What are sulfites (SO2) and why are they an important part of winemaking? Sulfites are inorganic salts that can act as preservatives and antioxidants in many types of food and drinks. Sulfites like sulfur dioxide, sodium bisulfites, and meta-bisulfites help reduce browning on fruits and vegetables and stabilize the potency of medications. But when it comes to winemaking, they help prevent the growth of unwanted yeast and bacteria in wine.
According to usualwines.com, SO2 naturally occurs in wine as a byproduct of the fermentation process. Because of this, there are ways of making sure the levels of the SO2 in the wine aren’t harmful to the person enjoying the wine.
Testing Methods
Winemakers have a couple different options when it comes to testing the levels of SO2 in the wine before it hits the bottle. The two main ways are The Ripper Method and the Air Aspiration/Oxidation Method.
When it comes to the Ripper Method, Ethan Baker, Cellar Master for Aurora Cellars, explains that “it relies on the reaction of sulfur dioxide in the wine with iodine that is being titrated into the solution.” While the Ripper Method is a much faster and cheaper method, winemaking teams can run into difficulties as well as other interferences with different compounds in the wine. Because iodine likes to bind to other chemical compounds in the wine – such as sugars, phenols, and aldehydes – this can result in an answer that is skewed and can throw off results.
At Aurora, our team does what is called the Air Aspiration/Oxidation Method. With this method, the SO2 is being separated from the wine to get a clean sample without interference from the other potential compounds, explains Baker. During this process, acid is added to the wine, which is then subjected to a positive pressure that separates molecular SO2 from the liquid. The gaseous SO2 passes through tubing to a second receptacle where it is then trapped by a hydrogen peroxide solution, forming sulfuric acid.
After a certain amount of time, the amount of sulfuric acid that is in the peroxide trap is determined by the titration – or the technique where a solution of known concentration is used to determine the concentration of an unknown solution – with sodium hydroxide (NaOH).
For example, if your NaOH solution starts at 5 mL and you titrate the sample back to green and the tube shows 6.5 mL, you multiply the difference of 1.5 by 16 and you get the level of free SO2 to be 24 mL.
Sulfite Sensitivity
There have been studies done when it comes to sulfites in wine and allergies. According to Dry Farm Wines, sulfites are often the blame for hangovers. However, they haven’t been shown to trigger headaches or health issues in 99% of people – which means only about 1% of the population is sensitive to sulfites. If you happen to be in that 1%, some side effects you may run into when consuming sulfites include headaches, digestive issues, rashes and even heart issues.
A lot of common foods have sulfites in them and you may not even know it. If you do have a sulfite sensitivity, you may react to a variety of foods, including:
- Dried fruit
- Pickled food
- Jams and jellies
- Potato chips
- French fries
- Shrimp
- Scallops
- Parmesan cheese
- Mushrooms
Generally, sulfites are safe but if you’re experiencing some sort of reaction to wine, it may be something else, including high alcohol content, high residual sugar content, histamines, or possibly a combination of unlabeled wine additives. But if sulfites are harmless, why does wine need to have “CONTAINS SULFITES” on its label?
Sulfites in Wine
From a health perspective, sulfites matter to some people. From a winemaker’s perspective, they are incredibly important.
For thousands of years, sulfur dioxide has been used in winemaking. Romans discovered it would keep their wine from turning into vinegar. Nowadays, it is used to preserve the flavor and freshness of the wine.
When visiting a tasting room or purchasing wine anywhere in the country, you will most likely see the words “CONTAINS SULFITES” on the label. This is because, by law, wines that contain more than 10 ppm (parts per million) sulfite must display it on the label. But what does this mean for the wine?
During the fermentation process, sulfite levels naturally range from 10-20 parts per million. Baker explains that “most, if not all, that SO2 is immediately “consumed” – or bound – to another compound rendering it useless.”
“Our goal during fermentation is to have very little to no SO2 in the wine because if we add more SO2 than the wine is already naturally producing it will inhibit the fermentation process,” says Baker.
Once the fermentation process is complete, our cellar crew’s goal is not to let the SO2 levels dip down but to get them up. At this point, the SO2 is used as an antioxidant and antimicrobial in the wine.
Just like everything else, sulfite levels will vary from wine to wine. Researchers say white wine will generally contain more sulfites than red wines do. Because red wines get their color from the extracted grape skins during the fermentation process, they are gathering more tannins, polyphenols, and a variety of other antioxidants that keep the wine from spoiling. As a result, red wines typically don’t need as many added sulfites to stay fresh.
When drinking white wine, chances are the winemaker may have added extra sulfites to keep it from going bad as they ferment due to the juice having no skin contact during fermentation.
Sulfites in Common-Use Items
Sulfites are used to preserve many drinks and food. In some countries, adding sulfites to foods like fresh salad or fruit salads, or meats – like minced meat or sausage meat – is illegal. Adding sulfites to beer and wine is permitted in most countries.
The Australasian Society of Clinical Immunology and Allergy says some commercial foods that contain sulfites include dry potatoes, gravies, sauces, fruit toppings, maraschino cherries, pickled onions, Maple syrup, jams and jellies, biscuits, bread, pies, and pizza dough. When it comes to salads and seafood in restaurants, some may sprinkle sulfur powder on the food to keep it from discoloring.
