Wine and chemistry are among the most debated subjects of the world of wine. In particular by consumers who, legitimately, are concerned about the genuineness of what they pour in their glasses. Sometimes we forget wine is, in any case, the result of a complex chemical process in which the many elements making it undergo radical changes, however essential for the making of the beverage of Bacchus. In other words, Nature makes use of chemistry to transform grape juice into wine. Frequently, this is undeniable, man does the same to control certain processes and to shape the wine in order to give it specific qualities and characteristics. We should remember the natural process of vinification is to transform grape juice into vinegar: man makes use of technology and chemistry in order to avoid this unhappy end.

 The need of controlling the vinification process does not however justify the abuse of chemistry and technology. The limit is not always defined by the good sense of the one making use of it, but also by the respect for those who want to drink wine with awareness without side effects for their health. Last but not the least, respect for vine, grape, wine and the millenary culture and tradition they represent. Making a wine with the least number of faults is of course desirable and a fault, no matter it is “natural” or not, is however a fault lowering the quality of wine. On this regard it should be remembered, in order to reach this goal, it is however and always indispensable the quality of the raw matter: grape. If it is true from a quality grape it can be produced a great quality wine, from bad quality grapes it can be obtained - in the best case and thanks to the skill of the wine maker - a mediocre wine. The difference between a good wine maker and a less good one, it is not what he or she can make in the winery, indeed what he or she can obtain from the vineyard, alone or with the fundamental help of the agronomist.

 Among the many helps used for the production of wine, the most used one certainly is sulfur dioxide. Not only the chemical element mainly used in enology, but also the most debated one. Using the least possible quantity of sulfur dioxide in wine certainly is wished - and when this happens, the result can be greatly appreciated in the glass - and it should be said that completely eliminating its use in enology is virtually impossible. Nature, with its goodness, adds sulfur dioxide to wine during fermentation, as this simply is a byproduct of the activity of yeast. Of course it is a lower quantity than what man - by law or by need - adds to the must or to the wine during production. In other words, a wine without sulfur dioxide - or simply, with no sulfites - cannot exists. It can of course be limited its use, but it is not however possible to completely eliminate it from wine.

 Sulfur dioxide, no matter how it is being used, allows wine makers to stabilize the wine, to avoid the development of certain faults, including oxidation. It should also be noticed sulfur dioxide is widely used in food industry, sometimes used in a higher quantity than what is permitted by law in wine. According to European laws currently in force, the maximum quantity of sulfur dioxide which can be used for the production of wine is 150mg/l for red wines and 200 mg/l for white and rose wines. The maximum quantity permitted in sweet wines is quite higher, currently set to 400mg/l. It should be noticed these represent the maximum permitted quantity: in most of the cases the quantity of sulfur dioxide found in wines is lower. Finally, it must be said sulfur dioxide is not however healthy for man and, in certain cases, it can cause important allergies in subjects particularly sensitive to this gas.

Crystals of potassium metabisulfite: the most common way to add sulfur dioxide to wine and must

 On this regard, it should be noticed the World Health Organization (WHO) has recommended a maximum daily intake of sulfur dioxide of 0.7mg per kilogram of body weight. A quick calculation and considering a male subject with a 80 kilogram of weight, the maximum daily intake equals to 56 milligrams. This means that, in case in a white wine has been used the maximum quantity set by law, half a bottle of wine - 375 milliliters - is enough to exceed the maximum daily intake. Wine and, not to forget, drinks and foods containing low quantity of sulfur dioxide are healthier and should however be preferred. Talking about limits, an intake of 1.5 grams of sulfur dioxide for kilogram of body weight is considered by World Health Organization as lethal. In particularly sensitive subjects, sulfur dioxide can cause migraine as well as disorders and allergic reactions.

 Sulfur dioxide easily bounds with oxygen and this is one of the reason why it is being used in enology, therefore avoiding the oxidation of wine. In case the quantity of sulfur dioxide can be of concern for the health, therefore wishing to get the least possible quantity, its predilection for oxygen can certainly be useful. In fact, by oxygenating the wine before consumption, the quantity of sulfur dioxide can considerably be lowered. The quickest and most effective way is to swirling the glass - by allowing the wine to wet the broader possible surface - an operation which can also free 30-40% of sulfur dioxide contained in a wine, as well as favoring a better development of aromas. The same result can be obtained by decanting a wine - a “traumatic” operation to be done only in case a sediment is present - whereas it is completely useless uncorking a bottle some hours before consumption.

 The reasons why sulfur dioxide is used in enology are many. It has an antiseptic effect, therefore added to the must it works a selection of bacteria and yeast by eliminating the least resistant ones while ensuring, at the same time, a better stability. The antiseptic action of sulfur dioxide therefore works a selective action on yeast which will ferment the must, while remembering that - in general terms - bacteria are less resistant to this gas than yeast. Sulfur dioxide is useful during the decanting of the must, as it can delay the activity of yeast, therefore preventing the start of fermentation while favoring the decanting of solid parts. It favors a better extraction of coloring substances in red grapes thanks to its property of making the skins more permeable. Finally, as already said, it has a very good antioxidant effect thanks to its property of easily bound with oxygen, therefore avoiding its bond with the substances of must and wine.

 Sulfur dioxide can be added to the wine and must in different ways. The most traditional and old method - as well as the least controllable one in terms of quantity actually added - consists in burning a tablet of sulfur inside the container which will be used for wine or must. The burning of sulfur produces, in fact, sulfur dioxide. Modern enology, in order to rigorously control the quantity of added gas, makes use of other methods, of which the most common one consists in using potassium metabisulfite. This substance, having the aspect of white salt, when it gets in contact with the must or wine produces sulfur dioxide in a quantity of about 0.55 grams per each added gram. Other methods of adding sulfur dioxide make use of liquid solutions or cylinders containing this gas that, it should be noticed, is colorless however easily recognizable for its characteristic pungent smell.

 For the sake of a better information, it should be said in recent times they are trying to find alternatives to the use of sulfur dioxide in enology, not only by limiting quantity, but also by completely avoiding its use. Some of these alternative attempts have produced very promising results that make us think of a wine making future without adding sulfur dioxide, while remembering - in any case - this gas is however produced during vinification. Wines produced with these techniques are now available in the market, usually emphasizing in the label they are wines with no sulfites: indeed it would be more correct saying they are wines “with no added sulfites”. The quantity of sulfur dioxide produced during vinification is however lower than every possible adding done for wine making purposes and the production of a wine with no added sulfites certainly is wished, last but not the least, for the lower effects on health.

 According to an organoleptic point of view, sulfur dioxide can drastically change every sensorial aspect of wine. Some effects certainly are positive, whereas others are completely negative, effects which generally happens with its bad use, in particular with the excess. In case it is properly used - and this does not mean using it at the maximum quantity set by law, and however using a far lower quantity - it gives the wine a better stability over time. Recognizing sulfur dioxide in wines is very simple, in particular to the nose: when used in excess or improperly, it will always be perceived the unpleasant and typical smell of sulfur which tends to cover everything else. Excessive quantity of sulfur dioxide also produces an accumulation of acetaldehyde that, when ingested, causes disorders for the health and it is also more toxic than ethyl alcohol. Moreover, the excess of sulfur dioxide causes the formation of hydrogen sulfide and mercaptans, giving the wine an unpleasing aroma of garlic and rotten eggs.

 The preservative effect of sulfur dioxide ensures the wine a longer life, in particular for its antioxidant effect, therefore preventing the alteration of aromas and of taste with typical oxidized characters. Talking about wine's appearance, sulfur dioxide stabilizes color, in particular in red wines, therefore favoring the extraction from the skin during maceration and fermentation. The aroma of wines properly treated with sulfur dioxide is generally “finer” thanks to its selective effect on yeast and bacteria, therefore allowing a more regular and controllable fermentation. The correct use of sulfur dioxide also reduces the quantity of volatile acidity - which can be perceived with a more or less intense aroma of vinegar - thanks to its antiseptic action against acetic bacteria. Antiseptic and antioxidant effects, in case this gas is properly used, allow a longer keeping of the original aromas of wine. Finally, during its volatilization, sulfur dioxide helps the perception of certain fruit aromas.

 The excess of sulfur dioxide - according to the sensitivity for this gas, in some subjects already perceivable in a quantity of 20-30mg/l - gives the wine a sulfurous flavor, hiding the aromatic and gustatory qualities of wine. The correct use of sulfur dioxide improves the taste of wine, not because of its organoleptic characteristics, indeed for its preservative effect, preventing oxidation and the development of bacteria. Finally, it should be noticed European laws requires the indication in label of the mention “contains sulfites” in all the wines in which the content of sulfur dioxide is higher than 10mg/l. This mention is virtually found in every wine, also in those produced with no added sulfur dioxide, as yeast, during fermentation and according to the type, can produce a variable quantity of this gas from 6 to 40 mg/l. In this sense - and unjustly - law makes no distinction between a wine produced with no added sulfur dioxide and one containing the maximum quantity permitted by law, that is 200mg/l for white and rose wines, 150mg/l for reds.