Distilled spirits have been around for millennia, and the class of spirits known as whiskeys got their start many centuries ago in Britain. Immigrants from the north of the British Isles began to produce distilled liquor from local grains readily found in the new colonies (which later became the United States of America) by. Eventually, a specific type of whiskey became institutionalized by the US Congress into what we call Bourbon today. The official designation of Bourbon was formalized in 1964, with further specifications provided under certain acts of Congress in 2009.

History of Whisky

We find references in ancient civilizations such as Babylon, Egypt, India, China, Greece and Rome about the process of fermentation and distillation. Alcoholic spirits were introduced in Britain by the Romans in the 13th or 14th century. The name whisky came from the Scots Gaelic term “Uisge beatha”, from the Latin name “aqua vitae” (“water of life”, referring to distilled spirits). It was later translated to “uske” before it reached the modern name.

Whisky manufactured in the British Isles thus has a rich history, dating back almost 700 years. The art of choosing the right grains, fermentation, distillation, aging and creating the finished product that we know as Scotch Whisky or Irish Whiskey today went through a significant evolution over these centuries – whether it be in techniques, refinements or marketing. As an example, Single Malt Scotch being at the head of the pecking order of world whiskies is a phenomenon that only came into being during the World War I period – when a combination of Prohibition and other market forces caused a significant decrease in demand for Irish Whiskey.

Whiskey (with an “e”, from the Irish spelling) production in the United States got off to a start in the 18th century, primarily from the migration of Scot-Irish and Irish immigrants from the north of Britain. There was an active concentration of such people, along with other immigrants from England, Germany and other European natures in Appalachia. The new colonists used whatever grains they could find easily in the area, which in turn gave rise to a host of local crafts and techniques to produce what was designated as “moonshine”. Over time, moonshine fermented and distilled in Kentucky (principally) came to be known as Bourbon – for a number of reasons (maybe legitimate or simply local legends) as outlined below.

History of Bourbon

Post the Great Depression era (1929-33), the US underwent a number of major changes. In terms of whiskey, an important milestone was the end of Prohibition in 1933. The popularity of Bourbon Whiskey as a “Made in America” brand began to skyrocket during this period. Finally, in 1964, the US Congress declared bourbon to be a “distinctive product of the United States” and asked for the ban on imports of foreign liquors under the label of Bourbon.

There are multiple theories about the origin of “Bourbon”, which got popularized more than a century earlier. The name likely came from the Bourbon dynasty in France, though the precise reason that the name came to be attached to local whiskey is the stuff of legends, not always with enough facts to support theories. It’s certainly true that the French dynasty lent its name to Old Bourbon county in Kentucky, which was one of the earliest destinations for settlers in Appalachia. This area became a major hub for the production of local liquor being made from corn mash for the most part. The locally manufactured liquor was loaded on boats that plied the Mississippi River down to New Orleans, which also had the famous Bourbon Street (image below). During the Revolutionary era and later, the high price of French cognac made the liquor from Kentucky popular, boosting the amount of trade from Kentucky to New Orleans and overseas.

Bourbon Street

While Elijah Craig and Jacob Spears have been mentioned as people who helped popularize the name Bourbon, those stories are likely apocryphal. The names of the county where the liquor was manufactured or the famous street at its destination may or may not be the origin either. There have been more prosaic explanations, such as the believable theory that when barrels of whiskey were loaded on to boats – to be delivered to New Orleans – they were stamped “Bourbon” to distinguish the products using the name of their origin.

Whatever be the etymology, Kentucky has remained the epicenter of Bourbon production. The ground under is rife with limestone caves, which filter water to a purity which is considered vital for the production of the whiskey in the area (as in the neighboring state of Tennessee – which produces Tennessee Whiskey, a close cousin of Bourbon).

The Legal Definition of Bourbon

Is Bourbon simply a synonym for whiskey manufactured in Kentucky? You could make a case for it – after all, according to the Kentucky Distillers’ Association, 95% of the world’s supply of Bourbon does come from the Bluegrass State. However, Bourbon can be produced anywhere in the US (note the emphasis) – as long as it meets the Federal Standards of Identity for bourbon (namely 27 CFR 5.22).

Following the proclamation by the US Congress in 1964, bourbons were considered to be whiskies manufactured in the US exclusively. These standards were further strengthened by proclamations in 2009. There are two aspects to the definition of “bourbon”, it must be produced in the US according to generally acceptable standards, and further, it must meet the definitions below.

By the mandate of the Federal Standards of Identity, Bourbon whisky must:

  •  Be produced from a fermented mash of not less than 51% corn
  •  Processed at the distillery into a mash
  •  Fermented, only by adding yeast
  •  Produced at a level not exceeding 160 proof (80% alcohol by volume (ABV))
  •  Stored in charred oak barrels at temperatures not higher than 1250F
  •  Bottled at no less than 80 Proof (40% ABV)

In reality, while the corn level is required to be at least 51%, most common bourbons have corn comprise more than 60% of their mash, as noted below.

Upon production, bourbon does not have the same requirements as Scotch for a minimum period of time that the distilled liquor must further be aged in charred oak casks – there are bourbons that are put out for sale after being aged for three to six months.

There are exceptions, however, which must be clearly noted in the labelling, and whose guidelines follow the Bottled and Bond Act of 1897. For example:

  •  Straight Bourbon Whisky will have been aged for two years or more;
  •  European countries often require Bourbon marketed there to have been aged for three years or more; and
  •  Bonded Bourbon is unblended bourbon whiskey which has been stored in oak casks for at least four years and which is   bottled at 100 proof (50% ABV)

There are some other requirements, such as the final product not containing added substances other than water and caramel coloring.

The production of Bourbon goes beyond these guidelines. The mix of grains, type of yeast used, distillation process, specifics of ageing in new oak barrels and storage… all play a significant role in the finished product. That’s how you get the range of tastes that good Bourbons produce.

The Raw Ingredients of Bourbon

The raw ingredients are simple – Bourbon uses all-natural ingredients. The main ones used are corn, other grains such as rye, barley or wheat, fresh spring water (preferably) and yeast.

The Use of Corn and Other Grains

As mentioned above, Kentucky Bourbon has a requirement of having at least 51% corn in its mash. Each distillery has its own unique mash bill, with the ingredients carefully chosen to produce a specific taste. In reality, most bourbons are produced with 60-80% corn.

Other ingredients used are rye and malt barley, often 10-15% each. Some specific distillers will add 10% or more wheat to their mash bill, which makes the taste milder and smoother. A few well-known brands’ mash bills are presented below:

Woodford Reserve – 72% Corn; 18% Rye; 10% Malted Barley

Jim Beam – 77% Corn; 13% Rye; 10% Malted Barley

George Dickel – 84% Corn; 8% Rye; 8% Malted Barley

Makers Mark – 70% Corn; no Rye; 14% Malted Barley; 16% Wheat

Koval – not known, secret recipe single grain whisky

As can be seen above, there is strong concentration of corn, but the mashes vary across distilleries. In some cases, different mash bills are used for different brands by the same distilleries. Also, precise recipes and modifications are often kept secret.

The different grains are ground separately – usually crushed to open the husk and made into fine flour – then stored separately.

bourbon bottles


Fresh spring water is preferred when producing bourbon, so the starch can be cooked, and the sugar extracted from it. The water should not impart any additional flavors to the final product. The fresh spring water available in the bourbon producing areas in Kentucky is considered to be extremely pure, filtered by the limestone rock formations in the area. The availability of such pure water may be one of the reasons that bourbon production is concentrated in this area.


Surprisingly, or maybe not so surprisingly, the choice of yeast is important to bourbon distilleries. Different strains of yeast produce different levels, types and rates of reactions on the grains – and as such, premier distilleries carefully protect the variety of yeast they use. During Prohibition, many yeast strains were preserved in cold rooms for over a decade so that they could be resuscitated later – yeast is a big deal no matter how one looks at it.

Different bourbons use different, proprietary strains of yeast, which are usually cultivated in large dona tubs prior to being used.

Grain Cooking, Mashing and Fermentation

The first step in the bourbon-making process is the choice of grains as mentioned above. The next step acquires greater importance in bourbon production – unlike in the production of Scotch. The latter uses barley, which can turn starch into sugar (the desired outcome) during germination, with the help of certain enzymes. With corn, rye and un malted barley a different method is needed. The finely ground grains are cooked at varying pressures and temperatures for roughly half an hour to create the mash bill. Corn requires high temperatures (above 1140C), substantial pressure and longer cook times compared to rye and barley.

The grain mash is cooled down, once ready. Yeast is then added to the fermenter, in a proportion larger than the amount of mash. After an average of three days of fermentation, beer with approximately 9% ABV (ranges between 8-9.5% ABV) is produced. During this stage, the organic materials and carbohydrates decompose, producing ethanol (C2H5OH) along with by-products such as methanol (CH3OH), a number of congeners and carbon dioxide. Parts of the stillage (described later) is also added into the mix at this stage. The size of the fermenters can vary from “large” to “giant” – the fermented product is emptied into beer wells. Since bourbon is produced in column stills (see below), it is important to keep a large supply of beer at hand so the still never runs dry.

The beer is then distilled into white dog, which is the name used for raw whiskey. Tasting the white dog as batches are being produced is a time-honored tradition for bourbon distilleries.


As mentioned above, distillation is a very old process – described in cuneiform tablets from Ancient Mesopotamia 4000 years back. Modern distillation has gone through a number of evolutions but has proved to be a remarkably durable and stable process in terms of the methods used, type of stills and materials chosen to make stills.

Types of Stills Used

Unlike Scotch whisky, where distillers traditionally use copper pot stills, bourbon is manufactured using Column Stills, which were invented by Robert Stein in Scotland in 1826. These are large and tall variations (5 to 20 m high, 70-150 cm in diameter) of Agnus Coffey’s Continuous Still. Floors with holes are inserted into the pipe. The edges of the holes are bent upward, so liquid cannot flow down through them. Pipes are inserted to allow liquids on each floor to flow down to the level below. Vapors created during the process can flow upwards through the holes.

Column Stills often use steel, aluminum or other metals. Copper has to be cleaned periodically, making its use in column stills impractical. It is common, though, to use copper “doubler” pots at the end of the bourbon manufacturing process to help remove some highly volatile, noxious sulfurous compounds – such as dimethyl trisulphide (DMTS) and the toxic ethyl carbonate – formed during the distillation process.

The Process of Distillation

As described above, the fermented beer contains ethanol, which is “polluted” with a number of carbon dioxide and congeners – some of which range from noxious to toxic. Distillation is a process whereby these “bad” compounds are being taken out while retaining the good ones.

To begin the distillation, the white dog is fed into the middle of a Column Still and heat is turned on at the bottom. This creates two separate flows within the column pipe. Liquid beer keeps running down to lower floors through the tubes that have been inserted for that purpose, while evaporated alcohol rises up through the holes towards the top of the column. Due to the height, it is possible to regulate the temperature in a way that alcohol stays in its gaseous state at a temperature between 780-850C, while the beer at the bottom cooks at 950-1000C. The temperature at the top is important – Ethanol boils at around 78.40C.

At the top of the column, the mixture being produced can be distilled to a strength between 120 and 160 Proof (60-80% ABV) – the taller the column, the higher the ABV. The alcohol is extracted from the still and fed through a “doubler”, a copper pot which helps improve the taste of the whiskey through a catalytic conversion process. As described above, this step removes some unpleasant odors and adds back some fruity aroma.

There is an art form to avoid getting too much of the “Foreshot” or “Head” liquid produced at the lower ranges of temperatures, and the “Feint” or “Tail” liquid produced at the upper range of temperatures. Choosing the right “cut” is a skill honed with practice by master distillers. The central “cut”, which contains mainly ethanol and water, but also retains aroma and taste producing compounds that had been produced during fermentation, is the desired output.

Stillage and Sour Mash

As the continuous distillation continues, the liquid collecting at the bottom contains water, remnants of grain and fibers. This mix, called “stillage”, is often used for animal feed. Part of this stillage can be fed back into the fermentation process – this is what produces “sour mash”. While brands that tout sour mash whiskies market the taste that is produced, the real use of the sour mash is to enhance the acidity of the beer mixture, which produces ideal conditions for the yeast to work properly.


Unlike Scotch, Bourbon can be marketed after three months in a new wood barrel, though there are exceptions for “Straight” or “Bonded” bourbon, as explained above.

Choice of Barrels

By law, Bourbon must be aged in new oak barrels. Bourbon barrels are made from new American white oak, each typically holding 53 US Gallons (about 200 liters). These barrels can only be used once for storing and ageing bourbon – the casks are then resold for various other uses, notably for ageing Scotch whisky.

Before use, the barrels are staved and then toasted over a small fire, to the point where the wood sugar in the staves inside caramelize to a certain extent, creating a reddish layer. Toasting often lasts for 11-14 minutes. After this, a stronger fire is used (for around 9-12 seconds) to char the inside of the barrel. The sugars released from the oak surface adds vanillin to the mix of the flavors being generated within the cask as the whiskey comes in contact with it.

What Happens during Ageing

Typically, good bourbon is aged in the cask for 2-3 years, during which time the young oak wood (post toasting and charring) imparts significant flavor to the new distillate of whisky or wine. The average bourbon can be up to 62.5% ABV, which means that a significant amount of flavor is imparted to the stock.


The warehouses used by various bourbon manufacturers typically have multiple-floors. One of the issues that need to be addressed is how to create a comfortable temperature during storage – given that the top of the warehouse is hot and the bottom floors very cool, almost airconditioned. Different distillers will use different techniques to ensure that the quality of the whiskey being bottled is uniform. Makers Mark will physically rotate the barrels to give them time to mature in a cool environment. Others may avoid this labor-intensive step, instead using barrels from different locations within the warehouse when mixing the final product for bottling.

The additional benefit of not rotating barrels is that there is an area in the middle of the warehouse where the distiller can segregate and store special batches – for example, stock meant to be bottled and marketed as small batch or single barrel bourbon.

Bottling and Selling Bourbon

Given the high volumes of production, almost all major bourbon distillers run their own bottling lines. Bottles can be made out of glass or plastic, with sizes suited to specific markets – for example, 0.75 liters for the US and Japanese Markets; 0.7 liters for the European market; 1 liter for duty-free sales. Special sizes are also available, such as the Flat (0.2 liter) and Half-Gallon (1.89 liters) bottles.

Different types of bourbons add flavors to well-known cocktails such as Manhattans, Whiskey Sours, Old Fashioned and Mint Juleps. Connoisseurs will recognize the unique characters of the base bourbon, which makes them popular for use in homes and drinking establishments.

Makers Mark Bourbon

In Conclusion …

While the processes described above may seem “run of the mill”, the production of good Bourbon is anything but. Master distillers look for unique flavors that can be created on a repeatable basis – and marketed with the same taste, mouthfeel and consistency as possible.

Good Bourbon is neither cheap trash nor indistinguishable – however, there are specific markers that one must look for.

Treating a Bourbon as a pounding whiskey to be used in cocktails is one thing, but there are ways to savor the offering and its subtle textures. Try to do so the next time you sip one, perhaps it will change your views on the authenticity and uniqueness of the vintage you are savoring.