Articolo disponibile anche in: Italian
The last few years have seen a rise in consumer interest in wines which are minimally altered and which limit a negative impact on health. Although the most interest is in organic wines, which have greatly improved in quality over the last 15 years, the market has brought attention to bio-dynamic, natural, vegan and, increasingly, wines with a low sulfite content.
Sulfites are molecules which, in wines, derive mainly from the use of sulfur dioxide, a preservative commonly used in all food sectors and added to wine in a gaseous form or, more frequently, as a salt (potassium metabisulfite). Their presence is evidenced by the label (“contains sulfites”). European regulations impose a limit of 150 milligrams per liter for reds and 200 milligrams for whites. These limits are lowered to 100 and 150 respectively in organic wines.
Sulfure dioxide is used in harvested grapes, in the juice and finally, in the finished product and provides a variety of effects on the wine. Most importantly 1. Anti-microbial (protects from bacterias and yeasts) and 2. Anti-oxidizing (limits oxygen entering in the wine).
However, there is a problem: sulfur is toxic and, according to the amount ingested, the consumer’s health is affected (headache the next day, for example). From this stems the desire of many producers to limit the use of sulfur, with the goal to eliminate it, where possible, without compromising the quality of a wine. This does not necessarily mean making a wine without any sulfites added. In the past, the vintner added an excessive dose of potassium metabisulfite. Today, he tries to ration its use.
Regarding the anti-microbial aspect, if we don’t want to use products that are more harmful or selective than solforosa (dimethyl-carbonate, lysozime) we can use filtration and maintain an immaculate cellar (not only the inside of wine containers and tubes, but the entire cellar is a potential breeding ground for microbes). As for the anti-oxidants, it is possible to use those which can substitute sulfur (tannins, gluthatione, abscorbic acid), but many producers use “natural” and practical means.
First of all, wine temperature should not be low during and filtration because, due to Boyle’s law of gases, a liquid absorbs a larger quantity of a gas at lower temperatures. Residual carbon dioxide from the fermentation of the alcohol is also used; a chemical-physical shield that impedes or limits the access of oxygen into the liquid. Lastly, in white wines we can take advantage of the anti-oxidizing effect of the dregs of fermentation, added to the solution with the “batonage” technique.
The use of inert gases like argon, carbon dioxide or nitrogen is frequent: they prevent the wine from entering into violent contact with the oxygen that saturates empty spaces (tanks, filters, tubes) where they could come into contact with air.
Lastly, a paradox of wines without sulfites added: the majority of these wines will nonetheless be labeled “contains sulfites”. This is because the majority of yeasts produce a quantity of more than 10 mg per liter (even as much as 40 mg per liter!) of sulfites during alcohol fermentation, a quantity above the allowed amount dictated by law: even without the addition of sulfur the wines will contain sulfites!