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Ethanol (CH₃CH₂OH), the active ingredient in alcoholic drinks, for consumption purposes is always produced by fermentation – the metabolism of carbohydrates – by certain species of yeast in the absence of oxygen. The process of culturing yeast under alcohol-producing conditions is referred to as brewing. The same process produces carbon dioxide in situ, and may be used to carbonate the drink. However, this method leaves yeast residues and on the industrial scale, carbonation is usually done separately.

Drinks with a concentration of more than about 50% ethanol by volume (100 US proof) are flammable liquids and easily ignited. Some exotic drinks gain their distinctive flavors through intentional ignition, such as the Flaming Dr Pepper. Spirits with a higher ethanol content can be ignited with ease by heating slightly, e.g. adding the spirit to a warmed shot glass.

In the liver, the enzyme alcohol dehydrogenase oxidizes ethanol into acetaldehyde, which is then further oxidized into harmless acetic acid by acetaldehyde dehydrogenase. Ethanol is metabolized into acetaldehyde and then into acetic acid. Acetic acid is esterified with coenzyme A to produce acetyl CoA. Acetyl CoA carries the acetyl moiety into the citric acid cycle, which produces energy by oxidizing the acetyl moiety into carbon dioxide. Acetyl CoA can also be used for biosynthesis. Acetyl CoA is an intermediate common with the metabolism of sugars and fats, and it is the product of glycolysis, the breakdown of glucose.

When compared to other alcohols, ethanol is only slightly toxic, with a lowest known lethal dose in humans of 1400 mg/kg (about 20 shots for a 100 kg person), and a LD₅₀ of 9000 mg/kg (oral, rat). Nevertheless, accidental overdosing of alcoholic drinks, especially those of concentrated variety, is a risk, especially for women, lightweight persons and children. These people have a smaller quantity of water in their bodies, so that alcohol is diluted less. A blood alcohol concentration of 50 to 100 mg/dL may be considered legal drunkenness (laws vary by jurisdiction). The threshold of effects is at 22 mg/dL.

Alcohol affects the gamma-aminobutyric acid (GABA) receptors, to produce a depressant (neurochemical inhibitory) effect. Alcohol is similar to other sedative-hypnotics such as barbiturates and benzodiazepines both in its effect on the GABA_A receptor although its pharmacological profile is not identical. It has anxiolytic, anticonvulsant, hypnotic and sedative actions similar to many other sedative-hypnotic drugs. Alcohol is also cross-tolerant with benzodiazepines and barbiturates.

Excessive consumption of alcohol leads to a toxication-induced delayed poisoning called hangover (in Latin, crapula refers to intoxication and hangover). Various factors contribute, including the toxication of ethanol itself to acetaldehyde, the direct toxic effects and toxication of impurities called congeners, and dehydration. The hangover starts after the euphoric effects of alcohol itself have subsided, typically in the night and morning after alcoholic drinks were consumed. However, the blood alcohol concentration may still be substantial and above the limits imposed for drivers and operators of other dangerous equipment. The effects of a hangover subside over time. Various treatments to cure hangover have been suggested, many of them pseudoscientific.

In chemistry, alcohol is a general term for any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom, which in turn may be bound to other carbon atoms and further hydrogens. Other alcohols such as propylene glycol and the sugar alcohols may appear in food or beverages regularly, but these alcohols do not make them “alcoholic”. Methanol (one carbon), the propanols (three carbons giving two isomers), and the butanols (four carbons, four isomers) are all commonly found alcohols, and none of these three should ever be consumed in any form. Alcohols are toxicated into the corresponding aldehydes and then into the corresponding carboxylic acids. These metabolic products cause a poisoning and acidosis. In the case of other alcohols than ethanol, the aldehydes and carboxylic acids are poisonous and the acidosis can be lethal. In contrast, fatalities from ethanol are mainly found in extreme doses and related to induction of unconsciousness or chronic addiction (alcoholism).

Source: http://en.wikipedia.org/wiki/Alcoholic_beverage

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