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Methanol

metanol (ES)
méthanol (F)
metanolo (I)
metanol (PO)

Monohydric alcohol (also carbinol, methyl alcohol, wood alcohol, wood spirit) is a colourless, burning-tasting liquid with an unmistakable, sweetish odour. Although it differs significantly from ethanol (drinking alcohol), it can hardly be recognised in terms of taste due to superimposition with other aromatic substances in alcoholic beverages. The ancient Egyptians already produced methanol by pyrolysis (splitting of organic compounds by high temperatures from 200 °C) of wood and embalmed their dead with a substance mixture. The name "methylene" was given to it in 1834 by the French chemists Jean-Baptiste Dumas and Eugène-Melchior Péligot; it is composed of "méthy" for wine and "hylé" for wood. Methanol itself is of low toxicity, but its metabolic products are toxic, especially formaldehyde (methanal).

Methanol - Symbole leicht entzündlich, giftig und gesundheitsschädlich

Difference between methanol and ethanol

The chemical difference between the alcohol types ethanol and methanol is actually very small. Compared to methanol, ethanol only has a carbon chain that is one atom longer. Both alcohols are not toxic (in small quantities), but they have completely different rates of degradation after consumption. ADH (alcohol dehydrogenases) are involved in this process in the human body. While ethanol is first converted to acetaldehyde and then very quickly to acetic acid, methanol first produces the already highly toxic formaldehyde (methanal) and then formic acid. The latter is ten times stronger than acetic acid and can only be broken down very slowly, which is why this can lead to dangerous to life-threatening hyperacidity of the blood.

By-product of fermentation

Methanol is produced in minute quantities as a by-product of alcoholic fermentation through the enzymatic breakdown of pectins, which are mainly contained in the cell substances of berry skins and stems (i.e. not from sugars like ethanol). It belongs to the fusel alcohols, which are formed from fusel oils. Through intensive and long mash contact during mash fermentation or at higher fermentation temperatures, larger amounts are produced. This is why the proportion is usually much higher in red wines than in white wines. Especially the solid components of the grapevine such as leaves and stems (due to improper grape harvesting) as well as, to a lesser extent, the fruit pulp lead to increased methanol formation.

Spirits

The methanol content is also higher in the production of spirits. This is especially the case in the production of vodka because potatoes contain high amounts of pectin. Therefore, the methanol fraction is separated during distillation. This is relatively easy to do because methanol, at 65 °Celsius, has an even lower boiling point than ethanol (the drinking alcohol), at 78 °Celsius. If this separation is not carried out carefully, the distillate would contain dangerous quantities. In the past, the separation was omitted for products of questionable producers, such as in the times of the American Prohibition (1920-1933), because it was much easier and larger quantities of cheap hooch could be produced and sold. But even today, such illegally produced products still come into circulation from time to time.

Toxic property

Even the smallest amounts of 0.1 g of methanol per kg of body weight are dangerous to health, and life-threatening from 5 times that amount. From that point on, cramps, vomiting, breathing difficulties, blindness and, in extreme cases, death occur. Natural levels are between 17 and 100 mg/l in white wine and about twice as high between 60 and 230 mg/l in red wine. These amounts are harmless to health. Incidentally, the high methanol levels previously attributed to the Austrian speciality Uhudler have long since turned out to be false. Within the EU, there are limits defined by wine law: 200 g/hl for brandy, 30 mg/l for ethanol, 1,000 g/hl for fruit brandy and 200 g/hl for wine brandy (see under ADI).

An interesting piece of information comes from the website Chemie im Alltag (Oliver Reiser): Since methanol is oxidised by alcohol dehydrogenase much more slowly than ethanol, the best antidote for methanol poisoning is to keep the patient below an alcohol concentration of 1 per mille for several days. Ethanol acts as a competitive inhibitor for methanol, which means that ethanol binds preferentially to ADH (about 8,000 times better), so that the oxidation of methanol to formaldehyde and finally to formic acid, which is dangerous for the body, is prevented. Methanol is then excreted unchanged in the urine over several days as a water-soluble substance. See all wine ingredients under total extract.

Images: From UNECE web site,Public domain, Link

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