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Methanol

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

This monovalent alcohol (also known as carbinol, methyl alcohol, wood alcohol, wood spirit) is a colourless, burning tasting liquid with an unmistakable sweetish smell. Although it differs considerably from ethanol (drinking alcohol), it is hardly possible to recognise its taste by overlaying it with other aromatic substances in alcoholic drinks. Even the ancient Egyptians produced methanol by pyrolysis (splitting of organic compounds by high temperatures from 200 °C) of wood and embalmed their dead with a mixture of substances. In 1834, the French chemists Jean-Baptiste Dumas and Eugène-Melchior Péligot gave it the name "methylene". 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

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

The chemical difference between the alcohol types ethanol and methanol is actually very small. Simply put, ethanol has a carbon chain that is only one atom longer than methanol. Both alcohols are not toxic (in small amounts), 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 is first converted to formaldehyde (methanal), which is already highly toxic, and then to 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 a dangerous to life-threatening acidosis of the blood.

Methanol is produced in very small quantities as a by-product of alcoholic fermentation by enzymatic degradation of the pectins which are mainly contained in the cell substances of the berry skins and stalks (i.e. not from sugars like ethanol). It belongs to the group of fusel alcohols which are formed from fusel oils. Large quantities are produced by intensive and long mash contact during mash fermentation or at higher fermentation temperatures. That is why the proportion is usually much higher for red wines (with berry contact) than for white wines (without). 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 flesh lead to increased methanol formation.

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 has an even lower boiling point at 65 °Celsius 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, separation was omitted for products from questionable producers, such as in the days of American prohibition (1920-1933), because it was much easier and larger quantities of cheap fuselage could be produced and sold. But even today, such illegally produced products still come into circulation from time to time.

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

Pictures: From UNECE website, Public domain, Link

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