Sulphites (SO2) in Wine: Top 7 Facts
But two words strike the imagination and create more controversy than any other:
are now seen on almost every bottle of wine today.
Then, what are sulphites really? Where do they come from? Are they really bad for people’s health and responsible for causing headaches? What about Sulphur-free wines, any good?
Let’s bust some myths and be, for once, factual about SO2.
What is Sulphur Dioxide aka SO2?
Sulfur or Sulphur is a chemical element (atomic number 16, for the geeks in the crowd) found everywhere on Earth, although there is even more of it on Venus that has clouds full of it.
More seriously, Sulphur is found in rocks and everywhere underground, and is also a fundamental element of life, found in every cell of every living organism.
If you’re wondering what Sulphur typically smells like, think of the odor around hot springs and volcanoes, or more common in our everyday lives the smell of cooked eggs or cauliflower.
As the name indicates, Sulphur Dioxide is the oxidized form of Sulphur, where 2 atoms of Oxygen are bound to 1 atom of Sulphur. SO2 is the result of the combustion of Sulphur, much like CO2 is formed when burning carbohydrates.
Sulphur Dioxide is therefore very much of a ‘natural’ product, in the sense that it is easily and commonly formed in nature, and rather easy to produce. No need for complex chemistry, high-tech factories or complicated reactions. Burning pure Sulphur is all it takes!
This simple way of producing SO2 is in fact commonly used in winemaking to sanitize wine barrels by burning a small piece of Sulphur inside the oak container (an operation called méchage in French, used in pretty much every winery that has barrels).
Why Sulphites in Wine?
Sulphur dioxide has two main properties that are interesting in winemaking:
SO2 is Anti-Oxydant:
This means that if oxygen is present around it, it will ‘capture’ it, or bind it, preventing it from oxidizing other molecules such as aromas. The binding of oxygen by SO2 also means that it not available for bacteria or other micro-organisms, not allowing them to ‘breathe’ and develop.
SO2 is an Antiseptic:
That means that germs don’t like it and are affected by it, they’re bothered by its presence and unable to develop well with it.
In winemaking, these properties are interesting for two reasons:
- The anti-oxydant effect of Sulphur dioxide prevents the natural aromas of the grapes and wine (the ones that give wine its fruity flavors) to get oxidized should some oxygen be in contact with them. To make a fruity wine, that smells of something like the grapes it was made from, SO2 helps a lot. This is particularly true for some grape varieties with strong natural varietal character such as Sauvignon Blanc.
- The Antiseptic effect of SO2 helps with inhibiting the development of ‘bad germs’ in the wine such as acetic bacteria or fungi that would make the wine smell and taste bad should they start growing in it. The natural fate of grape juice is to become wine, then vinegar. Sulphur dioxide allows winemakers to stop this natural process at the ‘wine’ status, preventing it from going any further down the rotting line.
Related Article: Infographic & Guide to Sauvignon Blanc Wine Grape Variety
Because SO2 is one of the most ‘natural’ molecules to have such beneficial properties, it is the preservative of choice to winemakers and the wine industry.
For the same reason, it is also commonly used abundantly everywhere in the food industry in many products such as candies, jams, fruit juices, ham and other cured meats, soups, French fries or dried fruits!
How much Sulphur Dioxide in wine?
The amount of SO2 that can be added to a wine and that it can contain is strictly regulated and controlled around the world.
Any wine containing more than 10 parts per million (ppm) of sulfur dioxide must bear the famous ‘contains sulfites’ mention somewhere on the label. This is why you see it on almost any label or back label.
As an example of how much SO2 is allowed in wine, one of the strictest regulations, the European one (Reg. CE No 606/2009) establishes the following limits:
- Dry Reds: 150 mg/L (150 ppm)
- Dry Whites and Rosés: 200 mg/L (200 ppm)
- Sweet reds (more than 5 g/L of sugars): 200 mg/L (200 ppm)
- Sweet Whites and Rosés (more than 5 g/L of sugars): 250 mg/L (250 ppm)
- Some specialty wines such as Botrytized (e.g. Sauternes): 300 mg/L (300 ppm)
Reds generally contain less SO2 because they already contain much more natural antioxidants and antiseptics: the tannins and other phenolics.
More Sulphur Dioxide is added to sweeter wines to protect them better against the bacteria and fungi that, like us, love sugar!
Sulfites in foods are added in various forms, each of which has a particular code in European Union’s regulation, although these do not apply yet to wine: E220 for sulfur dioxide, E221 for sodium sulfite, E222 for sodium bisulfite, E223 for sodium metabisulfite, E224 for potassium metabisulfite, E226 for calcium sulfite, E227 for calcium bisulfite and E228 for potassium bisulfite.
Is SO2 Responsible for red wine headaches?
Medical research has not yet certainly established the relationship between sulfites and headaches.
What is sure however, is that red wine contains less Sulphur Dioxide than white and rosé as the above regulations show. Generally speaking, the drier the wine, the lesser the amount of SO2 it contains.
So, if you’re sensitive to Sulphites and feel it increases your headaches, avoid very sweet wines, white and rosés in particular (we never advice to drink White Zinfandel, but particularly in that case!), and favor dry reds.
There are other compounds in wine such as histamines (involved in allergies), tannins, and of course alcohol itself, that are more likely connected to the unfortunate headache effect of our favorite beverage.
Are Sulphites Harmful to your Health?
Generally speaking, the answer is no.
The relatively small amounts of Sulphur dioxide contained in wine consumed with moderation are quite easily processed by most human bodies.
It can be a different story with the consumption of large amounts of sweet wines that contain a lot of SO2.
However, about 5-10% of people with asthma have a severe sensitivity to sulphites and develop strong allergies. Although this affects less than 1% of the population, this is the main reason why US authorities require the labelling of wines with sulfites above 10 parts per million (ppm).
Sulphites and pregnancy
The number 1 reason why pregnant women should avoid wine is alcohol (ethanol) and its negative effects on the development of the embryo not so much sulphites.
Can I Smell Sulfites in Wine?
Yes, you can!
Trained and/or sensitive tasters can smell sulfites in wine at around 50 ppm, depending on each individual wine obviously. The more flavorsome the wine, the more Sulphur Dioxide is needed for detection.
Important concentrations of SO2 can affect the smell of the wine. It is also most-often noted on the finish, with some wines displaying a strong flavor of Sulphur after you’ve tasted (or swallowed) on the back of the mouth.
Related article: example of a sweet wine with an annoying level of Sulphur Dioxide.
The warmer the wine, as in its temperature, the more obvious is SO2 to the smell and taste.
Decanting or letting a wine ‘breathe’ before tasting oxidizes the Sulphur Dioxide, and generally brings its impact on the experience to a lower level.
Challenges of Sulphite-Free Wines
Making wines without Sulphites involve taking many precautions to avoid oxygen getting in contact with the wine all along the winemaking process and affecting (or ruining) its aroma and taste.
Challenges and solution for making Sulphite-free wines include:
- Machine harvesting grapes and making decent Sulphur-free wine is nearly impossible as grapes and grape juice get oxidized very quickly in the harvester, before even reaching the winery. Mandatory manual harvest means Sulphur-free wines cannot be produced at a low price.
- Pressing is a critical phase in winemaking when the must or wine is particularly exposed to air and oxygen. It is generally a step in the winemaking process when SO2 is added. Special precautions must be taken, such as using inerting gas (nitrogen or CO2) around the press.
- Similarly, bottling often introduces much dissolved oxygen to the wine. Special bottling lines can be equipped with protective material.
- Obsessive hygiene at the winery must be applied to prevent any germs from entering in contact with a wine that has no SO2 protection. Acetic bacteria (giving volatile acidity), Brettanomyces (producing funky- and sweaty-smelling volatile phenols), or fungi can easily develop in sulphite-free wines if not enough precautions are taken.
- Fermentation or maturation in wine barrels is riskier and has to be shorter because the wood lets some oxygen get into the wine through the staves. Sulphur-free wines are more often made in clean, full and closed stainless still tanks.
- But new techniques, and new natural products such as antioxidant tannins are being developed, tested and entering the market, allowing more and more willing winemakers to achieve producing excellent wines without or with very little Sulphites. Made well, these result tasting more ‘natural’, or more like the natural taste of the grapes and of the natural fermentation process done by yeasts.
Hoping this was helpful, if it was let me know in the comments section below.