Liquor is made by fermenting natural sugars into alcohol, then heating that liquid in a still to concentrate and purify the alcohol through distillation. Every spirit on the shelf, from vodka to whiskey to rum, follows this same basic sequence: prepare a sugar source, ferment it, distill it, and finish it. The differences between spirits come down to what you start with, how you distill, and what happens afterward.
It All Starts With Sugar
Yeast can only work with sugar, so every liquor begins with a source of fermentable sugars. For rum, that source is straightforward: sugarcane juice, sugarcane syrup, or molasses. Brandy starts with fruit, typically grapes. Tequila comes from the agave plant.
Grain-based spirits like whiskey, vodka, and gin take an extra step. Grains contain starch, not sugar, so they need to be milled and mixed with hot water in a process called mashing. Enzymes (often from malted barley) break those starches down into simple sugars that yeast can consume. Bourbon must be made from a mash of at least 51 percent corn. Rye whiskey requires at least 51 percent rye. Malt whisky uses at least 51 percent malted barley. Vodka can be made from virtually any grain, or even potatoes, since the goal is a neutral spirit with no distinctive flavor.
Fermentation Creates the Alcohol
Once the sugars are available, yeast is added to the liquid, now called a “wash” or “mash.” In the absence of oxygen, yeast consumes glucose and converts it into ethanol and carbon dioxide. This is the same biological process behind beer and wine, and it typically produces a liquid somewhere between 4 and 13 percent alcohol by volume, depending on the yeast strain and how long fermentation runs. Wine yeasts can push toward 11 to 13 percent. Most grain washes land closer to 5 to 10 percent.
That fermented liquid is essentially a rough, low-alcohol beer or wine. It contains ethanol, but also water, residual sugars, proteins, and hundreds of other compounds produced by the yeast. Distillation is the next step that transforms this into something recognizably strong.
Distillation Separates and Concentrates
Distillation exploits a simple physical fact: ethanol boils at 78.2°C (about 173°F), while water boils at 100°C (212°F). By heating the fermented liquid, alcohol vapors rise first, get captured, and are cooled back into liquid form. The result is a much higher concentration of alcohol than fermentation alone could produce.
There are two main types of stills. Pot stills are large, pot-shaped vessels, usually copper, that process one batch at a time. The still is filled, heated, emptied, then filled again. This method is slower and less efficient, but it preserves more flavor compounds from the original ingredients. Scotch whisky, cognac, and many craft spirits are made this way.
Column stills, developed in the 1830s, work continuously. They contain at least one tall cylindrical column divided into compartments by stacked plates. Liquid flows in and steam rises through, creating a continuous separation process. Column stills can distill to a much higher alcohol content and produce a cleaner, more neutral spirit. Vodka, most gins, and large-scale bourbon production rely on column stills. Some distillers use both types in sequence to balance flavor and efficiency.
Cutting Away the Dangerous Parts
Not everything that comes out of a still is safe or pleasant to drink. Distillers divide the output into three portions: heads, hearts, and tails.
- Heads (foreshots): The first vapors to come off the still contain the most volatile compounds, those with the lowest boiling points. This includes acetaldehyde, which has a pungent, metallic green-apple smell and contributes to severe hangovers, along with acetone and methanol. Methanol is particularly dangerous: it damages the liver and can cause blindness. Despite having a lower boiling point than ethanol, methanol clings to ethanol molecules and is notoriously difficult to separate completely, which is why the heads are discarded entirely.
- Hearts: This is the good stuff. The heart of the run is primarily ethanol with trace amounts of flavor compounds. This is the portion the distiller keeps.
- Tails (faints): As the run continues, heavier compounds with higher boiling points start coming through. These include fusel oils and a compound called furfural, derived from grains, which smells like burnt almonds. Despite its high boiling point, furfural doesn’t mix well with water and tends to vaporize earlier than expected. The tails taste harsh and oily, so they’re cut off as well.
Deciding exactly where to make these cuts is one of the most important skills in distilling. Column stills automate much of this process, while pot stills require the distiller to judge by taste, smell, and temperature. Some distillers run the hearts through a second or even third distillation to further refine the spirit.
Aging in Wood Barrels
Many spirits go straight from the still into oak barrels, where they may sit for years or even decades. Clear, raw spirit goes in; amber, complex liquor comes out. Whiskey, brandy, rum, and tequila (reposado and añejo) all require barrel aging. Vodka and most gins do not.
The barrel is not just a storage container. It’s a chemical reactor. When the wood is shaped into barrels, the inside is toasted or charred with fire, which breaks down three key structural components: lignin, hemicellulose, and cellulose. Over months and years of contact, the spirit extracts compounds from this treated wood. Lignin releases vanillin (the same compound that gives vanilla its flavor), along with related molecules that produce spicy and woody notes. Hemicellulose breaks down into sugars and phenolic acids, adding sweetness and complexity. Tannins from the wood create structure and astringency, similar to what they do in red wine.
American white oak, the standard for bourbon barrels, is particularly porous, which promotes the release of lactones that contribute coconut and vanilla aromas. Over time, the spirit also absorbs compounds like whiskey lactones, named for the role they play in shaping whiskey’s character. Other compounds, including a form of resveratrol and various phenols, increase in concentration the longer the spirit sits in the barrel. The interaction works both ways: the spirit also loses some of its harsher elements into the wood and through slow evaporation (the portion lost to the air is called the “angel’s share”).
Finishing and Filtering
Before bottling, many spirits undergo additional processing. One well-known technique is the Lincoln County Process, used for Tennessee whiskey. Fresh spirit is passed through a thick column of sugar maple charcoal before it ever enters a barrel. The charcoal works through adsorption, trapping larger molecules on its surface. Scientific studies have shown that this removes roughly a third of the harsh higher alcohols and nearly half of certain esters, producing a noticeably smoother, less aggressive spirit. The process costs about 1 percent of the alcohol content but adds no flavor of its own. It’s purely subtractive, smoothing rather than seasoning.
Chill filtration is another common step, especially for whiskey and vodka. The spirit is chilled to near freezing, which causes fatty acids and certain proteins to solidify so they can be filtered out. This prevents the spirit from turning hazy when a consumer adds ice or cold water, though some producers skip it deliberately, arguing it removes flavor along with the haze.
How Gin Gets Its Flavor
Gin follows a different path from most aged spirits. It starts with a neutral grain spirit, essentially vodka, then gets its character from botanical ingredients, primarily juniper berries along with any combination of herbs, spices, citrus peels, and flowers. There are two main methods for adding these flavors. In maceration, the botanicals are steeped directly in the neutral spirit, like making a strong tea. In vapor infusion, the botanicals sit in a basket above the boiling liquid so that rising alcohol vapor passes through them and picks up their aromatic compounds on the way to the condenser. Some distillers combine both techniques in a single run.
Setting the Final Strength
Spirits come off the still at varying strengths, often well above what you’d want to drink. Before bottling, distillers add water to bring the alcohol down to the desired level. In the United States, proof is simply double the alcohol by volume: a spirit at 40 percent ABV is 80 proof, and one at 45 percent ABV is 90 proof. The system varies by country. That same 45 percent ABV spirit registers as roughly 78.9 proof in Great Britain (which uses an older, gravity-based scale) and just 45 proof in France (where proof equals ABV).
By U.S. regulations, all whiskey and rum must be bottled at a minimum of 40 percent ABV, or 80 proof. Many cask-strength or barrel-proof releases skip the dilution step entirely, bottling at whatever strength the spirit reached during aging, sometimes 60 percent ABV or higher.