Posted On 09 July 2020

The history of sulfur dioxide.

Sulfur dioxide (So2) or loosely referred to as Sulfites has been used by humans for thousands of years for its fumigation properties. The ancient Greeks knew its antiseptic qualities and used it in their everyday lives. The Greeks observed that it could kill all sorts of vermin (mice, cockroaches…) and help them keep ships, basements and storage rooms clean from them. In other ancient civilizations like Assyria and China, sulfite was also used as a fumigation agent to “clean” houses from bad spirits. Mentions of Sulfite use can also be found in Egypt and the Roman Empire.

The use of So2 to preserve wine seems to have started by the Romans. The Dutch and English merchants used it also excessively in the early 15th century in the same way. Before a wine was transferred into a barrel, a match dipped in sulfite would be burned. This not only killed any unwanted bacteria but also created a safe oxygen free atmosphere for the wine. In Germany during that time sulfite was banned on the grounds that “it abused man’s nature and afflicted the drinker”. It was only allowed again in 1487 when a royal German decree was published specifying how and how much So2 should be used. This was also the first ever official written proof of its use in relation to wine.

So2 helped wines in the 17th century to take on a more modern expression. During that time sulfite was not only burned in barrels but it was also used during the wine making progress. In the first English report for So2 use Dr Beale (Evelyn, 1664) recommended a small dose of So2 in grape juice to kill or suppress wild yeast and bacteria. This allowed the added yeast (So2 resistant) to start and finish the fermentation.

Pure Sulfite
Pure Sulfite

What exactly is So2 and why do we use it in wine and food?

Sulfur dioxide is the oxidised form of Sulfite which means it is made out of 2 atoms of oxygen and 1 atom of sulfite. It occurs naturally but can also be produced in a laboratory fairly easy since the only thing you need to do is burn pure sulfite. Without realising, wine merchants in the past produced So2 every time they burned it in barrels.

Sulfite is found everywhere on earth in rocks, minerals and even water. It is a fundamental element of life, found in every cell of every living organism. In wine so2 is also produced naturally by yeast during fermentation at levels usually around 10 mg/L and with some yeast strains even 30-40 mg/L. 

In reality, the majority of So2 found in wine is added during the various stages of production. We use it during the crushing of grapes, pressing of grape skins, maturation and bottling. Winemakers use it for its excellent antiseptic and antioxidant properties. Antiseptic means it protects wine and other foods from bacteria and undesirable yeast growth. Antioxidant means it protects our wine from oxidation by “capturing” oxygen. The lag of oxygen prevents bacteria and other microorganisms to grow. Delicate aromas found in wine are protected and preserved while browning due to oxidation is avoided. These properties make it very useful for the protection of other foods also. So2 is used widely in candy, prepared soups, soda, processed meat, potato chips, dried fruit, pickled vegetables, sausages and even fresh salads at buffets.

So2 if used with caution will help a winemaker avoid a lot of problems but if used incorrectly it can destroy a wine. When excessive So2 is used in wine it starts smelling like burned match sticks, that smell dominates the aroma profile and can cause irritation of the nose.

Wine-in-glass-fikardos-winery

Is So2 harmful for me?

Only people sensitive to So2 might have an allergic reaction. This rarely happens since the amount of So2 usually found in wine is very low to induce it. In Europe for example So2 is limited for dry white wines at 200 mg/L while for dry red wines at 150 mg/l. The highest amount allowed is 300 mg/L in some sweet wines. Even at this level it is definitely much lower than what you would find in dry fruit (1000-3000 mg/l). According to Hötzel et al., 1969 consuming 400 mg/l of SO2 (free and bound) every day for several weeks does not cause any effects.

Most wines in Europe have way lover levels of So2 than the limits mentioned above. The amount of So2 we use in wine mostly depends on the alcohol level, pH, acidity and polyphenols. Wines high in acidity and alcohol with low pH require very little So2. Wines low in alcohol with high pH levels are almost impossible to protect from bacterial spoilage.

3 Myths surrounding So2

Red wine has more So2 than white and rose.

Red wines actually require less So2. The tannins (polyphenols) found in red wines act as natural antioxidants and preservatives. Tannins are extracted from the skins, seeds, stems and oak barrels (if used). The more tannins we have the less So2 we need. White and rose wines are more vulnerable since they have no (or very little) tannins.

So2 gives me headache.

As mentioned above the amount of sulfite found in wine is barely enough to cause any problems. Only 1% of the population is actually sensitive to it. In addition, this headache claim is usually attached with red wines. It’s not the first time we hear someone claim that the red wine he/she had last night caused them a headache. Since red wines have the least So2 this can easily be dismissed. The main cause of headache comes from alcohol, tannins, histamine and tyramine. (Learn more on that from our previous blog post). 

Organic, biodynamic and natural wines do not have added So2.

Organic wines in Europe are allowed to have added So2 but in a much smaller dose. Of course, a winery can choose to join a private organic association that is more demanding. The same applies for biodynamic wines, for example Demeter a famous biodynamic certification label, allows up to 100 mg/l of total So2 in all wines. Natural wines are a bit more complicated, since there is no real definition for it. Some producers might choose to add zero so2 during the whole production process and some might add a bit. For example, members of the L’Association des VinsNaturels are advised not to use more than 30 mg/L for red wines and 40 mg/L for white wines. These numbers are extremely low compared to a normal wine but still are allowed. At the end of the day it’s another style of wine and if there are consumers that demand it then there is nothing wrong about it.

by Fikardos Fikardos, assistant winemaker.

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