Distillers talk about craft, but when it gets down to it, they will tell you the alchemy that creates bourbon comes down to six things: wood, yeast and grain, fire, rain and time.
It all begins with the water, naturally filtered through Kentucky's limestone karst landscape to remove nasty-tasting iron.
Distilleries were built near rivers and other water sources to ensure a good supply because it takes a lot of water just to make a small amount of bourbon.
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Four Roses Distillery in Lawrenceburg gets its water from the Salt River. According to master distiller Jim Rutledge, they pull 1.3 million gallons of water a day, with 1 million gallons of it for cooling the cooked mash.
"Water from the river has the minerals in it that gives it a lot of the flavor," Rutledge said.
Many distilleries rely on city water these days and go to great lengths to remove what municipal treatment plants put in.
In part because Four Roses still relies on river water, the distillery still shuts down every summer for a while.
"Old-time distillers thought they couldn't run the operation in the summer because the water was bad," Rutledge said. Really, the problem was the water got too hot, he said. "To me, the best flavors are generated in grains fermented in cooler temperatures. It is inefficient to chill the water before it chills the mash, so we shut down in the summer. The only ones that can run year-round have an underground aquifer."
Heaven Hill, which operates its Evan Williams distillery in downtown Louisville, uses city water. It will only shut down for a week or two in the summer just to give the plant time for upgrades and maintenance. Then the distillery plans to be back to running three shifts, six days a week.
Distilleries are very particular about their corn, which often comes from Kentucky or Indiana farmers. Kernels must be perfect, smell good (they microwave it to see how it smells), and have the right moisture content.
"For 53 years, our corn has been sourced from a small geographic area in Indiana — one grain elevator," Rutledge said. Four Roses uses about 60,000 bushels of yellow No. 2 corn — "yellow dent" — a year.
Bigger distilleries are just as picky but want even more corn.
Heaven Hill, which has the second-biggest-selling brand of bourbon in Evan Williams, went through 2 million bushels of corn last year. It will go through even more after the Louisville plant adds new fermenter tanks this year, said master distiller Craig Beam.
Jim Beam, which also owns Maker's Mark in Loretto, goes through well over 120 acres of corn a day to keep its distilleries going, said Fred Booker Noe III, Beam's master distiller.
Some buy the grains and then grind or roll it themselves. Town Branch in Lexington buys its corn cooked and pre-gelatinized to save time and space, said Mark Coffman, master distiller of parent company Alltech.
Bourbon must be at least 51 percent corn, but the recipe for the rest varies, and not everybody will say exactly what they use. Some add wheat, but most use at least some rye, which imparts a spicy flavor.
The real key is barley that is malted (or germinated). The barley malt, which is the same used in beer and malted milkshakes, has enzymes that convert the starches of the cooked grain to sugars to feed yeast.
Most make just one or two recipes; it's what happens to it afterward that changes the flavor.
Wild Turkey in Lawrenceburg uses one recipe for bourbon and one for rye whiskey, said master distiller Jimmy Russell. That's it.
But it makes a lot of it: Russell said his distillery each day fills 12 fermentation vats, each holding 30,000 gallons.
The vats are where the real work is done — by the yeast.
Everybody's yeast is special.
It really is, and it has to be. Bourbon owes a lot of its flavor to what is essentially yeast poop. (The same could be said of any fermented liquid.)
When you smell or taste a flavor and say, "This smells like banana." It isn't like banana, it is banana, or rather the exact chemical compound that gives bananas their flavor. The microscopic yeast has generated that compound as a byproduct of consuming the sugars.
The established bourbon brands are made with yeast that has been specially cultivated for decades. The original strain is kept frozen and periodically analyzed to make sure it has not mutated.
Four Roses uses only two grain recipes but has five different yeast strains that can combine to make 10 different recipes and a nearly infinite number of flavor variations.
Maker's Mark is proud of its yeast, too.
"We've got the Samuels family yeast they brought over from Scotland," Greg Davis, Maker's Mark master distiller, said, referring to the family of its founder, Bill Samuels Sr. "And we DNA fingerprint it every year and grow it from the mother strain. You change the yeast, you change the flavor."
Wild Turkey's yeast "was here when I got here" almost 60 years ago, Russell said.
Woodford Reserve's yeast was cultivated from the Brown family's original Old Forester strain, said master distiller Chris Morris.
The yeast works for three to six days to consume the sugar and convert much of it to alcohol. By the time it is done, it will be about 8 percent alcohol before it goes through the still.
Although some distillers use a pot still in the process, the larger ones rely on multistory column stills, which use steam to vaporize the alcohol out of the fermented mash.
Maker's Mark, Woodford Reserve near Versailles and Town Branch have beautiful copper stills, but a lot of bourbon making looks much more industrial. (Even regular Woodford Reserve is "batched," or married, with bourbon made by parent company Brown-Forman in Louisville in its column still.)
Heaven Hill is typical: The Evan Williams maker has two 75-foot column stills with 29 "stripper" plates to pull the alcohol out of the mash. That's 150 feet of steam distillation running nearly around the clock.
Although distillers all use the same basic science to create their products, by the time they get to the alcohol called "white dog" — what comes off the still before it goes into a barrel — each tastes surprisingly different because of the different recipes and the different yeast strains.
The real magic of bourbon making happens in the barrel.
Bourbon is bourbon as soon as it touches wood. But it can't be called "straight" bourbon for two years, and it isn't good bourbon until it has been in there a while longer.
The barrel must be new oak and must be charred on the inside, but that allows for a surprising amount of variation. Each distiller has its own particulars: how the wood is aged, where it comes from, how much it is charred, whether it is toasted first.
Change one thing and you change everything, distillers said.
Brown-Forman is the only distillery that has its own cooperage and makes all its own barrels. (It used to make some for other distillers but business has grown so much Brown-Forman needs all the barrels for itself. In fact, the company is building a second cooperage in Alabama just to keep up with demand for its Jack Daniel's Tennessee Whiskey.)
"All of our color and 50 to 60 percent of flavor and aroma come from the barrel. You're going to let somebody else control that?" Morris said.
Every barrel of bourbon really does taste different.
When Morris samples his bourbon his cultivated taste buds can pick up an amazing range of flavors: everything from dark chocolate to peppercorn to leather to Earl Grey tea, citrus, bread pudding, apple pie, dark cherries, marzipan, anise, Christmas spices.
"You've got to dig through the caramel and the vanilla, the honey and sorghum," Morris said of bourbon's predominant flavors.
Even those distillers that buy barrels from, say, Independent Stave Co. in Lebanon or other cooperages, don't buy "off the rack." They specify exactly what they want in their barrels, from the tree to the finished product.
"We age the wood for nine months, but no less than one full summer. Wood cut in July has already part of missed one summer. So it has to go another year," Davis said of Maker's Mark's specifications.
"What we're doing is letting Mother Nature remove all the sap, remove the tannins. We just get the true essence, not the bitterness."
And not just any wood either. "We draw a line with the limestone shelf: the Ozarks through Kentucky to West Virginia," he said. "We are assured of the same limestone-like soil conditions."
And the char level. And the char on the barrel heads. And the number of staves per barrel. And the thickness of the staves. You get the picture.
Distillers are even more exacting about how those barrels are handled once they have the bourbon inside.
Some stack them in tall blackened rickhouses high on hills to maximize the weather fluctuations that drive the bourbon into the wood in the heat of summer and pull it back out in the winter.
The distillers have their favorite places to warehouse bourbon. Buffalo Trace master distiller emeritus Elmer T. Lee's signature bourbon comes from the sweet spot of floors 4, 5 and 6 of warehouses I and K at the Frankfort distillery.
"Generally speaking, I know where the best barrels are. ... The warehousing — that's where it gets its character, from the wood and the aging process," Lee said. "Got to have good wood."
Take Heaven Hill. It makes pretty much two bourbons — a wheated one for its Larceny or Old Fitzgerald and a regular one that could become Evan Williams, Elijah Craig or Parker's Heritage, depending on where and how it ages.
Some seek to control those effects. Four Roses uses a one-level warehouse; Maker's Mark rotates its barrels' locations to even out the changes that can occur. A barrel stored in the top of a warehouse will increase in proof; one stored in the lower levels will decrease in proof over time.
But others revel in the differences.
At Jim Beam's Clermont campus and scattered elsewhere across Kentucky, Beam has about 2 million barrels in storage at 50 warehouses at any given time, said Fred Noe.
That can give Beam a lot of variation to work with.
The skill is knowing which barrel needs to be bottled when, and with what other barrels.
"Once you bottle it," said Town Branch's Coffman, "you don't have a second chance."