SULPHUR DIOXIDE AND SULPHITES ARE THEY REALLY NECESSARY?

Introduction

In the past years wine and sulphites are a hot topic, in particular since Italian Legislative Decree 114/2006, modifying Legislative Decree 109/92, implemented the Directive 2003/89/CE, the Directive on allergens that come into force on November 25th, 2003. According to this Directive, Food producers must show in the label all allergen (and toxic) items, between them also sulphur dioxide and its compounds (chemical formula SO_x – international code: E220-E221-E222-E223-E224-E226-E227-E228). Italian law prescribes that labels must show when sulphites are in bigger amount than 10 mg/l or 10 mg/kg of drinker’s weight.

Many studies have been held on sulphites toxicity, but results are not much clear nor easy to know. Therefore, we would like to clarify the main points about it. This article simply reports the unsystematic knowledge about sulphites, according to which a decision will be taken on their use or their prohibition.

What is sulphur dioxide?

Sulphur dioxide (SO₂) is a colourless gas with strong smell. Sulphur dioxide and its compounds are used, despite their high toxicity, as additives in all food productions, in particular wine-making. We can find it, e.g.,  in codfish, shrimps and conserves, fresh or frozen crustacean, dried fruits, conserves in oil or vinegar, jam and marmalade, vinegar, wines, drinks with fruit juices, dried mushrooms, processed grapes after vintage, flours and potato flour, processed salads (with spray, to preserve their fresh look…

Effects on wine

1)     Antiseptic effect: the main two antiseptic effects of sulphur dioxide are the selection on must microflora and the antimicrobial action for wines preservation.

2)     Antioxidant effect:  sulphur dioxide compounds catalizators with dissolved oxygen: this reaction protects wine from chemical oxidations as e.g. some polyphenols or some aromatic essences oxidation.

3)     Antioxidasic effect: sulphur dioxide inhibits the action of oxidase enzymes in the must and sometimes totally destroys them. Must is therefore protected from prefermentative oxidations.

4)     Solubilisation: sulphur dioxide, coming in contact with grape skins, helps along the diffusion of less polymerized colouring substances from the cells through little holes on the cell walls. In so doing, it also helps the anthocyans outflow.

5)     Mixer: a wise use of SO₂ improves wine fragrance and taste, because this preservative combines with some substances with unpleasant smell or taste, as acetaldehyde or pyruvic acid, that are no longer perceivable on taste.

6)     Clarifier: SO₂ finally has a bland clarifying action, because it helps along coagulation of colloidal substances and increases the spontaneous fall of the wine bottoms.

Current law fixes the maximum amount of sulphur dioxide for Italy in 160 mg/l for red wines, 210 for white wines and 400 for the sweet wines. The code for organic farming fixes instead a threshold of 60 mg/l for red wines, 80 for white wines and 120 for the sweet wines.

Fermenting yeast also naturally produces a little amount of SO₂, generally less than 10 mg/l and only rarely more than 30 mg/l.

Effects on human health

Sulphur dioxide is toxic if inhaled, corrosive and blistering for the respiratory system and could cause alterations in the B1 vitamin and of some amino acids metabolism. In particular, the main bad effect of sulphur dioxide in people with no hypersensibility to it, is the degradative action on B1 vitamin (Tiamin), which can cause important alterations on the sugar metabolism of human beings (diabetes).

Since 1973 allergic reactions have been related to sulphites, even if absorbed in very low dosage (about 1 mg), mainly in asthmatic subjects. (Ribereau-Gayon)

“People with sulphite allergy can experience asthma, respiratory distress, shortness of breath, labored breathing and cough. These individuals must reduce the assumption of sulphites, because consequences of excessive ingestion could be particularly severe, in some cases also lethal. Therefore, control organisations (in particular the American FDA – Food and Drugs Administration) established that for food (including wine) an amount of sulphites higher than 10 mg/l or kg must be indicated in the label. (Antonio Posocco).

WHO (World Health Organisation) fixed the daily admissible dose of SO₂ on 0.7 mg per day per kg of weight.

The admissible amount for a man is therefore between 42 and 56 mg per day, according to an average weight between 60 and 80 kg. If we daily drink half a bottle of wine (375 ml), we could easily absorb a higher amount of SO₂. Considering the maximum total amount of SO₂ consented by EU laws, i.e. 160 mg/l for red wines and 210 mg/l for white wines, SO₂ amount absorbed with half a bottle of wine is 60 mg for red wines and 79 mg for white wines. (Ribereau-Gayon) If we drink half a bottle of some special wines, such as those made with dried grapes or processed with Botrytis (which could contain up to 400 mg/l sulphites), the sulphur dioxide we absorb is so much as 150 mg (which is 2.5 mg/kg for one person weighting 60 kg and 1.87 mg/kb for a person weighting 80 kg).

“Conversion of sulphites into sulphates happens during their passage through the digestive system. In the stomach, where pH (acidity) is very low during the digestion, oxidation happens very slowly. On the contrary, it is much faster in the bowels or in the blood, where the the pH is subalcaline. Irritation of the stomach is caused by the sulphites that, having a strong acid reaction, release sulphur dioxide. The latter is the cause for pain and throwing up, if the absorbed amount is more than 3.5 mg per kg of weight (severe poisoning). Transformation of sulphites into sulphates is due to the intermediation of a hemoprotein (sulphites oxidase) containing molybdenum, that is abundantly found in the liver and in the kidneys. The well-known hangover headache, that we could feel after absorbing a high amount of sulphur dioxide, could be related to this hemoprotein action, that uses (even if in very little amount) oxygen in order to form sulphates. Our brain reacts with this kind of pain to this - even light - lack of oxygen.” (Antonio Posocco).

Something to think about

Even if wine is a complex food product (farming, wine-making, bottling) and is processed with many chemical substances, until today law concerning wine has been little restrictive: the ingredients listing in the label was not compulsory, as it was for other food items. Law, that recently imposed the printing “CONTAINING SULPHITES” or similar in the label, in fact does not help the consumer in choosing wines with low amount of sulphur dioxide, because this printing is compulsory for wines containing 11 mg/ l of SO₂, as well as for those containing 210 mg/ l. Furthermore, sulphur dioxide is the only wine preservative or additive whose toxic effects have been studied. That is why implementing methods avoiding the use of sulphur dioxide in wine-making is so important.

Many wine-makers have already reduced or banned sulphur dioxide in wine-making. This is only possible when grapes are healthy, and in particular thanks to extraction or use of natural antioxidants as e.g. oak tannins, ellegic tannins from grape skins, proanthocyanidins from grape seeds and ascorbic acid (Vitamin C).

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