Sulfur Dioxide: FRIEND or FOE?

Wine lovers, do not fear sulfur dioxide – it is a friend and our defender!  I know that might strange coming from me, as I am a cheerleader for low intervention winemaking and a BIG fan of the natural wine movement.  HOWEVER, I feel there is a strong need for someone to stick up for sulfur dioxide and debunk the myth that SO2 is our enemy.  Most consumers have a misconception that Sulfur Dioxide is responsible for every unpleasant side effect that they experience after consuming wine.  As a result, many wine drinkers then assume they have a sulfur allergy, but sulfites very rarely are the true culprit and oftentimes play the scapegoat to alcohol and histamines.  Rather, wine drinkers around the world should THANK THEIR LUCKY STARS and rejoice in the glory of SO2 because without it, wine as we know it today would be near impossible.

Sulfur dioxide is an important antioxidant and antiseptic.  It is used in small doses to combat oxygen; O2 is both good and bad for wine.  In small doses, oxygen can have positive effects on some wines; in fact, oxygen is an invaluable aid to the fermentation process as yeast rely on oxygen to jump start the process.  Over time, however, wine that is exposed to oxygen will break down and eventually turn into acetic acid (aka vinegar).  That is a natural process and it is unavoidable.  Sulfur dioxide fights the battle against oxygen by readily combining with O2 to form sulfuric acid, changing its molecular structure and thus rendering it inactive.  Sulfur dioxide also inhibits the activity of micro-organisms and guards wine against bacterial spoilage.

The occurrence of a completely sulfur free wine is extremely rare as sulfur dioxide is produced in minute quantities by yeast as a byproduct of fermentation.  A winemaker’s decision to add SO2 before and after fermentation is primarily a means to block the negative action of O2 and bacteria.  Therefore, all styles of wine benefit from small amounts of sulfur dioxide.  Red wines require smaller doses of SO2 because they have the benefit of natural antioxidants.  Grape skins are a reservoir of various phenolic compounds; one such type, flavonoids/polyphenols, are powerful antioxidants (not only for the wine but for the individual consuming the wine).  Tannins are a specific polyphenol that create a dry, bitter, sometimes astringent feeling on the tongue, and also add body to wine and help create a sense of weight on the palate.  Grape varieties with thick skins have more tannins and offer better protection against oxygen, and therefore need lower doses of added sulfur dioxide.  Moreover, too much added SO2 in red wine can have a negative effect as sulfur dioxide binds to polyphenols creating hydrogen sulfide (H2S): this is known as reduction.  Reductive taint in a wine will have a foul smell of rotten eggs.

The vast majority of white wines are crafted with little to no skin contact because most consumers prefer a light and crisp style of white wine.  Winemakers are reliant on anaerobic winemaking strategies and the use of sulfur dioxide to protect their white wines from oxidation and bacterial spoilage.  Sweet white wines require even higher levels of sulfur dioxide because sugar readily binds to free SO2 and renders it inactive.  SO, if you gleefully enjoy glasses of Spatlese Riesling with no ill effects to your body (besides a hangover), you can rest assured, sulfur is your friend!

I felt compelled to write this because most customers are confused by what is happening to their bodies after they consume alcohol and are quick to point a finger at “sulfur” and disregard the other factors at play.  Most people experience uncomfortable side effects after consuming red wine.  This is typically in connection with higher alcohol levels found in red wine (sometimes as high as 16-17% abv!) and the fact that most people are often dehydrated when they are consuming alcoholic beverages.  Your hydration level, what you ate that day, and exposure to extreme heat, can accelerate the ill effects of alcohol.  Some people also experience intolerances to histamines and other phenolic compounds that are found in red wine – which is something to consider and explore further.

Since a very very small percentage of the population actually suffers from a sulfur allergy, it is important to listen to your body when you drink wine AND if you are experiencing some uncomfortable side effects, it might be worth consulting your doctor first.  Second, keep a journal and take notes on how you feel after drinking specific wines.  Do not forget to take note of what else you had to drink and eat that day and make sure to take care of yourself and your body when you consume alcoholic beverages.  Third, experiment with naturally made wines where the winemaker is using organic, biodynamic or sustainable vineyard practices and continuing this mentality in the cellar with low intervention and minimal additives.  You can also play around with low sulfur wines and buy wines that have “no added sulfur” as a means to figure out what makes your body happiest.

Disclaimer: I am not a doctor by any means, this write up is merely a helpful pondering with thoughtful suggestions based on an accumulation of wine encyclopedias, WSET study guides, and wine production textbooks (specifically the Oxford Companion to Wine 4th Edition by Jancis Robinson, David Bird’s Understanding Wine Technology, and WSET Level 4 Diploma Unit 2 Wine Production Study Guide manual) that I have read in conjunction with personal experience from my work in the wine industry and in wine production. If you have any further questions or comments on this topic, feel free to email me directly at

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