Drinking alcohol is ethanol, a simple molecule made of two carbon atoms, six hydrogen atoms, and one oxygen atom (chemical formula: CH₃CH₂OH). It’s produced when yeast consumes sugar and converts it into ethanol and carbon dioxide, a process called fermentation. Every alcoholic beverage, from beer to whiskey, starts with this same basic reaction. What differs is the source of sugar, how the liquid is processed afterward, and what else ends up in the final product.
How Yeast Turns Sugar Into Alcohol
Fermentation is the engine behind every alcoholic drink. Yeast cells, particularly strains of Saccharomyces cerevisiae, eat simple sugars like glucose and fructose and produce ethanol as a metabolic byproduct. This isn’t incidental. Yeast generates ethanol specifically to recycle a molecule called NAD+, which the cells need to keep breaking down sugar for energy. Carbon dioxide is released at the same time, which is why fermenting liquids bubble and why beer and champagne are naturally carbonated.
What makes this process remarkable is that yeast will ferment sugar into ethanol even when oxygen is available. As long as there’s plenty of glucose around, the yeast defaults to alcohol production. Fermentation typically continues until the sugar runs out or the alcohol concentration rises high enough to kill the yeast, usually somewhere around 14 to 18 percent alcohol by volume depending on the strain.
Where the Sugar Comes From
The raw material determines the type of drink. Fermentation occurs naturally in any sugar-containing liquid from fruit, berries, honey, or tree sap, but commercial production uses more controlled sources. These fall into two broad categories: things that already contain sugar and things that contain starch, which must be broken down into sugar first.
- Grapes are the most common fruit used for alcoholic fermentation. The species Vitis vinifera is selected specifically because of its high sugar content at maturity, making it ideal for wine. When that wine is further distilled, it becomes brandy.
- Corn is the most important grain used as a fermentable starchy cereal and serves as the base for bourbon and much of the neutral spirit produced in the United States.
- Barley is malted (allowed to partially sprout) to activate enzymes that convert its starch into sugar. It’s the foundation of beer and Scotch whisky.
- Sugarcane and its products, including cane juice and molasses, are used to make rum throughout the tropics and semitropics.
- Agave provides the sugars for tequila and mezcal, with tequila legally required to be produced in Mexico under Mexican law.
- Potatoes, cassava, and other starchy roots and tubers are also used, particularly for vodka in parts of Eastern Europe.
For starchy raw materials, an extra step is needed before yeast can do its work. Enzymes, either naturally present in malted grain or added separately, break long starch chains into simple sugars. Only then can fermentation begin.
Distillation: Concentrating the Alcohol
Fermentation alone can only produce drinks up to roughly 15 to 20 percent alcohol. To make spirits, the fermented liquid is distilled. This works because ethanol boils at about 173°F, well below water’s boiling point of 212°F. When you heat a mixture of the two, ethanol vaporizes more readily. That vapor is captured, cooled, and condensed back into liquid with a much higher alcohol concentration.
In practice, distillers use columns with internal plates or packing material that force the rising vapor and falling liquid to mix repeatedly. At each stage, more alcohol evaporates out of the liquid and more water condenses out of the vapor. This “fractional” distillation can push alcohol concentration up to about 95.6 percent, the practical maximum. Most spirits are then diluted back down with water before bottling.
U.S. regulations require all distilled spirits to be bottled at a minimum of 40 percent alcohol by volume (80 proof). Vodka must be distilled to at least 95 percent before being diluted. Whiskey, by contrast, must be distilled at less than 95 percent to retain flavor from the grain, then aged in oak barrels. Gin starts as a neutral spirit that gets its character from juniper berries and other botanicals during or after distillation.
Water: The Largest Ingredient
The biggest component of most alcoholic drinks isn’t alcohol. Beer is 90 to 96 percent water, with the remainder being ethanol and flavor compounds. Wine is roughly 85 percent water. Even an 80-proof spirit is 60 percent water. The quality and mineral content of the water used in production directly affects the taste of the final product, which is why many distilleries and breweries emphasize their water source.
Congeners: The Flavor Compounds
Ethanol and water make up the bulk of any alcoholic drink, but the character comes from congeners, a catch-all term for the hundreds of other compounds produced during fermentation and aging. These include higher alcohols, esters, aldehydes, and acids, each contributing distinct flavors and aromas.
Esters are the largest class of aroma compounds in spirits. Researchers have identified over 140 individual aroma compounds in some distillates, with 74 of them being esters alone. These form when higher alcohols react with acids, producing flavors that range from fruity to floral. One compound, 2-phenylethanol, contributes a flowery, honey-like note. Others, like 3-methyl-1-butanol, add the pungent, solvent-like quality sometimes described as “fusel.” Hexanol brings grassy and green notes, while a compound found in trace amounts in melon spirits produces a distinct cucumber-rind flavor.
The raw materials matter here too. Many of these higher alcohols form from amino acids in the original grain or fruit. Valine in the mash produces isobutanol. Leucine produces the fusel alcohol 3-methyl-1-butanol. Phenylalanine produces the floral 2-phenylethanol. This is why drinks made from different base ingredients taste fundamentally different even before aging enters the picture.
Darker spirits like bourbon and red wine tend to have higher congener concentrations than clear spirits like vodka, which is deliberately distilled to near purity and then filtered.
Additives and Preservatives
Beyond what fermentation and aging naturally produce, many alcoholic beverages contain intentional additives. Sulfur dioxide is one of the most important. It’s widely used in winemaking as both an antibacterial agent and an antioxidant, and UK breweries are permitted to use it in beer at up to 70 milligrams per liter. Sorbic acid is another preservative allowed in wine to prevent bacterial and mold activity.
Vodka can legally contain up to two grams per liter of sugar and up to one gram per liter of citric acid. Flavored spirits, vermouths, aperitifs, and liqueurs often include essential oils extracted from herbs and spices, along with synthetic flavoring compounds and coloring agents like caramel. Caramel coloring is common in whiskey and rum to ensure visual consistency between batches.
Clarification is another standard step. Wines and beers are filtered to remove cloudiness caused by suspended proteins, yeast, and other particles. Various fining agents are used to bind to these particles and pull them out of the liquid before bottling.
What Makes Ethanol Different From Toxic Alcohols
Ethanol is the only alcohol that’s safe to drink in moderate amounts. Methanol, which differs by just one carbon atom, is extremely dangerous. As little as 10 milliliters can cause blindness, and 30 milliliters can be fatal. Methanol isn’t actually a byproduct of yeast fermentation. It forms when pectin in fruit breaks down, which is why fruit-based spirits require careful distillation to separate it out. Isopropanol, the alcohol in rubbing alcohol, is a three-carbon molecule that’s toxic when ingested. The structural differences are small, but the way your body metabolizes each one makes all the difference. Your liver converts methanol into formaldehyde and formic acid, both of which destroy tissue. Ethanol, by contrast, is broken down into acetaldehyde and then acetic acid, which your body can process and clear.