • Corn
  • Rye
  • Wheat

The rye and barley can be malted beforehand, which involves humidifying the grain so it opens and begins to germinate. The mash’s chosen ingredients and their proportions are referred to as a “bill”.

In order to be recognised as bourbon whiskey, the mash bill must consist of at least 51% corn. The bill’s remaining 49% can be any combination of the above ingredients, including more corn if desired.

The ingredients are placed in a large steel container called a mash tun and mixed with water. Yeast is added so that the mash can ferment. Modern tuns are usually equipped with pumps and propellers so that the mash continues to mix.

Occasionally, remaining mash from a previous distillation may be used as well. This process is known as a sour mash and it can help ensure consistency between each batch. Its name is derived from the acidic flavour brought on by special lactic bacteria that helps preserve the mash and prevent it from soiling.

How Is Bourbon Whiskey Distilled?

Once the mash bill has properly fermented, it is ready to be distilled. There are no regulations as to what type of still can be used and some producers might even combine different ones.

Artisanal distilleries may opt for the traditional alembic pot still. This type of still may have improved since it was introduced in Europe by the Arabs during the 8th Century Umayyad conquest, but it fundamentally remains the same.

Copper pot stills require a lot of skill to use effectively and the process must take place in batches, which is time-consuming and labour-intensive. However, a master distiller will have more control over the final product and its flavour.

Pot stills produce toxic distillates called the heads and tails. These are often discarded but a portion may be kept for future batches. To make the process both easier and quicker, the pot stills might feature additional stills called “retorts”.

These allow the heads and tails to be easily recovered, which are distilled again to remove more impurities. The idea was developed in the early 19th century by Édouard Adam but his invention never really took hold in France and Europe since Aeneas Coffey’s continuous column still was invented around the same time.

However, Adam’s retort system was exported to the Americas via the French colonies sooner, which meant that it was more widespread on the other side of the Atlantic. At the time, the Coffey still required advanced steam technology to work, which wasn’t available to most artisanal distillers.

Today, though, the larger commercial distilleries tend to favour the continuous column still. Thanks to its design, it results in a far greater amount of distillate at a higher proof with less waste and less work. However, it arguably retains less flavour from the original mash.

How Is Bourbon Whiskey Aged?

Whatever technique used, the process results in a clear distillate, which is referred to as a “white dog”. Depending on the type of still used, its strength may range between 65% and 80% ABV, but it must not exceed the latter concentration.

Bourbon whiskey may not be aged in used casks and coopers are commissioned to make new ones with each batch. Larger whiskey brands may have an in-house cooperage but most producers will rely on independent artisans.

Typically, barrels are produced from American white oak and the methods remain relatively artisanal. Furthermore, their interior is charred with a naked flame beforehand, which we explore in further detail below.

Since used bourbon barrels have little use in the USA, they’re typically exported to distilleries around the world. Scotland is one of the most famous countries to use ex-bourbon barrels for its own whisky. Otherwise, they’re also used in the Caribbean for rum as well as Ireland, Canada, and Mexico.

Before it’s placed in the oak casks, the white dog is hydrated to no more than 62.5% ABV but it may be less if desired. This regulation is put in place to prevent producers from using fewer barrels by ageing a highly concentrated distillate.

Why Are Oak Bourbon Barrels Charred?

In our guide to the history of bourbon whiskey, we explore one of the leading theories of why the technique was first introduced. Here, though, we’ll explore why it has endured and the effects it has on the whiskey.

As mentioned above, charring is undertaken directly by the cooper after the barrel has been manufactured. Producers will often order custom levels of charring depending on the intensity of flavour that they wish to create.

Charring sounds like a long process but it takes only a few seconds. The lightest charring lasts just 15 seconds and the heaviest is less than a minute. Rather than impart a smoky flavour, as many people believe, charring primes the wood before it comes into contact with new whiskey.

The oak’s grain is opened by exposing it to an open flame, which allows increases its contact with the whiskey. Meanwhile, the heat provokes a reaction that releases flavourful chemicals such as lactones and hemicellulose.

For instance, the wood’s cellulose crystalises into sugars while lignin is extracted from the sap. After prolonged contact, these two compounds are absorbed by the distillate and will eventually result in caramel and vanilla flavours respectfully.

How Long Is Bourbon Aged?

There is no minimum ageing period for standard bourbon whiskey and it can be bottled after just a few months. However, it is expected that premium bourbon whiskey is aged for a bit longer, to say the least!

Although you might be used to Scotch whisky that is often proudly branded with double-figure age statements, remember that Scotland is quite cold. As a result, it requires a longer ageing process to achieve the same results as whiskey matured in most parts of the USA.

Bourbon that’s a decade or older isn’t unheard of, mind, but they’re generally rarer these days. When the taxed bonding period for ageing whiskey in warehouses was lengthened in the 1950s, brands began experimenting with age statements.

By the 1990s, these became very fashionable and many producers started releasing whiskeys that were over 10 years old. Yet, stocks depleted in the warehouses with the bourbon boom that soon followed. Since then, bourbon whiskey brands have either reduced their age statements or even removed them altogether.

Kentucky bourbon can be aged for as little as one year in order to bear the state’s name on its label. To qualify as a straight bourbon, the whiskey must be aged for at least two years.

Meanwhile, straight bourbon aged for more than four years doesn’t require an age statement. If it fulfils additional requirements, the four-year-old straight bourbon may also be labelled as “bottled-in-bond” whiskey.

Is Bourbon Blended?

It’s commonly believed that only “blended” bourbon is blended. After all, it’s in the name. Indeed, blended bourbon is a variety of bourbon whiskey that is produced by mixing in different bourbon batches with high-proof spirit. It must, however, contain at least 51% straight bourbon whiskey.

Apart from single-barrel expressions, which by definition are bottled directly from just one cask, all bourbon can be blended as long as it respects certain requirements.

For instance, straight bourbon can still be recognised as such as long as it’s blended with other straight bourbon produced in the same state. Needless to say, the second rule certainly applies to Kentucky bourbon, too.

Bourbon of different ages, batches, and caskings may be blended together in order to create unique flavours. In order to avoid confusion, producers will often refer to the process as “mingling”.

Finally, if the bourbon whiskey is to bear an age statement, the year on the label must equal the age of the youngest batch used in the blend.

Does Bourbon Age In The Bottle?

Types of Bourbon Whiskey

Bourbon is bottled at a minimum of 40% ABV, a requirement in both the USA and EU, once the producer deems it ready to drink. However, some distillers may bottle their whiskey at a high-proof strength, which can even be above 70% ABV! Similarly, bottled-in-bond bourbon must have a final ABV of at least 50%.

Bourbon stops ageing as soon as it’s removed from its oak cask and poured into a bottle. Glass is an inert substance and the whiskey doesn’t undergo any further chemical reactions when contained inside it.

For this reason, glass demijohns or “Dame-Jeannes” are used for storing particularly old alcoholic spirits like cognac. Additionally, these are usually sealed by only a cloth cover, which allows for subtle air exchange.

Indeed, bourbon whiskey won’t age or even change as long as it remains sealed in its bottle. Once opened, however, it may begin to oxidise. This process doesn’t develop any additional flavours, but some spirits do occasionally improve once exposed to a bit of air.

Eventually, though, the whiskey will begin to degrade due to this air exposure. Nevertheless, it may take years or even decades for it to lose a noticeable amount of flavour.

What Next?

Now that you have learned how bourbon is made, take a look at some more of our resources!

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