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Distillation Glossary: Pots, Columns, and a Bucket of Tails
Today we're continuing our cocktail glossary series with a look at some of the terms used in distillation, focusing on a set of basic terms used to describe the act of distillation and the two types of stills used to make virtually ever spirit available on the market. Not certain what the difference is between a pot still and a column still? We'll get you sorted out.
Distillation is the process of separating a liquid or vapor mixture into its component parts, through vaporization and condensation. You can also think of distillation as a process of purifying a liquid.
Distillation is necessary for a number of industries, not just beverage alcohol. Oil refining, perfume making, and production of chemical products such as turpentine all use distillation. Obviously, those uses of distillation are not the focus of this column, so let's move right along...
For the purposes of distilling beverage alcohol, the basic process goes like this:
- Start with a fermented alcohol product: beer (or, more accurately, wash) or wine, usually.
- Heat the liquid. Alcohol boils at a lower temperature than water, so it will turn to steam before the water does, and rise up in the still.
- Collect the vapors of alcohol.
- Chill them, so they turn back into liquid.
- Collect the alcohol from the still.
Of course, the daily practice of distillation is more complicated than that, especially when it's done by professionals working with complex equipment. But as I describe each type of distillation in detail, I'll fill in some of the blanks the above steps leave out.
A device used for the distillation of alcohol.
A pot still is a type of still used for distilling certain types of alcohol—notably, single-malt Scotch, Cognac, mezcal, and funky rums. To simplify, the general process is this: the wash (for whiskey) or wine (for brandy) is heated in the pot. Vapors containing alcohol and some of the water rise up to the head, a cap on the top of the pot that captures the rising steam; the steam is drawn off into a tube called an arm. From the arm, the vapors travel to a coil, or "worm", immersed in a tub of cold water. The water chills and condenses the vapors back into liquid, in this case mostly of alcohol. The alcohol is removed through a spout attached to the end of the worm; from here, the alcohol usually flows directly to a second still for another distillation, but in some cases, it's taken from the still immediately and aged in barrels.
Pot stills can be as small as a countertop appliance, or large enough to hold thousands of gallons of wash or wine.
Making booze using a pot is called batch distillation, because only one batch of distillate can be made at a time, and the still needs to be taken off-line and cleaned between batches.
Also called a continuous still, a patent still, or a Coffey still, a column still is used mainly for making white spirits, such as vodka, gin, or some rums, in addition to bourbon, rye, and much of the Armagnac that's produced. (Cognac, on the other hand, uses pot stills.)
A column still doesn't work by directly heating the wash, as a pot still does. The wash enters the still through an injection point on the side of the column. Hot steam rises up from the bottom and intersects the wash streaming down from the injection point. As the wash hits the hot water vapor, the steam strips the ethanol from the wash and they rise up the column together.
The still is filled with a series of plates or other packing materials that separate the still into chambers. Each chamber functions as a miniature version of a pot still. So as the mix of ethanol and steam rises into a new chamber, it undergoes continuous stages of distillation, and each time the mixture rises up into the next chamber, it contains a higher concentration of ethanol. After it reaches the top of the still, it's drawn off and condensed.
A column still can produce a much purer distillate than a pot can. Pots can achieve up to 50% alcohol by volume or so; a column can reach 95%. For this reason, and because column stills can run indefinitely, without needing to be cleaned, they're far more efficient at making spirits. However, the spirits they make tend to lack the character of those distilled in pot stills.
Foreshots / Heads / Middle Run (Hearts) / Tails
We're not talking about flipping coins here. These are terms of art for various stages of the distillate as it comes off the still. Note that these terms apply mainly to distillate made in pot stills. Operators of column stills usually use fractionalization to remove unwanted elements from booze.
The foreshots, as you might guess, are the first parts of the distillate. They're high in such poisonous stuff as methanol and acetone, plus esters and aldehydes that make for untasty hooch. These are discarded.
Heads are the next parts of the distillate, and can be kept or discarded, depending on the distiller. They're high in ethanol, but also in the congeners that give a spirit flavor, aroma, and character.
The middle run, or hearts, consist of all the distillate you keep and (sometimes) age before bottling. The balance of alcohol and congeners is pretty much in keeping with how booze should taste.
Tails are the last bits out of the still. They're low in ethanol and high in congeners, and although they're not harmful, they don't taste like anything you'd want to drink.
What other distillation terms are you curious about? We'll follow up in more detail soon...
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