Ethanol is also known as ethyl alcohol, “spirits,” or, even more frequently, simply alcohol. However, there are a great many alcohols, which is a generic term for organic compounds featuring the hydroxyl, –OH, group. Ethanol is a colorless liquid with a boiling point of 173°F (78.4°C). Because of the relative polarity of the –OH group, ethanol is capable of dissolving many inorganic ions as well as organic compounds.
Ethanol is a straight-chain alcohol with a molecular formula of C2H5OH and a structural formula. It is a primary end-product of anaerobic fermentation reactions by certain microorganisms, notably yeasts of the Saccharomyces species. See saccharomyces. In brewing beer, the smaller carbohydrates in wort, in particular glucose and maltose, are converted by yeast during fermentation to ethanol and carbon dioxide. Ethanol targeted for industrial use can be produced as a by-product of petroleum refining.
Ethanol is widely used to dissolve substances marketed for human consumption or contact, including flavorings, colorings, medicines, and perfumes. It is extensively used as a solvent and a reactant in processes in the chemical industries. It is a fuel and is now extensively used as an entire or partial replacement for gasoline in automobiles. It was first used for the latter purpose in 1908, with the Model T Ford.
The structural formula for ethanol was one of the first to be evaluated, in the mid-19th century. As long ago as 1828, Michael Faraday synthesized ethanol by acid-catalyzed hydration of ethylene, a route very similar to that used today to produce industrial ethanol.
Ethanol substantially reduces the surface tension of water. In wine this is responsible for the “tears” or “legs” phenomenon: following the swirling of wine in a glass, ethanol evaporates from the film on the glass surface, leading to an increase in surface tension of the liquid that runs down the glass in channels. The surface tension effect also underpins the observation that alcohol promotes foam formation in beer. However, alcohol destabilizes the foam once formed, as it competes with foam-stabilizing molecules in the bubble wall.
Alcoholic proof is a measure of how much ethanol is present in a mixture. It was formerly determined by adding alcohol in the form of liquor to gunpowder. The level of addition where the gunpowder just exploded was deemed “100 degrees proof.”
Ethanol reacts with carboxylic acids to produce esters, important flavor contributors in beer.
Oxidation of alcohol leads sequentially to acetaldehyde and acetic acid and is most important in living systems, including the human body, where it is catalyzed by the enzymes alcohol dehydrogenase and acetaldehyde dehydrogenase. Acetaldehyde is more toxic than ethanol and its accumulation may be the reason for many of the adverse impacts of ethanol. The reverse reaction whereby acetaldehyde is reduced to ethanol is the key final stage of alcoholic fermentation in yeast, a reaction that ensures the continuation of glycolysis.
Ethanol has a direct impact on the flavor of alcoholic beverages (warming) but also influences the volatility of other aroma compounds. It has psychoactive impacts, with a depressant impact on the central nervous system.
Ethanol is metabolized by the body—it is converted to acetyl CoA and is therefore a source of energy (calories).
The ethanol content of a beverage is usually measured in terms of the volume fraction of ethanol in the beverage, expressed either as a percentage (alcohol by volume, ABV, or alcohol by weight, ABW) or as alcoholic proof, in the case of distilled beverages.
Fermented beverages containing ethanol are made from diverse raw materials, the chief ones being grain (to produce beer), grapes (wine), honey (mead), and apples (cider). The range is further diversified if the base fermentation product is distilled. Thus, we have whiskies distilled from fermented cereal grains, brandies distilled from fermented fruit juices, rum distilled from fermented molasses or sugar cane, and vodka distilled from diverse start points from potatoes through grain. There may be further infusions with fruits and spices, e. g., gin or fortification of base fermentation products with distilled alcohol, e. g., port and sherry. Applejack is traditionally made by freeze-distillation of cider and the German eisbier in a similar manner from beer.
Oxidation of the alcohol in diverse fermentation products leads to acetic acid (vinegar). Ethanol is toxic to yeast and few yeasts will tolerate concentrations higher than 15% by volume.