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How Flavour is Created in Whiskey

If you have read our Intro to Whiskey article then you know that there is an incredibly wide range of flavours that can be found in the various whiskies1 from around the world2. But have you ever wondered how flavour is created in whisky? How do you get all of those incredible flavours in the glass? This is the question that we will explore in this guide.

More specifically, we’ll look at the whiskey making process, and dive deep into malting, the mash, fermentation, distillation, and aging, and how all of these steps present unique options and choices for distillers who want to infuse different flavours.

Article Overview

  • Ingredients of Whiskey
  • Malting
  • Mashing
  • Fermentation
  • The Types of Whisky Stills
  • Aging
  • The Importance of Water in Whisky Making

Whiskey Ingredients

There are precious few ingredients that go into making whiskey:

  • Malted (or unmalted) grain (barley, corn, rye, wheat, etc.)
  • Water
  • Yeast

And that’s it! So, again, how can there possibly be flavours that range from citrus fruit to crème brûlée, from vanilla to iodine, from juicy sultanas to charcoal smoke?

How Grain Affects the Flavour of Whiskey

Let’s start with the grain.

Obviously, there will be different flavours present depending on what grain is chosen. I am sure that if you took a bite of corn followed by a mouthful of barely, you’d able to tell the difference, right? So that part is fairly straightforward. However, distillers aren’t using juicy, fresh corn on the cob. Instead, they’re grinding the dried corn up and soaking it in water.

With that in mind, let us explore that rather basic process of making whiskey before we dive into how all these wonderful flavours appear. 

Malting Starts the Process of Turning Starch into Sweet Sugar

At the start of the whiskey making process, the grain is soaked in water and then spread out on the floor of the malting barn to dry and germinate. This is known as ‘malting.’

While whiskey can be made from barley, corn, rye, or wheat, we’ll use barley as the example here as the grain of choice.

Drying the barley – Image courtesy of Warminster Malting Ltd, https://www.warminster-malt.co.uk/

Traditionally, people would walk through the malting floor and toss the barley into the air to ensure that the temperature does not get too hot. This ensures that the enzymes that have been activated in the malting process are not destroyed. This is important because these enzymes are hard at work turning the starch in the barley into sugar (remember those sweet flavours we mentioned?). To make sure the enzymes stay active the temperature needs to remain below 20 degrees celsius (we are Canadian…so yes, Celsius) otherwise the enzymes get too hot and stop this process.

What does malting the barley actually accomplish? 

Malting is a highly controlled process in which the cellular structure of the barley is altered to the desired specifications that allow for fermentation to take place4.  This is done in three stages.

  1. Steeping: This process combines the barley and water together at a specific and controlled temperature that will initiate germination, the natural process of the seed undergoing changes to reproduce itself.
  2. Germination: Despite triggering germination, we don’t want a barley plant to sprout, we want whiskey. So the malters speed up the germination process over 4-6 days at a controlled temperature between 16-20 degrees Celsius. During this stage the cell walls along with the proteins are degraded to the point where starch-degrading enzymes can access the starch granules. This is important later, so remember this bit.
  3. Drying: Next, the malt is kilned which stops the germination process5, dries the barley, and is then milled into smaller particles for the mashing stage.

The malt that has been created during this process is all done so that the yeast that will be added later for fermentation has the necessary nutrients to thrive…namely fermentable sugars and free amino nitrogen.6

How Smokey Flavour is Added to Whiskey: Introducing Peat to the Malting Process

Now if you want to add smoke and peat to the flavour, like most Islay whiskies, it is now that you would add peat to the drying process. The dried peat is burned and the smoke flows over the drying barley, infusing it with the smoky flavours.

Mashing Pulls More Sugar and Liquid is Removed from Grain

After malting, the barley has been through a pretty dramatic cellular change: All the stored starch that is kept inside the husk that allows the barley to reproduce itself have been accessed and has started to be turned into sugars.

These grain needs to be crushed into a fine grist. Like with coffee grinds, how fine the grist is can slightly affect the flavour, so this is another conscious choice by the distilleries and another way that different flavours can be imparted into the whiskey.  

Mashing is a crucial step, and it is all about the conversion of starches into sugars, by adding hot water to the grist, which at this point is now called the mash. This is a very precise process. If the temperature is too low, the enzymes won’t activate and too high, and the enzymes break down before they can get to work.

The hot water starts at just below 70 degrees and works up towards boiling. The liquid (wort) is then removed from the grain (now called draff) and is ready for the next step.

The Importance of Water

Let’s talk about water for a second. As Lew Bryson, senior drinks writer for The Daily Beast and full-time writer about beer and spirits since 1995 said in his book Whiskey Master Class:

“Water is essential to making whiskey, but it’s not a huge factor in flavor creation. It’s more like a factor that can only make whiskey flavors terrible, unless you get it right.”

One of the main considerations when distilleries are choosing their water source is that it be free of iron. Iron in the water will “turn the whiskey black and make it taste wretched.”7 This is why many distilleries rely on iron-free water sources, like the many lakes here in Canada, the free-flowing springs in Scotland, the mystic wells in Ireland, and the limestone water in Kentucky.  There are other “earthy” notes that can appear in water (like the smell after it rains), and distillers are very aware of this and ensure it is filtered out before the water is added to the mash.  

Fermentation: The Most Critical Stage in Whiskey Production

Now, our wort is cooled and then placed into washbacks.

Washbacks are tall, circular vessels used in distilling to ferment wort. They vary in size and shape, but their most important feature is their size: washbacks must be large enough to hold thousands of litres of wort with extra space above the liquid for the mixture to foam up as the yeast expels carbon dioxide. They can be made out of wood or stainless steel.

And this is where the magic starts to happen: This is where all those sugars we have been talking about are about to get eaten by a living organism that we intentionally dump into the wash.

It’s time to get geeky about YEAST!

Yeast The Powerhouse Behind Whiskey and All of Its Many Flavours

What exactly does the yeast do? Well, once added to the wash, it begins feasting on the sugars and proteins, while excreting alcohol, carbon dioxide, and small amounts of flavourful esters and other flavour-building chemicals, such as fatty acids, all while reproducing itself every twenty or so minutes.

Without yeast, there is no alcohol, no flavour, and no whiskey.

As Jonny McCormick stated in his article The Feast from the Yeast in the Malt whiskey Yearbook 2020,

“We owe yeast a debt of thanks. This plucky, self-sacrificing single cell is the powerhouse that produces not only all the alcohol in whiskey, but also a feast of delicious aromatic and flavoursome congeners that whiskey connoisseurs find pleasurable. Trust me, fermentation is the most critical stage in whiskey production.” 

Image courtesy of blog.distiller.com

This sentiment is echoed by Don Livermore, the master blender for Hiram Walker & Sons. Livermore has measured the concentration of various flavour chemicals, called congeners, in new and maturing spirit. His research confirms that the highest concentration of congeners comes from yeast and not from grain.

Livermore has used gas chromatograph mass spectrometry (GCMS)8 to sort the various congeners derived from fermentation into two groups: those that originate in the grain and those created by the yeast. With this information he has been able to identify the source of flavours in whiskey and has created a very detailed flavour wheel (see below). All this to say…we all need to pay more attention to yeast.

The Whiskey Flavour Wheel

Since yeast is the catalyst in creating our favourite beverage, one might think that there would be a wide variety of sub-species that are used to bring about different flavours. However, in general, that is not the case. Most distillers use the same strain of Saccharomyces cerevisiae yeast.

Don’t worry about how to say it, just know that that is the type of yeast that almost all whiskey makers use and is commonly referred to as distillers yeast. And for the most part, since the 1950s, the major whiskey distilleries in Scotland and Ireland have used the same strain of Saccharomyces cerevisiae

For an industry that prides itself on producing unique flavours, this certainly seems like an oversight. It was done because yeast strains can mutate quickly while they are feeding on the sugars during the fermentation process and could bring unwanted flavours into the whiskey.

To avoid this, and the potential loss of an entire batch of whiskey, distillers stuck with what worked: A stable strain that produced expected results over time. There are some distilleries doing some interesting experiments with different stains of yeast9, but for the purpose of this article, we will keep it moving.

Fermentation Continued: Temperature, Yeast and Flavour Profiles

Ok, back to the main attraction. Yeast needs sugar and water. Once the mash has been cooled10 the yeast can be added to get the alcohol producing process started. Since this is a heat producing chemical reaction, the temperature needs to be closely observed to ensure it doesn’t get too cold or too hot. Too cold and the yeast gets stunted, too high, and the yeast will eventually die…but not until some unwanted flavours and aromas creep in. You can see why deviating from what you know works is risky. If you experiment with your yeast you could end up with a batch that smells like vinegar and pickles11…and wouldn’t that be a terrible waste?

But what flavours does yeast actually impart into the “soon-to-be” whiskey? Remember that flavour wheel I mentioned? Livermore’s flavour wheel is divided into three sections; yeast, wood, and grain. 

As you can see, yeast can imbue a wide range of flavours, from sulfuric notes like a newly struck match to fruity notes like sweet apples. Sour vinegar to green hay. Lavender to mild wax. This is an incredible range of aromatics and flavours that, for so many whiskey drinkers, come from either a complete blind spot in the flavour generating process, or at best, an afterthought. Yeast really does deserve equal credit along with the grain and the wood used for the casks when it comes to flavour generation.

Sadly, this amazing process comes to an end after a mere 48 hours as the yeast has consumed all of the sugars and multiplied to the point where there is not enough food left in the wash for it to consume, and it dies.12 What you have now is somewhere between an 8-10% beer…which I can say I do enjoy, but that’s not what we want. We want whiskey. How do we get there?

Distillation: Stills Literally Help Shape the Taste

Now it’s time to turn that beer into whiskey. This process is called distillation and comes down, once again, to science. There are three main goals in this process. 

  1. Concentrate the alcohol by removing the water.
  2. Remove any unwanted compounds / aromas etc.
  3. Retain all the flavours we have been working so hard to create up to this point

Let’s break this down and tackle these one at a time.

How do you separate the water from the alcohol to increase the alcoholic concentration? You boil it. And this works because of a basic scientific principle. Alcohol (ethanol) boils at 78.4 degrees Celsius (or 173.1 degrees Fahrenheit) while water boils at 100 degrees Celsius (212 degrees Fahrenheit). This is pretty straight forward, and even I understand this one.

The liquid is then put into pot stills, large (normally) copper stills that in the case of whiskey tend to have a swan neck design. The specific design can affect the flavour, so distilleries ensure that all of the stills they use for any specific whiskey are the same to ensure the flavour remains identical. 

The purpose of the still is to vaporize the alcohol so it raises above the water and passes over cool copper wires which returns the vapour into liquid. After one run through the still the liquid contains about 20% alcohol by volume (ABV).

How Different Types of Whiskey Stills Affect Flavour

The main types of stills that are used to concentrate the alcohol and retain the flavours are pot stills and column stills. Each has their own pros and cons, and which is used is a conscious decision by the distiller and yet another factor in flavour creation.

So let’s spend a bit of time on these before we move on. If you want to watch a great video from one of our favourite duos on Youtube, Whiskey Tribe, they made a very good concise explanation that goes over both pot still and column stills.

Pot Stills: The Whiskey Purists’ Choice

Traditionalists will claim that the only “real” way to make whiskey is by using a pot still. This is the way it has been done in Scotland for hundreds of years, and since that is the birthplace of whiskey1, that must be the “right” way. But we aren’t overly concerned about right and wrong, just how each still helps with the flavour creation process. So let’s put aside what is “best” and instead focus how each one works.

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Pot stills at Bunnahabhain

Copper pot stills work much the same as a pot, hence the name2. If you boil water in a pot, the lid will have water droplets on it when removed. This occurs when the steam hits the lid and cools down, turning the vapour back into a liquid.  The same principle applies to pot stills when boiling the wash when trying to separate water and the alcohol. The wash is brought to a boil, the vapour rises and hits the “lid”, is cooled down, which transforms the vapour back to liquid, which now has a much higher alcohol concentration (now somewhere between 20-25%) than when the process was started (between 7-15% in the beer).

The geometry of the still is important. For vapour to reach the curved neck (called the lyne arm) and escape the still, the neck needs to be fully heated so that the vapour doesn’t cool down and fall back into the still. The still is gradually heated so that the liquid will boil, rise, condense, and fall back and repeat the process a couple of times to get as much impurity out of the liquid as possible. This process is called reflux. Once this has happened the still will be heated and the vapour will be allowed to escape. But not all the vapour. Remember that alcohol and water boil at different temperatures? Of course you do. So only the alcohol vapours will escape and the heavier water will fall back down into the pot.

But this is only half the story. These aren’t just pot stills, they are copper pot stills! This is very important, because, once again, science. Copper reacts with the sulfur in the vapour that is left overs from the grains, and creates copper sulfates. These stay behind in the pot and the spirit is allowed to be purified. But there is no way that hundreds of years ago the Scots knew all of this right? Well, likely not. They made their stills out of copper because it was there and it was easily malleable. What a great historical stroke of luck. 

Column Still: Lighter, Thinner, Less Oily Flavours

So while the purists will always argue that pot stills are the only way to go, we don’t hold our noses up in the air here, so let’s explore what column stills are and how they impact the flavour that ends up in the bottle. 

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Column still courtesy of https://alcademics.typepad.com/.a/6a00e553b3da20883401910480fd4d970c-pi

Column stills are mainly used in the production of American bourbon and can crank out much more volume.  For this reason, they are also used in a lot of blended whiskey as the volume produced is much higher than single malt whiskey. The basic principles and goals remain as with the pot still: Heat the wash to the point where evaporation occurs, remove the impurities, capture the alcohol. 

What a column still does incredibly efficiently is removing the impurities, so much so that column still whiskies have a much lighter taste and feel than those made with traditional pot stills.

How Column Stills Work 

Column stills are, in essence, a continuous distillation system that can operate, well, continuously. This is why they can outproduce pot stills. They are constantly being fed with the beer from the wash and it is constantly coming out the other end as the refined spirit (which is now called low wines).  

The column is composed of a series of copper plates or trays. The beer (wash) is fed into the column at about the vertical halfway point. The beer runs down through the trays of the column due to gravity. At the same time steam is being blasted up from the bottom of the column. When the steam comes into contact with the beer, it volatilizes the ethanol and flavor components. As a result, these vapors begin traveling back up through the plates.3

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Image courtesy of https://shop.distillery-equipment.com/products/26-gallon-moonshine-still-with-4-borosilicate-sight-glass-4-plate-column

Vapor to Liquid and Repeat

Thanks to basic geometry, each tray is slightly cooler than the one beneath it. This causes a bit of condensation of the vapors on each tray. Since hot vapors are constantly coming through the system, those condensed vapors are redistilled and thrown back into a vapor state. This rapid transformation from vapor to liquid to vapor happens over and over again. This reaction increasingly separates heavier compounds like fusel oils from the lighter compounds like ethanol as the vapors make their way up the column. As a result, this increases the “purity” of the spirit. If there are enough trays in place, column still distillation can produce a spirit over 96% ethanol.

As the spirit makes its way through the column, eventually it will reach a point where the distiller is ready to draw it off from the still. But remember: these vapors are still hot, so we need to condense them into liquid form. What some distilleries do is set up the incoming feedstock piping to run in a counterflow to the outgoing vapors. The hot vapor piping then passes heat onto the feedstock piping, thus cooling the spirit down to a liquid while preheating the incoming feedstock. It’s an energy-efficient and environmentally friendly system.

Because of the efficiency of column stills they produce a lighter, thinner, and less oily flavour profile than pot stills because they can filter out the heavier flavour notes very quickly because of the multiple copper plates that the vapour is continuously passing over. 

Heating: Direct Fire vs. Steam and the Affect on Flavour

So that’s the container, but what about the heating and cooling? 

Does this make a difference?

Absolutely it does.

Originally, the pot stills were all heated the same way: Stick some wood under it and start a fire. This is called direct fire for obvious reasons.

Of course an open wood fire under a pot may not be the ideal method, so different methods have been experimented with over the years, including the burning of coal, oil, and even natural gas.  Direct fire is much harder on the copper pots, both inside and out. 

But we are concerned with taste, so let’s focus on the inside. 

When the fire heats up the copper pot, the sugars in the beer start to caramelize on the inside of the pot. Since we’ve spent so much time cultivating these sugars to get the flavour into the whiskey, we don’t want to lose them now. So distillers came up with a solution by way of a copper arms that would scrape coiled copper nets (called rummagers) along the bottom of the pot still to scrape the caramel so that it remains in the wash and its flavours stay in the whiskey. Many distilleries have moved away from direct fire to steam to heat the wash, but some have stuck with the direct fire method because of the caramelization that occurs and the flavours this imparts.

Cooling: Shell and Tube Creates Lighter Flavour

Just like heating, how the wash is cooled can also impact the flavour. There are two basic methods for this process, which is known as condensing and the tubes used are called condensers. 

The two types are (see pics):

  1. Worm tubes
  2. Shell-and-tube

Worm tubes look like what their name suggests, a coiled copper tube that is immersed in cold water. Worm tubes work more slowly and have less copper exposure, which leads to a heavier spirit where some of the sulphur notes are retained.

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Worm Tube pic courtesy of https://www.scotchandscones.com/ancnoc-highland-single-malt-worm-tubs/

The shell-and-tube method has hundreds of small copper tubes that turn back and forth inside the shell. There is cold water running through the tubes while the vapour from the pot still is in the shell. This exposes the vapour to much more copper and will cool the vapour much more quickly and efficiently. This leads to a lighter flavour as the process removes the sulphur notes.

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Shell tube courtesy of https://prohibitionuniversity.com/category/distillery-marketing/


The liquid is then placed into oak barrels where it mellows and obtains colour from the oak.

The final ABV depends on what the distillery wishes to put out. If they want a lower ABV, they may add water to, well, water it down.

You may also see some bottles with the label “Cask Strength”, which means that the whiskey was not watered down and you are getting the liquid as it was straight out of the barrel. These always have a much higher ABV3. Once the aging is done, the whiskey is bottled and is ready to enjoy. 

Simple Processes Plus Conscious Choices Equals Complex Flavour

So now you know the process that goes into actually making whiskey.

There are not many steps and it’s incredible that so many different flavours can end up in your glass when the ingredients are just grain, water, and yeast.

But at each step, the distilleries are making conscious decisions that affect the final outcome. Where do they get their water from? Is the peat locally sourced or not? What strain of yeast are they using? What type of oak barrel do they use? Is it a first fill or was something else previously aged in the barrel? All of this will change the final product that ends up in your glass.

How do you get apples into the flavour, vanilla, iodine, bicycle innertube? Well, this is a complicated science that goes beyond the six steps covered above.

Disclaimer: I am not a scientist

Ok dear reader, I have a Masters degree in International Relations, which is about as far from chemistry and microbiology as it can get. So while I’m going to be dropping some science here, I am no expert and am relying heavily on the work of people that understand this stuff and have spent many years going to school or interviewing those people to get at what is happening at the molecular level. I have given credit throughout so check the endnotes below, if you love this stuff and you can find where I got this info.


  1. Whether you spell it whiskey or whiskey, you are talking about the same liquid. The different spelling simply denotes where in the world it came from. Since The Whiskey Geeks has an “E” in it, we will be spelling it with an E in this article.
  2. And if you haven’t read it, well, now you know that there are a wide range of flavours that can be found in whiskies from around the world!
  3. The highest we have personally tried was a whopping 64.5%ABV.
  4. We are not scientists, but we do know how to give proper credit where it is due. We obviously didn’t do this research but you can find the source information which was published in the Scientific Journal Starch in Food 2nd Edition: Structure, Function and Applications at https://www.sciencedirect.com/topics/food-science/malting#:~:text=Malting%20is%20a%20controlled%20germination,and%20kilning%20to%20dry%20it
  5. Because we don’t want more barely…we want WHISKEY!!!
  6. Told you we were going to seriously geek out 🙂
  7. Whiskey Master Class, page 65.
  8. SCIENCE!!!!!
  9.  If you want to really dig in deep on the yeast, The Feast from the Yeast in the Malt whiskey Yearbook 2020 goes into more detail and is a very interesting read.
  10. Remember the mash had to get heated close to to get those enzymes working from the paragraph above?!
  11. I mean, I like pickles, but not in my whiskey.
  12. Pour one out for the yeast. You did great.
  13. We here at The Whiskey Geeks come from a Scottish background, so while there is some debate between Scotland and Ireland as the birthplace of whiskey, we are giving the win to the Scots 🙂 
  14. Once again, shout out to  Whiskey Master Class, chapter 7. Tons of great information and if this is super interesting to you, we highly suggest you pick up this book and read it. It gets The Whiskey Geeks double thumbs up.
  15. Being totally honest, this was tough to wrap my head around. So I found this amazing article https://blog.distiller.com/column-still-distillation/ and used this section from it. If you want to learn more about column stills check out the article.

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