History of wine – Composition of wine and must (2)

History of wine - Composition of wine and must (2)


Among the harmful consequences of drinking wine is alcoholism, caused by the ethanol content. (The fermentation process also has a harmful consequence.)

Ethanol Molecule

Yeasts that overcome bacteria in wort (the fermented liquid) grow, consuming fermentable sugars (sugars that can ferment into ethyl alcohol). The alcohol concentration, measured as a percentage of the final volume of the wine, is usually between 7% and 14% in table wines, between 11% and 13% in sparkling wines, between 16% and 18% in Jerez and other generous wines, and below 17% in ports and dessert wines.

The boiling point is one of the easiest methods for detecting the presence of alcohol in wine.

There are also small amounts of other alcohols in wine, such as methyl alcohol (CH3OH), produced by enzymatic action on pectins in grape skin and not by fermentation. Despite the presence of methyl alcohol in must, the proportion of methyl alcohol in white wines is lower than in red wines because pectin is concentrated in the skin and not in the must.

Methyl alcohol

The must is cooled before fermentation to remove the methyl alcohol to concentrations below 30 ppm.

Studies on the presence of methanol in wines around the world have recorded concentrations of 60 mg/liter (40-120 mg/liter) in white wines and 150 mg/liter (120-250 mg/liter) in red wines. Although methanol is toxic, the quantities present in wine are not entirely malignant, since lethal doses of 340 ml/kg of body weight would require an average person weighing 70 kg to drink approximately two hundred liters.

When the famous tears from the glasses slide down, it indicates that the glycerol content in wines is high. In addition to polyols, one of the most significant trialcohols is glycerol (glycerin), whose concentration is related to the fermentation temperature, the overall alcoholic strength (the higher the alcohol content, the higher the alcohol content, the higher the amount of glycerol) and the color of the wine (higher in red wine varieties than in white wine varieties).

Glycerol molecule

The concentration of this alcohol is higher in table wines. It is common for glycerol levels to vary between 15 and 25 grams per liter in wines. Botrytis cinerea, a common fungus, produces glycerin as a by-product of its growth. Red wines tend to have higher amounts of glycerol due to high fermentation temperatures.

Because of its sweet taste and filling sensation in the mouth, glycerol is believed to be 70% glucose (see the previous sentence). When a certain type of tear is left on the inside walls of the glass after pouring water into it, glycerol is easily detected.

Erythritol is one of the polyols present in wine, and its concentration is affected by the yeast strain that ferments the wine, for example Saccharomyces cerevisiae has less effect on erythritol concentrations than Kloeckera apiculata (this yeast dies in the early stages of fermentation if exposed to higher alcohol concentrations).

Erythritol molecule

Arabitol, sorbitol (an isomer of mannitol with six hydroxyl groups), inositol (a fruit polyol with six hydroxyl groups) and mannitol (a compound with six hydroxyl groups commonly found in foods). These polyols give the wine its sweetness, and their concentrations increase when the noble rot of the grape is present.

Arabitol molecule
Sorbitol molecule
Inositol molecule
Mannitol molecule

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