How it Works
Distillation is the second major stage of spirits production, after fermentation. To distill something means to purify or concentrate it. In booze terms, this means taking a lower proof fermented beverage, such as wine or beer, and extracting only the alcoholic elements. This is easily done thanks to physics.
Alcohol (or more specifically, ethanol) boils at a lower temperate, about 175º F, than water, 212º F. So when a wine is heated to a temperature in within that range, the alcoholic molecules will vaporize while everything else remains a liquid. This alcohol-rich steam can then be collected and condensed back into a liquid, which will have a higher alcoholic content. Now it will be on its way to being brandy.
Of course, while the basic idea is relatively simple, in practice it is anything but. On this page, we'll dive into the nuts and bolts of distillation and the different tools and techniques employed along the way. Speaking of tools...
A basic example of a pot still.
"Distillation by Retort". Licensed under Public Domain via Wikimedia Commons
A spirit's flavor is determined by its congeners.
As explained on the fermentation page, about 75% of a fermented liquid, aka wash, is water and alcohol - both of which have no flavor. The remaining 25% is made up of a variety of organic chemical compounds such as alcohols, aldehydes, acids, esters, etc. These are collectively known as congeners. They are what provide alcoholic beverages with their flavors, both good and bad.
So while the central goal of distillation is to extract alcohol, an equally important task is navigating the congeners. A distiller needs to keep the ones they want and remove the ones they don't want (and in the right amounts) to achieve their desired flavor profile. They can't simply cherry-pick their favorites either. Congeners exist in different parts of a distillation batch, aka "run". Distillers choose congeners by keeping certain parts of the run and discarding (or recycling) others. So distillation is not really about flavor creation, but rather flavor separation.
3 Key Points to Remember:
1. How the congeners are separated depends on the type of still being used.
Pot Still: By Time
Column Still: By Position
Congeners all have different weights and thus will vaporize at different temperatures during distillation. How they are separated and selected by a distiller is different in a pot still than it is in a column still. Harold McGee explains it best - as he always seems to do - in his amazing book On Food and Cooking: "in a pot still, it’s done by time. In a column still, it’s done by position." I know that makes no sense now. Not to worry, more details are further down the page.
2. A spirit's proof coming off the still corresponds with its congener levels. And thus, flavor.
Higher Proof = Lighter Flavor
Lower Proof = Fuller Flavor
If a spirit comes off the still at a higher ABV it will be purer in alcohol (ethanol) and have relatively fewer congeners, meaning it'll have relatively less flavor. On the flip side, a spirit that comes off at a lower proof will have retained more congeners and, naturally, be more flavorful. To two prime examples: vodka, which is flavorless by design, is typically distilled to 94% ABV, and cognac, which is jam-packed with flavor, is never distilled higher than 72.4% ABV.
To be clear, less flavorful doesn’t mean the spirit is inferior in any way, nor does more flavorful mean superior. It's just a question of a spirit's style. Note, this fact about proof does not apply to bottles of booze at the liquor store. Nearly all spirits are diluted with water after before they are bottled, so the proof on their label will not be an indicator of congener content.
3. "Reflux" is key to quality distillation, and spirit purity.
Reflux is a phenomenon that happens inside a still. It refers to the repeated cycle of molecules (water, ethanol, and congeners) vaporizing, condensing, and vaporizing again before exiting the still. It essentially means redistillation.
Reflux cleanses the distillate of more congeners and leads to a greater extraction of alcohol, resulting in a more refined spirit. So the more reflux there is - as in, the more times this cycle of vaporizing and condensing is repeated - the purer and cleaner a spirit will be.
Different stills produce different levels of reflux, and all good spirits require some reflux. However, at certain levels the amount of reflux becomes stylistic choice.
The Pot Still
How it Works
The pot still is the prototypical design of the still and was the only way to make spirits for the first 1500 years (give or take a few centuries) of their existence. It is essentially configured as a kettle with a tube sprouting out of the top. The basic process is very simple:
The fermented liquid, aka "wash" or "mash", is placed in the pot.
The pot is heated to somewhere between 175º F and 212º F, vaporizing only the alcohol.
The alcoholic steam rises up and flows into the tube which is called a lyne arm or swan's neck.
The lyne arm runs through the condenser which is often cooled by being submerged in water.
This cools the steam and condenses it back into a liquid, which is now much higher in alcohol content.
The newly concentrated "spirit" then drips out of the still and is collected. (Incidentally, the word distill comes from the Latin word "distillare" which means “to drip down”.)
After one run through a pot still, a spirit’s strength will be about 20-25% ABV, this is often referred to as the "low wines". A second, or sometimes even third, run is needed to get the spirit to an ideal 65-85% ABV (which will be diluted with water before bottling, of course).
Separation by Time
The run of a pot still, which, again, means it's output, is categorized into three sections: the heads, hearts, and tails. These make up the beginning, middle, and end of the run, respectively. Each stage is characterized by what types of congeners the distillate contains. This is what I meant above when I said the congeners in a pot still are separated by time.
Making the Cut
The part of the run that is selected for aging or bottling is called the cut, which is determined by the distiller. Sometimes they will keep the just hearts, other times a bit of the heads and tails will be retained to give a spirit a more flavor and character. It all depends on the type and style of spirit being made. A quality pot-still spirit is like a quality cut of meat, it requires a quality butcher.
The Three Stages of a Pot Still Run
1. Heads (and Foreshots)
The foreshots are the very first vapors to come off the still and are always discarded. The rest of the heads contain large amounts of higher alcohols and off-tasting congeners, such as the toxic methanol, acetaldehyde - which is often blamed for hangovers - and acetone, which smells like paint thinner. Much of the heads are discarded. However, there is some good stuff worth retaining, notably esters, which are fruity, floral compounds. You can read more about them here.
This is the good stuff. The hearts are primarily ethanol and largely congener free. This is the purest, cleanest, and safest to drink part of the run.
3. Tails (Feints)
The tails, aka feints, are lower in alcohol and high in heftier congeners like fusel oils and fatty acids. Much of the tails are discarded, though some distillers rely on them for their oily texture to give a spirit more body. They also contain certain compounds which can assist in developing desired flavors during barrel maturation. Additionally, tails are rich in phenols, which among other things, are the compounds responsible for smoky aromas. For this reason, more tails are retained by distillers who make single malt scotch and mezcal.
Spirits that are made in a pot still:
Single Malt Scotch - Must be made pot still.
Cognac - Must be made in pot still.
Most high-quality tequilas and just about all mezcals.
Many fuller bodied aged rums.
A More Artisanal Method, But is it Better?
Many still view the pot still as a superior method of distillation, particularly for fine barrel-aged spirits. One reason for this is pot-distilling is a slow, linear process, which gives distillers more hands-on control of the congener selection. Also, pot-distilled spirits generally retain more congeners than column-distilled spirits, particularly heavier ones. This is why you can count on spirits made in a pot still to generally be fuller flavored, which can mean rich and decadent, or rustic and rough around the edges. Again, it's not about good or bad, just the desired flavor profile.
I personally don't feel that pot stills are universally better than column stills, but there is no question that a large chunk of the world’s best spirits are indeed pot distilled. Though I'll also point out that many of those spirits are required to be pot-distilled by law.
Disadvantages of a Pot Still
A pot still has a few operational drawbacks. For one, it is far less efficient at extracting alcohol than a column still, as we'll see below, and thus they produce less volume. They also take much longer to operate, and the still needs to be cleaned after each run. In effect, making pot-distilled spirits is much more time consuming, and thus, much more expensive.
The Importance of Copper
Pot stills are usually made from copper because is a superior heat conductor and stips out unpleasant sulfurous congeners. This is possible because copper reacts with sulfur compounds to form copper sulfate, which will stick to the inside of the still and effectively be removed from the distillate.
How a Pot Still's Shape Influences Reflux and Flavor
When selecting or constructing a pot still, a distiller will consider a myriad of factors such as size, shape, and height, which will all have a bearing on what kind of congeners are captured, the amount of reflux created, and how the spirit ultimately will taste.
Generally shorter, squatter stills will capture more heavy congeners and induce less reflux because vaporized molecules don't have to travel as far to reach the lyne arm. This produces fuller bodied spirits. Tall, narrow stills produce relatively lighter spirits because fewer congeners can make it all the way to the top before condensing and falling back into the pot. This creates more reflux and excludes more congeners, thus producing a lighter spirit. The angle of the lyne arm will have an impact on these factors as well.
Even seemingly minor details like how the still is heated - directly or indirectly - and how the vapor is condensed - tubes or a worm - will extert an influence on the distillate.
A More Efficient Method
The column still made large scale distillation possible. To quote Paul Pacult, "a column can do in 12 hours what a pot still can do in a week."
Not only are they faster, but they encourage much more reflux allowing them to produce spirits that are exceptionally pure and clean tasting, far beyond what is possible in a pot still no matter how many runs you do. So for lighter style spirits like vodka, grain whiskey, and certain styles of white rum, a column still is essential
Flexibility to Make a Wide Variety of Spirits
Columns stills are not only useful for making make lighter spirits at high volumes. There are plenty of complex, full-bodied spirits made in column stills such as Bourbon and Armagnac. Like pot stills, column stills are wholly customizable, Some have multiple columns, some just one. For a fuller bodied spirit that comes off at a lower ABV, a column might only have 4-6 plates. For one making the purest highest ABV spirit possible, it will have 50-60.
On top of that, a distiller has the option of opening some of the plates and allowing the vapor to bypass them without condensing. They could even bypass a whole column. This offers great flexibility and autonomy. As Dave Broom notes when discussing a particular column still in his 2003 book “Rum”: “a distiller can make a huge number of marks [styles] with this system. In Guyana, for example, D.D.L. [a distillery] makes nine different marks on its three column stills.”
Spirits that are typically made in a column still:
Lighter style rums.
Grain whiskey for blended scotch, Canadian, and Irish whiskey.
Most large scale American whiskeys - bourbon and rye.
Armagnac - usually made in a hybrid still, see below.
This diagram shows the journey the wash/vapor takes inside a type of column still called a coffey still (aka patent still), named after its inventor Aeneas Coffey. It has two columns: the analyzer (column A) which heats and separates the alcoholic vapor, and the rectifier (column B) which cools and condenses it.
"Column still" by Karta24 (talk) - Own work - Création personnelle.
Licensed under GFDL via Wikimedia Commons
Column B: Rectifier
Column A: Analyzer
The wash enters a tube which runs through the rectifier.
Steam is injected into the analyzer.
The heaviest elements are drawn off and discarded.
Alcoholic vapor rises through the plates and heads to the rectifier.
The molecules that condensed lower down in the rectifier are rerouted back to the analyzer for another go round.
Lightest, most volatile molecules are drawn off.
The spirit is collected!
As distilling technology has improved, the still has become a much more pliable tool, and the line between the pot and column styles has become increasingly blurred.
Case in point, nowadays many distillers and use what’s called a hybrid still, which is composed of a pot with a column on top, or connected to it. This allows for great versatility. It can be run with the efficiency of a column still but gives a distiller the option of opening up all, or some, of the plates so the vapor flows unimpeded making the still behave more like a traditional pot. These types of still are especially useful for craft distillers who are making small batches of multiple styles of spirit. They are redefining how stills are thought of as we know it.
Hybrid Still. A pot combined with a column.
Pot vs Column - Is One Better?
No. Both stills can be used to make excellent spirits, as well as substandard ones. It can be tempting to broadly characterize pot-distilled spirits as heavier and more complex and column still spirits as often lighter and purer, but that's oversimplifying things.
Sure, there are examples that support this generalization. For instance, the best tequilas are made in a pot still, whereas lower quality mass-market brands generally use column stills. I'm not saying every type of spirit could be replicated on any type of still, it’s not that black and white. Each still has its pros and cons.
The type of still used by a distiller - pot, column, or hybrid - will depend on the style of spirit being made, the legalities governing that spirit’s category, and the commercial size of the distillery. But regardless, in the end, quality will always rely on the skill of the distiller and the quality of the base ingredients, not from the still itself.
Pot vs. Column
A "still" is the instrument used to conduct distillation. There are two basic types: the pot still and the column still. The pot still is the basic, traditional model - you can see a crude example of one above - while the column still is more industrial, complicated, and capable of much higher volume. Broadly speaking, pot stills are used produce spirits that are fuller - both in flavor and body - whilst column-distilled spirits are tapped for purer, lighter, and cleaner tasting spirits. One still better than the other - despite what some may claim. They have different strengths and serve different purposes. In fact, today many craft distillers use what's called a hybrid still, which blurs the line between the two and offers benefits of both. On this page, we'll examine how both stills work and how they differently shape a spirit's flavor. But first, let's look at where a spirit's flavor actually comes from...
One notable, and brilliant, facet of this model is the tube with the wash runs through the rectifier first, before entering the analyzer to be distilled. This kills two birds with one stone. It pre-warms the wash and helps to cool and condense the alcoholic steam already flowing through the rectifier. Both save energy and expedite the process.