Alcohol distillation is the process of separating alcohol from a fermented liquid by heating it until the alcohol vaporizes, then cooling that vapor back into a concentrated liquid. It works because ethanol (drinking alcohol) boils at roughly 78°C (173°F), while water boils at 100°C (212°F). By carefully controlling temperature, a distiller can capture alcohol-rich vapor and leave most of the water behind, producing spirits far stronger than beer or wine could ever reach through fermentation alone.
How the Science Works
Fermentation produces a liquid called a “wash” that typically sits between 5% and 15% alcohol by volume. Distillation concentrates that alcohol by exploiting the 22-degree gap between ethanol’s boiling point and water’s. When the wash is heated past 78°C, ethanol begins to vaporize more readily than water. That vapor rises, gets channeled into a cooling apparatus, and condenses back into liquid form with a much higher alcohol concentration than what you started with.
There is, however, a hard ceiling. Ethanol and water form what chemists call an azeotrope at about 95.6% alcohol by volume. At that concentration, the two liquids behave as a single substance and vaporize together at the same rate, meaning no amount of simple redistillation will push the purity higher. This is why even the strongest grain alcohol you can buy tops out around 95% ABV. Getting beyond that requires specialized chemical techniques outside of standard distillation.
Pot Stills vs. Column Stills
The two fundamental still designs produce very different spirits. A pot still is the older, simpler approach: you fill a large copper vessel, heat it, collect the vapor, empty the spent liquid, and start over. It’s a batch process. Each run produces a relatively low-proof spirit that retains a lot of flavor compounds from the original wash. Whiskey, brandy, and rum distillers often favor pot stills precisely because of that richness.
Column stills, by contrast, are tall cylindrical towers that can run continuously without stopping to refill. Vapor rises through a series of perforated plates inside the column, and at each plate, the vapor gets a little purer. The result is a much higher-proof, much cleaner spirit. Vodka is the classic column-still product, distilled to 95% ABV or above where nearly all flavor compounds have been stripped away. Column stills also offer more consistency from batch to batch, since the separation between different fractions of the distillate happens more automatically than with a pot still.
The Condenser: Turning Vapor Back to Liquid
Once alcohol vapor leaves the still, it needs to be cooled and collected. The oldest condenser design is the worm tub: a long copper coil submerged in a vat of cold water. As vapor spirals through the narrowing coil, it gradually condenses. Worm tubs produce a heavier, more full-bodied spirit because the vapor has relatively little contact with the copper surface. Volatile sulfur compounds survive the journey, giving the final spirit oily, sometimes meaty or rubbery character that mellows with aging.
Most modern distilleries switched to shell-and-tube condensers starting in the 1960s. These push the vapor through many small copper tubes surrounded by cold water, maximizing copper contact and stripping out heavier compounds. The result is a lighter, cleaner new spirit. A handful of Scottish distilleries still use worm tubs specifically because they want that distinctive weightier character in their whisky.
Making the Cuts
Not everything that comes out of a still is safe or pleasant to drink. A distillation run produces four distinct fractions, and knowing where to “cut” between them is the core skill of distilling.
- Foreshots (first 1-2%): The earliest vapor contains methanol, which boils at 64°C, along with acetone and harsh aldehydes. This fraction smells like nail polish remover and is always discarded.
- Heads (next 5-10%): Still sharp and solvent-like, containing acetaldehyde and ethyl acetate. Most distillers discard this or set it aside.
- Hearts (middle 60-70%): This is the good stuff. Primarily ethanol with a balanced mix of flavor compounds. This fraction becomes the finished spirit.
- Tails (final 20-30%): As the ethanol runs out, heavier compounds dominate: fusel oils like propanol and butanol, fatty acids, and increasing amounts of water. Tails taste oily and unpleasant on their own, but many distillers save them to redistill in the next batch.
In a pot still, the distiller decides these cuts by monitoring temperature, tasting small samples, and using experience. In a column still, the cuts happen more automatically thanks to the physics of the column plates, though operators still fine-tune where the boundaries fall.
What Gives Each Spirit Its Character
Pure ethanol is flavorless. Everything interesting about a spirit comes from the small percentage of other volatile compounds, collectively called congeners, that survive distillation alongside the ethanol. The most abundant are higher alcohols, followed by esters (fruity, floral notes), acids, and aldehydes. The distiller’s choices about how much of the heads and tails to blend into the hearts fraction directly shape the flavor profile.
This is why distillation proof matters so much. The higher you distill, the more congeners you strip away. U.S. regulations reflect this reality. Bourbon must be distilled at 160 proof (80% ABV) or below, preserving grain character. Vodka must be distilled at 190 proof (95% ABV) or above, deliberately eliminating flavor. Brandy sits in between, with “neutral brandy” defined as anything distilled above 170 proof but below 190. Whiskey of any type must stay below 190 proof, because once you cross that line, you’ve technically made neutral spirit rather than whiskey.
Why Copper Matters
Nearly every traditional still is made from copper, and this isn’t just tradition. Copper actively reacts with sulfur compounds in the vapor, binding them to the metal surface and removing them from the spirit. A still with more copper contact produces a lighter, cleaner distillate. A still with less copper contact, like one using a worm tub condenser, lets more of those heavier compounds through. Distillers manipulate this variable deliberately. The shape of the still, its height, and the type of condenser all control how much copper the vapor touches on its journey from liquid to liquid again.
Single vs. Multiple Distillations
Many spirits go through distillation more than once. Most Scotch single malt is distilled twice in pot stills, with each pass increasing the alcohol concentration and refining the flavor. Some Irish whiskeys are triple-distilled, producing a notably smoother spirit. Each additional pass strips away more congeners, so the number of distillations is a deliberate trade-off between smoothness and complexity. Column stills effectively perform many “distillations” in a single pass, since each plate in the column acts like a miniature redistillation step. A tall column with dozens of plates can achieve in one continuous run what would take many separate pot still batches.