clock menu more-arrow no yes mobile

Filed under:

An Absurdly Complete Guide to Understanding Whiskey

If you buy something from an Eater link, Vox Media may earn a commission. See our ethics policy.

Everything anyone could ever want to know about whiskey and why it tastes the way it does.

What really makes whiskey taste like whiskey? If flavor truly just came down to a simple formula of distilling ratios of grains plus time spent in a barrel, then there wouldn’t be an infinite range of tastes, profiles and qualities. There’s a world of whiskey geekdom to explore, all of the finer points which turn that basic math into the highly complex art and science of whiskey production.

Aging & Warehousing

Age is just a number, and the amount of time spent in a barrel is far from the only factor the affects a whiskey's final flavor.

Temperature & Weather

The external climate where a whiskey is warehoused greatly impacts how rapidly it ages, how much interaction it has with the wood from the barrel, and how much evaporation takes place. The hotter the temperature, the more alcohol penetrates the wood of the barrels, and the thirstier the angel's share. Add humidity to the heat, and evaporation quickly escalates.

The seasonal temperature fluctuation in, say, Kentucky allows barrels to "breathe" in and outcontracting in the cool of the winter, and expanding in the heat of the summerwhereas the steadier weather in Scotland offers far more year-round climate consistency. "We have a very mild, temperate climate in Speyside," explains The Macallan brand ambassador Craig Bridger. "You don't have the extreme swings of temperature you get in Kentucky. There's not a lot of variance for us."

The Father of Japanese Whisky had spent time living and learning in Scotland, and had a clear vision for how he would craft his own whisky, on his own island, halfway around the world.

Masataka Taketsuru, founder of Japan's Nikka Whisky, chose the location of his Yoichi distillery in the Hokkaido Prefecture because of the region's similar weather conditions to Scotland. The Father of Japanese Whisky had spent time living and learning in Scotland, and had a clear vision for how he would craft his own whisky, on his own island, halfway around the world.

Sometimes climates of choice or oceanside environs aren't available, as is in the case for Jefferson's Ocean Aged At Sea. So, the brand sends its whiskey traversing the globe aboard ships, and it's exposed to salty ocean air as it sways and sloshes. Meanwhile, Taiwan's Kavalan has garnered worldwide acclaim while aging its whiskies for a fraction of the period that its Scottish competitors do, thanks to their hot, humid climate.

Type of Warehouse

A visitor to Wild Turkey in Kentucky may get a chance to hear master distiller Eddie Russell wax poetic on the company's warehouses. They control every detail, from the materials used for construction, to the exterior paint color of the building, the location of the building (atop a hill or in a valley beneath one), how much direct sunlight it receives, temperature control (only opening windows in summer and closing them in winter), and their preference for metal-sided warehouses.

Visit Woodford Reserve and hear master distiller Chris Morris wax poetic to a different tune. "There are two styles of maturation, unheated or heated, as different as night or day," he explains. Woodford prefers to heat cycle their warehouses, controlling the internal temperature rather than letting the external environment take charge. Their warehouses are constructed of brick, stone or, for newer buildings, insulated concrete. This approach allows for more micromanaging of the aging process, as opposed to willfully succumbing to the whims of the weather.

The way barrels are stored also plays a role. Frederick Stitzel invented what would become the modern style of barrel warehousing, patenting an "improvement in racks for tiering barrels" in 1879. Storing barrels in this manner, with a thin plank of wood supporting each end of a horizontally aligned barrel, rather than a solid wooden platform or floor, allows the entire exterior surface to be exposed to the elements, turning a regular warehouse into today's rickhouse.

Internal Location

It's not just the geographic location of a warehouse, or the type of warehouse that matters, but the internal location within that warehouse where the barrel is stored. The top of a warehouse receives higher temperatures, resulting in a whiskey which ages far more rapidly.

Different floors within a warehouse, different sides of the building and specific row locations all impart unique characteristics based on temperature, airflow, humidity and other factors. "Every building has its own personality, every floor has its own personality," says Morris.

Moving barrels from one location to another, or incorporating barrels from different areas of a warehouse into a blend, greatly impacts its flavor. At Maker's Mark, for instance, the brand follows a schedule where all barrels are aged on the top floor of a warehouse for three summers, before rotating to the bottom floors for approximately three to four more years. When Jim Beam Black went NAS, Fred Noe began incorporating younger whiskey from the top floors of their warehouses to compensate.

Think that's specific? Read up on Buffalo Trace's experimental Warehouse X, where their mad whiskey scientists are testing endless warehouse variables.


Clearly, the way barrels are stored impacts the whiskey being made. The type of barrels utilized also plays a huge role.

Barrels aging in Scotland. Shutterstock: Pawel Kowalcyk


Size is the most obvious variable to barrels, and there's a wide range. Simply put, the size of a barrel determines the level of exposure a spirit has to the wood. Smaller barrels impart faster aging, although many question the quality of the aging produced in less time by small barrels, due in part to a lack of seasonal breathing (mentioned above) and other longterm climate and environmental conditions.

Size is the most obvious variable to barrels, and there's a wide range.

The standard across major American whiskey producers is the 53-gallon barrel. Many of the newer, smaller producers across the country though utilize 30-gallon barrels or even smaller sizes to help them age their wares in less time. Consider that along the back shelf of your favorite cocktail bar, there may be a barrel aged cocktail sitting pretty in a mini 1-gallon barrel.

Across the whiskey industry there are sherry butts, which hold approximately 132 gallons, Hogsheads, rebuilt barrels used in the Scotch industry which are approximately 60 to 65 gallons in size, and many other specific shapes and sizes.


Jerry Maguire once said that his "word is stronger than oak." But was he talking about American oak, French Limousin oak, Spanish oak, or Japanese Mizunara oak?

Wood from different regions will directly impart different flavors to a spirit. Suntory Whisky chief blender Shinji Fukuyo credits Mizunara casks for producing the "distinctive Japanese" long, spicy finish, for instance. There are more specific, regional differences as well, with American oak from Minnesota showcasing distinct characteristics comparative to American oak sourced from the middle of the country, or from the east coast.

Different woods have different compositions, with more porous woods allowing spirits to penetrate deeper into the barrel. For whiskey students looking for their whiskey geek PhDs, consider whether wood sourced from dense forests which had survived for hundreds of years would impart the same qualities as wood sourced from only decades-old forests planted and cultivated by humans, even when the exact same species of tree is being used, grown in exact same place.

Wood from different regions will directly impart different flavors to a spirit.

Was the atmosphere and environment which the tree was a part of fundamentally different versus now? What about the overall temperature and climate, the particles in the air from nearby industry or a lack thereof? Do 200 years of seasons and weather innately impact a wood compared to just 20 years?

Most believe the answers to these questions to be yes.


Barrel char is created just as one would expect, with bursts of open flame torching the exposed surface of the wood on the inside of a barrel.

By definition, bourbon must be aged in new charred American oak barrels. Even most whiskey novices grasp that whether or not a barrel is charred impacts a spirit's flavor. In this case, the charring process is what enables the vanillin compounds within the wood to provide bourbon's signature vanilla and caramel sweetness. There's a range of chars available though, numbered to denote distinct stages. Wild Turkey, for instance, is one of many producers who uses the deepest char, #4, which yields a characteristic "alligator char," the inside of the barrel reminiscent of an alligator's scaly skin. Barrels may also be toasted to different levels, generally using dry heat as opposed to open flame, separate from or in addition to the charring, imparting still different qualities. The Brown-Forman Cooperage utilizes a proprietary toasting system based upon radiant heat.

New vs. Used

As mentioned above, by law bourbon is aged in new charred American oak barrels. But why "new"?

A new barrel, or virgin barrel, is one which has never been used to age a spirit. This type of barrel would impart stronger charred elements and flavors than a barrel which is being reused and has already soaked up whiskey for years.

The Scotch industry primarily uses ex-bourbon barrels, as well as ex-sherry barrels, some of which were specifically "seasoned" with sherry for the sole purpose of eventually aging whisky. First-fill barrels, which have only been previously used once, second-fill barrels, previously used twice, and those used repeatedly beyond that, all offer varied levels of their original flavors.


Staves are the individual pieces of wood used in the construction, or "raising" of a new barrel, and they too play a role. For example, the Brown-Forman Cooperage raises a barrel with between 31 to 33 staves of different widths.

Beyond sizing, there are other characteristics to consider as well. For instance, was the grain cut to produce the proper grain profile? Were the staves heated, or naturally aged or "seasoned" in the elements, and if so, for how long?

At Maker's Mark, they season their staves for nine months, including a full summer, helping to produce peak levels of vanillin compounds. To produce Maker's Mark 46, they insert 18-month-old seared French oak staves into a barrel for an extra eight to 11 weeks of aging, only performed in colder months of the year.

Woodford Reserve ages their wood outdoors for nine months before toasting it, and finally charring it. "We can pre-set certain flavors deep into the wood that charring alone can't do," explains Morris. Meanwhile, at The Macallan, Bridger notes that they dry age their staves for up to two years.

Production Control

While much of the industry has faced barrel scarcity issues due to an array of factors including extra demand, a re-burgeoning housing market, not enough loggers hacking away and detrimental weather, certain companies produce their own barrels, or tightly control the process. This helps them achieve their own exacting standards, while ensuring the supply is never caught off.

Brown-Forman has their own cooperages, producing nearly 3,500 barrels a day for their brands, including Jack Daniel's and Woodford Reserve, while The Macallan has their own "master of wood," Stuart MacPherson, who oversees their entire regimented process of production. "We own those casks from the beginning," says Bridger, allowing them fine-tuned control over the wood and the barrels.

The Formula

Grain + yeast + water = whiskey. That simple equation though includes infinite room for variation, experimentation and refinement.


Clockwise from top left: Barley, wheat, corn, rye. Photo: Shutterstock/anmbph

Mash Bill Specifics

The mash bill of a whiskey is the ratio of grains it includes. Bourbon must incorporate a minimum of 51 percent corn, rye must utilize at least 51 percent rye grain, and different types of whiskey have other requirements. The mash bill for a single malt Scotch is by definition 100 percent malted barley.

From there though, brands are free to go in their own directions. Bourbons traditionally incorporate three grains: corn, rye and malted barley. A simplified explanation offers corn as the base, rye as providing extra flavor, and malted barley providing the enzymes to feed the fermentation process.

Distilleries today are experimenting with everything from oats to triticale, quinoa to millet, and a range of other grains to produce new whiskey riffs.

The ratio of these grains though varies heavily, and wheat may also be used in place of rye. A "high rye" bourbon will impart more spice from the rye grain into the whiskey, while "wheated" bourbons offer softer palates, and are in high demand in the wake of the Pappy craze.

But even then, not all rye or barley is equal. For instance, many companies utilize very specific, and in some cases, exclusive or proprietary grains. For instance, at Maker's Mark, they don't just incorporate wheat, but rather soft red winter wheat. Even the milling techniques utilized impact the end result, offering a different consistency or mix of grain sizes.

Distilleries today are experimenting with everything from oats to triticale, quinoa to millet, and a range of other grains to produce new whiskey riffs.


Enter the hallowed ground of any distillery and the yeast strain used for fermentation will undoubtedly be cited as one of that brand's special characteristics. "Our yeast is very important to our flavor profile," says Morris, touting yeast strain "Woodford Reserve 78B" as he cites what is an oft-repeated theme from one company to the next.

At Wild Turkey, the same yeast has been utilized for more than 50 years, and was formerly kept at master distiller Jimmy Russell's house. Every week, the company makes the yeast from scratch starting in a Petri dish. At Jim Beam, their yeast dates back to 1935. Jim Beam himself used to drive back home after a day at the distillery with his carefully protected yeast sitting in the front seat of his Cadillac with him. At Maker's Mark, the same Samuels family yeast strain has been maintained over the decades, and is grown every day.

Fermentation length also will impart different qualities, with longer fermentations producing more esters, and therefore fruitier characteristics. At Woodford Reserve, the brand follows a six-day fermentation process, which is perhaps the longest of any distillery the world over, and far longer than the average two to three day fermentation.

Water Supply

Ask a Manhattanite, or anyone from the tri-state area, and bagels just aren't quite right beyond New York. The same principle follows whiskey around the world, too.

If a visit to Kentucky offers a chance to talk aplenty about yeast, that discussion still pales compared to talk of the famous limestone water supply. The mineral content of the water offers a distinctive taste, and is one of the key reasons why bourbon became permanently rooted in the Bluegrass State.

It's not just bourbon and Kentucky though. In Japan, Suntory's distilleries were located precisely for their pure water supplies, both designated by the Japanese government as amongst the "most precious" water sources in the country, created by "the filtration of rain and snow through thousand-year-old granite rocks."

Islay pot stills. Photo: Shutterstock/Jaime Pharr

Peat & Smoke

Many aspects of the whiskey the world knows today were not created by scientists in white lab coats refining exacting formulas— although that's happening now—but instead by happenstance. Rye whiskey was dominant in America as rye grain was available in the eastern United States. As the country moved west and corn was grown, corn was used instead, and it became the backbone of bourbon.

Many aspects of the whiskey the world knows today were not created by scientists in white lab coats ... but instead by happenstance.

In Scotland, prevalent peat bogs provided a heat and energy source. Peat fires were used to heat the stills, and more importantly, peat fires were used to dry the malted barley. Hence, the peat profile of Scotch, particularly Islay Scotch, was born.

Today, different grain smoking techniques are becoming more prevalent, from the highly touted Corsair Triple Smoke, which incorporates not only peat, but beechwood and cherrywood smoke, to Virginia's Copper Fox Distillery, which utilizes applewood and cherrywood in their production process.


Distilleries have to control what part of the distillate actually makes it into the barrel. The liquid flowing from the still can be broken down into what's known as heads, which are poisonous, hearts, which is the cleanest, tastiest portion, and tails, which begin to impart reduced quality of flavor.

How tight or loose a distiller is with his cuts directly changes the raw spirit that fills the barrel. For instance, The Macallan is famously tight with their cuts, incorporating only 16 percent of the distillate.

The proof that a distiller chooses to distill to also imparts different qualities. "We feel like we're cooking it medium rare," says Russell, meaning they leave more flavor in the distillate as opposed to a "well done" distillate at a higher proof.


"The magic a particular distillery has, you'll never be able to recreate it," says Bill Thomas, proprietor of noted whiskey bar Jack Rose Dining Saloon in Washington, D.C., and foremost, a hardcore whiskey geek. "All of these factors came together and were magic for a period of time."

He's talking about everything already covered so far, barrels and warehouses, fermentation and yeast and mash bills and the rest, along with what remains, the stills themselves. "You could take the same mash bill, the same grains in perfect percentages, and the same yeast strain," he wagers, "but with a different still, the whiskey may be similar, but it might not even be close."

Distillation Type

Distillation may be performed by a pot still, or a column still. The former is traditional, completed on a batch by batch process, the latter, also known as a continuous still, more efficient and able to be operated without the need for batches. Beyond the choice of pot stills or column stills, a distillery may choose to double distill their whiskey, as is classic but not required for Scotch, or triple distill, as is the norm for Irish whiskey. Woodford Reserve's Morris uses an Irish style triple distillation pot still process, whereas massive columns rule the day at the Jim Beam American Stillhouse, with 200 gallons per minute sent to a six-story high still.

Shapes & Sizes

Even stills of the same class will churn out juice far different depending on other characteristics, such as the size of the still, its specific shape, the size of its different components such as the neck or line arm, how many plates are utilized, how they're heated, what they're made from, and more.

The Macallan's "curiously small stills" are the smallest in Speyside, but are still substantially larger than much of those used by today's new generation of American distillers. As The Macallan expands production, it's not with bigger or different stills, but with an ever-increasing number of exact replicas of the stills already in usage.

"They'll be carbon copies," confirms Bridger, "that's one thing we would be absolutely loathe to change in any way." Similarly, the ongoing expansion at Maker's Mark is introducing exact replicas of their own stills, preserving what they call their specific "microenvironment."

Suntory Whisky takes a far different approach, their three distilleries operating all types of pot stills of various shapes and sizes, enabling them to produce over 100 malt whiskies. As opposed to blended Scotch whisky, which sources single malts and single grains from many different distilleries, Suntory distills all of the individual whiskies used in one of their blends themselves.


Finally, Starbucks Is Going to Bargain With Its Unionized Workers

James Beard Foundation Awards

James Beard Foundation Awards 2024: Winners, News, and Updates

Awards Season

The 2024 James Beard America’s Classics Winners Are Here