Sulfites in Wine, Explained


“Contains Sulfites”. What’s the deal? Most people have heard of sulfites in wine, but not many know what this actually means. This article will give you my point of view, a basic understanding of the term, and why sulfites are added to wine (or not).

First off, “sulfites” are commonly referred to as “SO2” or “sulfur dioxide”. SO2 is a chemical compound composed of sulfur and oxygen. It was first used by the Romans in winemaking, when they discovered that burning sulfur candles inside of winemaking vessels (while not in use) kept them fresh and free of vinegar smells.

The basic principle is that SO2 acts as an antioxidant (a safeguard against premature oxidation), as well as an antiseptic and anti-microbal agent. It basically keeps the wine fresh and free of spoilage organisms, although it doesn’t completely prevent these things. It also has a different effect on wine based on the wine’s pH level. The more acidic (lower pH) a wine is, the less SO2 is required to keep the wine fresh. When the wine is lower in acid and higher in pH, more SO2 is required to have the same effect. White wines tend to need higher levels of SO2 because they oxidize easily, while red wines require less as the tannins and other compounds that occur naturally on the skins of grapes act as an antioxidant and antiseptic. The graph below gives you a very basic explanation of the amount of SO2 commonly recommended for amateur winemakers based on the type of wine they are making.


SO2 is commonly added to wine in various stages of the vinification (winemaking) process, in the form of potassium metabisulfite powder or liquid. A dose is sometimes added when the grapes are initially crushed (usually when a lab-created yeast is going to be used for fermentation – to stun any unwanted, wild yeasts or bacteria on the grapes), when malolactic fermentation is complete (malolactic bacteria are very sensitive to SO2), when the wine is being racked (transferred from one vessel to another, to prevent oxidation and spoilage organism growth), while it’s aging in a barrel (to maintain “proper” levels, since over time the “free” SO2 becomes “bound” and ineffective), and when it’s bottled (to prevent oxidation and microbal growth during the transfer to bottle). Not all winemakers add SO2 at all of these stages, and some don’t add any at all. The amount and frequency of SO2 additions is up to the winemaker and there is a lot of controversy regarding the “right” amount to add to a wine.

Some natural winemakers will avoid adding any SO2 at all to their wines, in the name of natural winemaking. These wines tend to oxidize more quickly and have a shorter shelf life (and although I’m sure someone out there disagrees, this is the general consensus). Wines with no SO2 added are also more prone to spoilage during shipping, and when temperatures rise above 60F (warmer temperatures are favorable to spoilage organisms).

Natural winemakers will argue that adding large doses of SO2 to wine strips it of its natural complexity and character. In fact, when you add a dose of SO2 to a light red or rosé wine, it temporarily bleaches some of the color out. As a new winemaker, I found this to be very alarming. It was even more interesting to see the color bounce back over the course of a few days. I agree, wines that are sans soufre can be more soulful and interesting. I prefer wines that are honest, real, and natural, but I also like wines that are clean and orderly. What I’ve noticed most often in the wines that I drink is that the winemakers add SO2 selectively and in low levels to keep the wine fresh and clean without tainting it with high levels of SO2. For example, a winemaker may add no SO2 at all to their wine until it’s being bottled, and then they will add a very low amount (say, 10-20ppm) to prevent oxidation and microbal growth during the transfer to bottle.

There is also controversy about allergies to SO2. There are people out there with severe allergies to this compound, usually in the form of an asthmatic reaction to high levels of SO2. In fact, when I am adding potassium metabisulfite powder to wine, getting a whiff of it feels like it sucks the air right out of my lungs. This doesn’t mean I am allergic to it, because it occurs in much lower levels in the wine than it does in the powder form. It’s just nasty, toxic stuff (the EPA has classified it as an air pollutant). The truth is, most people are NOT allergic to it, and most people who experience wine headaches are actually having a reaction to the histamines that occur naturally in red wine as a byproduct of the fermentation process, and not the SO2.

My own opinion on the topic differs, though. If I drink a wine high in SO2, I get a raging headache that just won’t quit. I usually get this from white and rosé wines, and not red wines (although red wines make me feel a little congested sometimes). I am convinced that high levels of SO2 can, in fact, cause headaches in some people. I don’t think ALL wine headaches are caused by SO2, but if you notice that commercial white wines give you a bad headache and red wines don’t, perhaps it could be the culprit…

What many people don’t know is that SO2 occurs naturally in all fermented wine, since it’s a natural byproduct of the fermentation process. The active yeasts actually create SO2 in minuscule quantities during fermentation, and any sulfur sprayed in the vineyard during the growing season can also add to the total amount of SO2 in a finished wine. That’s why most (but not all) commercial wine bears “contains sulfites” on the label. If a wine contains less than 10ppm SO2, technically they do not need to put it on the label, however most producers do – even if their wine is within the threshold – to avoid any red tape with regulatory agencies.

Wine isn’t the only food product that contain sulfites. Dried fruits, processed foods such as bread and tortillas, and many other things (mostly processed) contain sulfites to keep them fresh and palatable. In small doses, sulfites are relatively harmless (except to those with an allergy) and you’d probably never know that you were eating or drinking them. I wouldn’t worry too much about it if you aren’t experiencing any discomfort, but in general we like to avoid food products and wine with preservatives and additives. Winelandia strives to curate wines with little or no added SO2 or other chemical additives.

In conclusion, sulfur dioxide is a complicated topic prone to controversy and it’s up to the consumer to ultimately decide their point of view on the topic. This is mine, and while I’m sure not everyone will agree with me, I hope that this blog post has helped you gain a better understanding of what this chemical compound is and what it does to your wine.

A special shoutout to Chris for helping me work out some of the finer details on this topic.