Alcohol is derived from the fermentation of natural sugars and starches found in plants. Yeast, primarily the species Saccharomyces cerevisiae (common baker’s yeast), consumes sugars and converts them into ethanol and carbon dioxide. This basic biological process is behind every beer, wine, and spirit, though the specific plant source varies widely depending on the beverage. A smaller share of the world’s ethanol is produced synthetically from petroleum-based chemicals, though this type is used for industrial purposes, not drinking.
How Yeast Turns Sugar Into Alcohol
The core chemistry is straightforward: yeast eats sugar and produces ethanol as a waste product. Saccharomyces cerevisiae is uniquely efficient at this, rapidly converting sugars to ethanol under almost any conditions, with or without oxygen present. This trait evolved independently in at least three different yeast lineages, suggesting it provided a strong survival advantage, likely by making the surrounding environment toxic to competing microorganisms.
For this process to work, the raw ingredient needs to contain sugar in a form yeast can access. Fruits like grapes already contain simple sugars, so fermentation can begin almost immediately once the juice is exposed to yeast. Grains like barley and corn, on the other hand, store their energy as starch, which yeast cannot directly consume. These starches must first be broken down into simpler sugars through a process called malting (soaking and germinating the grain) or by precooking before fermentation can begin.
What Each Type of Alcohol Is Made From
The plant source is essentially what defines most alcoholic beverages. Here’s how the major categories break down:
- Beer: Brewed from malted barley, sometimes with additions of rice or corn to supplement the sugar content.
- Wine: Fermented from grape juice. White wine uses just the juice, while red wine and rosé ferment from crushed whole grapes, including the skins. Wine can also be made from other fruits and berries, particularly in regions where grapes don’t grow well.
- Cider: Fermented from apples or pears.
- Whisky: Distilled from malted grains. Scotch malt whisky uses almost entirely barley, while other whiskies incorporate maize, oats, rye, and wheat.
- Rum: Distilled from sugar cane or molasses (a byproduct of sugar beet processing).
- Brandy: Distilled from fruit mash or wine. Cognac specifically comes from grapes, but other brandies use apples, pears, plums, pineapples, and strawberries.
- Gin and vodka: Distilled from grain or potatoes.
- Tequila: Distilled from a mash made from agave (often described as a cactus, though it’s technically a succulent).
The pattern is consistent: every drinking alcohol starts with a plant that provides sugar or starch. Distilled spirits simply add an extra step, heating the fermented liquid to concentrate the ethanol.
Byproducts Created During Fermentation
Yeast doesn’t produce pure ethanol. Fermentation also generates a group of compounds collectively called fusel oils, which include various heavier alcohols like isoamyl alcohol, isobutanol, and propanol. These occur naturally in all fermented beverages and contribute to flavor and aroma, but in higher concentrations they can cause headaches, nausea, and fatigue. Small amounts of methanol are also produced, particularly in fruit-based drinks. Distillation can concentrate or remove these byproducts depending on how carefully the process is managed, which is one reason why the quality of distillation matters so much for spirits.
Industrial Alcohol From Petroleum
Not all ethanol comes from plants. Since 1948, synthetic ethanol has been manufactured by combining ethylene (a gas derived from petroleum) with water in the presence of a chemical catalyst. This reaction takes place at extremely high temperatures (240 to 310°C) and pressures. The resulting ethanol is chemically identical to the fermented version but is used in industrial solvents, fuels, and chemical manufacturing rather than beverages.
In the United States, 94% of ethanol production is derived from corn, primarily for use as a fuel additive. Brazil, the other major producer, relies on sugarcane. There has been interest in cellulosic ethanol, made from non-food sources like corn stalks, wood chips, and switchgrass, but as of 2022 the U.S. had no commercial cellulosic ethanol production.
The Chemistry Behind the Name
In chemical terms, an alcohol is any organic compound with a hydroxyl group (an oxygen atom bonded to a hydrogen atom) attached to a carbon atom. You can think of it as a water molecule where one hydrogen has been swapped out for a carbon-based structure. Ethanol, the type in drinks, is the simplest common example, with just two carbon atoms. Methanol (one carbon) is the simplest alcohol overall but is toxic to humans.
The word “alcohol” itself has a surprising origin. It comes from the Arabic term “al-kuhl,” which originally referred to kohl, a fine powder used as eye cosmetic. When Latin speakers adopted the word, they used it for any fine powder. Over centuries, the meaning shifted to describe anything produced through a purification process, and by 1753, the first written record appeared using “alcohol” to mean the intoxicating ingredient in liquor. The popular claim that “al-kuhl” means “body-eating spirit” in Arabic is false.