After wading in barrels of the Scotch and Irish drams, it's time to turn our attention homeward, to that quintessential American spirit: good old bourbon whiskey. We'll look today at what makes bourbon unique, how it's made, and how it came to be.

What Is Bourbon?

In brief, bourbon is a whiskey, made predominantly from corn and aged in charred oak barrels. But if you've been reading this column for a while, you know that I'll probably hit you with a formal, legal definition of bourbon that complicates things. Indeed, here it is.

According to the United States government, bourbon sold in the United States must meet these requirements:

Made from a grain mixture that is at least 51% corn.

Aged in new charred-oak barrels.

Distilled to no more than 160 proof, or 80% alcohol by volume (ABV). In practice, most bourbon is distilled out at a lower proof than this.

Entered into the barrel for aging at a proof no higher than 125 (62.5% ABV).

Bottled at no less than 80 proof (40% ABV).

Bourbon is, as noted, 51% corn. The remaining 49% includes other grains. Usually, those grains include wheat, rye, malted rye, and malted barley, in any combination. Some distilleries, though, have experimented with rice, oats, and other grains.

Bourbon must be aged, but there are no specific requirements as to time. ("But wait! Doesn't bourbon have to be at least two years old?!" Read on.)

When we looked at the legal regulations about the manufacture of Scotch and Irish whiskies, we saw some language in them about the origins of the enzymes and yeasts used in fermentation. Bourbon has no such restrictions, so bourbon makers may use added enzymes to break down the grain mash.

We've already talked a lot about barrel aging in this space, but it's worth mentioning again. Bourbon requires the use of new, charred-oak barrels. This allows the barrel to impart more of its own flavors of oak, caramel, and vanilla into the whiskey than you get with Scotch, which generally uses second-hand barrels. We'll talk more about aging in a minute.

What Is Straight Bourbon?

Look at most bottles of bourbon on the market, and you'll see the term "Straight Bourbon" indicated prominently on the label. Straight bourbon must meet all the requirements of bourbon, but it has a couple of extra requirements that regular bourbon doesn't have:

Straight bourbon must be aged at least two years. If it is aged less than four years, the bottle must carry an age statement. The corollary to this is, if a bourbon carries no age statement, it's aged at least four years.

Straight bourbon may contain no added colorings, flavorings, or additional spirits.

If a straight bourbon carries an age statement, it carries the age of the youngest whiskey in the bottle.

The last bullet point implies that straight bourbon may be a mixture of bourbons (all of them straight), but there's a caveat: they all must be produced in the same state. "Straight bourbon" does not imply a single-barrel bourbon, or even a mix of bourbons all from the same distillery. In other words, a bourbon maker can purchase straight bourbons from other distilleries and mix them to create a new straight bourbon.

Bourbon Production

Bourbon starts with a "mash bill," a blend of grains that form the basis of the bourbon. Bourbon's mash bill, as noted above, must be at least 51% corn, although in practice, bourbons are made from 60–86% corn. The other grains used in bourbon are generally rye, wheat, and barley. Most distillers use only two of those three—either rye and barley, or wheat and barley.

As an aside, bourbon that uses wheat instead of rye is known as a wheated bourbon, and it tends to be softer and sweeter than a bourbon made with rye. Maker's Mark is the best known example (and y'all know a bit about Maker's already), but others include W.L. Weller and Old Fitzgerald. I doubt I'm the only one who started drinking bourbon by drinking wheaters, before moving on to more rye-forward bottlings. (A whiskey such as Bernheim Wheat Whiskey, incidentally, is a different beast; Bernheim is 51% wheat, with the remaining grains a mix of corn and barley. In other words, it ain't bourbon.)

Back to bourbon production. Ground-up grains are mixed with water, and then in most bourbons, a bit of mash from a previous distillation is added, to form a sour mash. (More on this in a bit.) New yeast is added, and the mixture is then fermented, before being moved off to a column still, also known as a continuous still or a Coffey still. Bourbon by law can't be distilled higher than 160 proof (80% ABV) but in practice, most bourbon is distilled out to between 130 and 160 proof (65–80% ABV).

Bourbon is generally double-distilled. The second pass may go through a pot still or another column still, depending on the whiskey maker.

The spirit that comes off the still is clear. Bourbon gains its color and much of its flavor from barrel aging. By law, bourbon ages in new charred-oak barrels. The charred wood provides caramelized sugars that add flavor to the whiskey.

When whiskey is aged in oak barrels, a number of variables influence the final character of the spirit. Climate plays a major role; as temperatures increase, whiskey expands, and the staves of the oak barrels absorb some of that volume; cold weather causes whiskey to contract back out of the staves. This movement of whiskey into and out of the staves gives whiskey tannins, an amber color, and a woody flavor. In warmer years, the whiskey will spend more time absorbed into the staves and pick up more tannins, color, and oak flavor; bourbon therefore ages faster in warmer years.

A barrel's location in its aging warehouse also influences how quickly the whiskey ages. Because hot air rises, temperatures on the top floor are generally higher than those below. To control for this variable, many distilleries rotate its barrels from higher floors to lower during aging.

What Is Sour Mash?

In addition to "Straight Bourbon," another term you'll see on some bourbon labels is "Sour Mash." (Jack Daniels, though not a bourbon, also uses sour mash, so this part of the discussion applies to ol' Jack as well.)

Simply put, the sour-mash process involves taking a small amount from a batch of previously used mash and adding it to a fresh batch. This makes the mash taste a bit sour, hence the name, but it doesn't make the resulting whiskey taste sour.

The advantages of this process are twofold, and they're all about the yeast. First, the sour-mash process creates a consistent environment for yeast from batch to batch, which means each new batch of whiskey is consistent with the last. This is one reason your favorite bourbon tastes the same from bottle to bottle. It also lowers the pH of the batch, which helps the yeasts in the batch ferment the mash more efficiently, boosting a higher yield of alcohol.

A few distilleries (Woodford Reserve, for example) have experimented with a similar process, called sweet mash. The difference here is that only fresh yeast is added to the mash; no "sour" yeasts are added from a previous batch. This may seem a minor difference, but the higher pH in the mash means that the mash ferments differently than in a sour mash, creating congeners you don't find in sour mash, meaning the resulting whiskey simply tastes different than a sour mash bourbon. Woodford's sweet mash, for example, is said to have more berry flavors than its sour-mash cousin.

All Bourbon Comes from Kentucky, Right?

It's a common myth that all bourbon is from Kentucky, but this isn't true. By U.S. law, all bourbon must be made in the United States. Otherwise, all bets are off. Now, 95% of bourbon on the market today happens to be from Kentucky, it's true. Other bourbon makers are located in Brooklyn, upstate New York, Massachusetts, Virginia, Ohio, Indiana, and Iowa, and I'm sure I've missed some.

Jack Daniels, by the way, is Tennessee whiskey. It is not a bourbon, but you knew that, right? More on Tennessee whiskey in a future piece.

But Why Is Kentucky Such a Great Place for Bourbon Making?

Kentucky is central to bourbon distillation for three main reasons. The first is corn, which is abundant in Kentucky and its surrounding states. The second is the limestone on which Kentucky is built; water that arises through limestone is iron free. Iron is bad for whiskey; it discolors the product (like a nail left in water) and introduces off flavors. Finally, the climate: Kentucky's hot summers and cold winters are ideal for efficient aging of bourbon.

A Brief History of Bourbon

I must be brief in detailing bourbon's long history; there's simply not space here to thoroughly detail the entire story of bourbon. Moreover, bourbon's earliest days are lost to the fogs of history, so it's impossible to present a truly comprehensive history.

Bourbon has its roots in the migration of settlers west from the original colonies, in the 18th and 19th centuries. The migrants included Scots-Irish descendants of the men who invented Scotch and Irish whiskies, but they also included other English, Welsh, German, and French settlers.

You may have heard that these migrants moved west in response to the taxation that later gave rise to the Whiskey Rebellion of 1789. This is partly true, but it's an oversimplification. Kentucky, at any rate, attracted Colonial explorers and settlers starting in 1750, nearly 40 years earlier than the Hooch Uprising. The reality was, the population of the colonies was growing so quickly, there was a vital need for western expansion. The whiskey-making settlement of Kentucky and Tennessee was inevitable, regardless of any political uprisings that may have happened.

Bourbon's antecedent in Colonial America was rye whiskey, made by gentleman farmers such as Thomas Jefferson and George Washington, but also distilled in great quantities by farmers throughout the central colonies. Rye suits the climate and soil of Virginia, Maryland, and Pennsylvania, and the grain thrives in those areas. Each region gave birth to specific styles of rye whiskey, but more on that in a later post.

The Godfather of Bourbon?

No one knows who "invented" bourbon, although as I'm about to explain, it could have been just about anyone, or even multiple people at approximately the same time.

Bourbon, at its most basic definition, is a whiskey made mostly of corn and aged in charred oak barrels. Kentucky's settlers already knew how to distill. The practice was used for both rum and rye in the colonies, and settlers brought the technology with them into Kentucky. The practice of aging spirits in charred oak was also well known in the 19th century, when bourbon first arose, so using charred barrels was a logical choice. Using corn was also logical; it was simply the most abundant grain in the area, and farmers found it more efficient and lucrative to haul whiskey to market rather than raw corn. So if you have knowledge of distillation and aging, and you have ample supplies of raw grain, bourbon whiskey almost invents itself. Who created bourbon? It really could have been anyone.

Various Kentucky families claim their patriarchs were the first to make whiskey in Kentucky. Claims date back to as early as 1776, but that may just be patriotism talking. We have historical evidence which establishes that the Reverend Elijah Craig was distilling whiskey by 1789, but it seems evident that he was working in a region where whiskey distillation was already common practice. The whiskey writer Charles Cowdery even argues that whiskey was made in the area that became Kentucky as early as 1774.

Was Elijah Craig the first person to put corn whiskey into a charred barrel? Legend (and clever marketing) would tell you this is so, but there's simply not enough historical proof to support the claim.

Bourbon and Farming

Prior to becoming a commercial and industrial product, bourbon was originally an agricultural one. The first bourbons were made by farmer-distillers, using pot stills of anywhere from 20 gallons to 200 gallons in size. These farmers made whiskey in fall and winter after their crops were in, after the corn was dry enough to grind and make whiskey from.

Farmers made bourbon for their own consumption and also to sell; grain was hard to transport and even harder to market, so it was only practical to sell whiskey instead. They would sell it to grocers who in turn would then sell it, by the barrel, to bars and saloons. Whiskey was also loaded onto flatboats, at a port on the Ohio River now called Maysville, Kentucky, and shipped down the Ohio and Mississippi rivers to New Orleans.

Bourbon sales were highly profitable for farmers throughout the 19th century. The raw ingredients (corn, other grains, and water) were extremely inexpensive, of course, but the final product sold for a premium.

Prior to Prohibition, there were 2,000 distilleries just in Kentucky alone. Today? About ten.

Why the Name "Bourbon"?

The simplest explanation for the name "bourbon" is that it's named for the Kentucky county in which it was invented, Bourbon County. That explanation also happens to be wrong, because "bourbon" in Kentucky predates the establishment of Bourbon County.

Early settlers used French place names in Kentucky as a means of gratitude toward the French for their support during the American Revolution, so this explains why bourbon is named indirectly for a French royal house.

In its early days, the land we now call Kentucky was part of Virginia, and it was divided, subdivided, and divvied up again several times into smaller and smaller counties. Today's Bourbon County, Kentucky, is small, but when Bourbon County, Virginia, was established in 1785, it was a huge region, encompassing dozens of today's counties. As we've seen, whiskey production was already in full swing by then, with dozens of farmer-distillers pumping it out by the gallons.

I mentioned earlier that whiskey was loaded onto flatboats at the port at a town now called Maysville, Kentucky. The port already existed when Bourbon County was established around it. Whiskey was transported to the port from throughout the entire region, before being loaded onto flatboats.

The entire region of the vast, original Bourbon County came to be called "Old Bourbon," and any whiskey shipped from the port came to be known as "Old Bourbon Whiskey," no matter what its place of origin.

Bourbon's Fall and Rise

Bourbon wasn't initially sold the way we think of it today. You wouldn't go to a liquor store and get a bottle. Bottling didn't become standard until 1890s. The main package was the barrel, and if you wanted bourbon at home, you'd go to your local saloon and ask the barkeeper to fill a flask or bottle for you from a barrel he kept behind the bar. It's similar to growlers at some of today's brewpubs.

The 20th century dealt two blows to the bourbon industry. First, obviously, was Prohibition. Most small distilleries closed down permanently. Those that survived did so only via a loophole in the law that allowed doctors to prescribe whiskey for medicinal purposes. Over six million whiskey prescriptions were written during the years of Prohibition, which meant a lot of people were "sick."

The second hit on bourbon came during the second World War, when the Federal government called on them to stop producing liquor and instead produce fuel alcohol and penicillin (a byproduct of fermentation).

In general, the story of the first eight decades of the 20th century is one of decline for bourbon whiskey. By the 1970s, most younger adults thought of brown spirits as something their parents and grandparents drank. Young people wanted lighter and trendier spirits, such as vodka and tequila. They also developed a taste, of course, for non-alcoholic drugs.

What brought bourbon back? Wine and Scotch, ironically. Wine's star shone brightly in the 1970s, as marketers found ways to encourage customers to host wine tastings, serve wine dinners, and buy books and magazines about wine. Scotch marketers took a hint from wine's success and started holding scotch tastings and whisky dinners.

Bourbon Today

Bourbon has rebounded impressively from its 1970s nadir. In 2010, the American whiskey industry (which includes bourbon and Tennessee whiskey) sold 15.4 million cases of whiskey, accounting for $1.9 billion in revenue—during the worst economic conditions since the Great Depression. Export sales are higher than ever, up 286% just in France. Bourbon marketers are finding an enormous potential in China and India, and they're exploring new markets elsewhere in Asia and in Africa.

The money flooding the market has led to plant expansions at Wild Turkey, Jim Beam, and Maker's Mark, just to name three. Four Roses, Buffalo Trace, and Woodford Reserve have expanded and updated their visitor centers. Tourism in Kentucky is booming, with nearly 2 million people visiting the Kentucky Bourbon Trail in the last five years.

For geeks like me who love American whiskey, this is an exciting time; the industry is full of innovation. I mentioned in an earlier post the work that Buffalo Trace is doing, experimenting with the variables that make a great bourbon. Brands such as Bulleit and Knob Creek are expanding into rye production. Maker's Mark introduced its Maker's 46 offshoot a couple of years ago, experimenting with a new aging technique that adds unique flavors to the bourbon.

Every major brand has single-barrel, small-batch, and cask-strength variations on the market, often at superpremium prices. On the other hand, today's bourbon makers are so efficient that they can sell a great product at relatively low prices, as anyone who buys Evan Williams by the handle will attest.

The Elephant in the Room: GMO Corn

I can't leave this topic, though, without sounding what may be a bit of a sour note. Earlier this year, the web magazine Grist published an article about the use of genetically modified corn in bourbon production.

Essentially, nearly every distillery uses GMO corn to make bourbon. The distilleries are in a bind here: on the one hand, European consumers demand the use of non-GMO ingredients; on the other, non-GMO farming in this country is dwindling fast, vastly reducing the amount of non-GMO corn available on the market.

If you're concerned about the use of GMO products in your whiskey, the Grist article offers two organic, non-GMO choices, and to my palate at least, both are excellent-tasting options: Four Roses and Wild Turkey. But even the master distillers at those brands express pessimism that they'll be able to hew to the non-GMO standard in the future.

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