Sulfites in Wine: What They Are and Why They Matter

Winemakers have used sulfur for centuries.

The Romans burned sulfur candles in barrels to keep wine from turning to vinegar. Some written references to SO₂ in European cellars date back to the 1400s.

What has changed isn’t the idea — it’s how precisely (and how much), sulfur is used in modern winemaking.

Today, sulfites in wine are used as a preservative to protect freshness and flavor. Some see them as essential; others believe they dilute the natural essence of wine. The latter view has coincided with the rise of natural or “RAW” wines, which often avoid sulfites (and other additives) in pursuit of purity.

But here’s the truth: “natural” doesn’t always mean sulfite-free.

Yeast naturally generates SO₂ during fermentation, so nearly every wine contains some sulfites. The real difference is whether a winemaker chooses to add more (and why).

While some question their health effects when mixed with alcohol, sulfites aren’t an issue for most people. Governments enforce labeling and limits so that the few who are sensitive (often those with asthma) can make informed choices.

The better question is how sulfites affect a wine’s character, and whether there are other ways to preserve liveliness in the glass.

That’s where farming makes a difference. Healthy vineyards with a commitment to biodiversity can produce wine that feels more vivid on its own — whether it includes a touch of sulfur or not.

In this guide, we’ll demystify sulfites: what they are, how they work, and how thoughtful farming and winemaking shape a wine’s final character, regardless of additives.

“Growing and making natural wine is…a choice based on wanting to produce a drink that pulsates with life, driven by a deep respect for both nature and life itself. Wines made like this are no-added sulfite wines, yes, but they are so, so much more than that too. They are what truly great wine is all about.” - Isabelle Legeron MW, Founder of RAW WINE

What Are Sulfites (SO₂) in Wine?

Sulfites are compounds that include sulfur dioxide (SO₂) and related salts like sodium or potassium metabisulfite. They’re widely used as additives in food (including wine) but also appear naturally in many fermented products — and even naturally in our bodies.

In modern winemaking, sulfites serve two main roles:

• Antioxidant: They shield wine from oxidation, which spoils color and tastes, causing it to lose those fresh fruit aromas.

• Antimicrobial: They help keep harmful microbes at bay, so wine stays safe and flavorful over time.

Sulfites vs. Sulfides vs. Sulfates

To avoid confusion, let’s first distinguish between similar terms:

• Sulfites (like SO₂) are oxidized sulfur compounds used to preserve and stabilize wine.

• Sulfides are reduced sulfur compounds (often unwelcome) forming off-odors like rotten egg or cabbage during fermentation when yeast metabolism goes awry.

• Sulfates are fully oxidized sulfur forms with different chemistry altogether (not typically relevant to wine preservation).

Why Are Sulfites Used?

In addition to preserving freshness and preventing spoilage, sulfites also keep wine stable.

As an additive, they provide the consistency and longevity needed to distribute wines across a wider region. This stability also allows bottles to age gracefully without losing their intended style.

A key part of the winemaker’s job is managing free and bound SO₂ alongside acidity to guard each glass against spoilage while keeping the wine fresh and expressive.

Free vs. Bound SO₂ — What’s the Difference?

Why do some wines stay fresh longer while others spoil quickly? It all comes down to the balance of oxygen and sulfur dioxide (SO₂). Oxygen drives both aging (and loss of freshness). SO₂ binds with it to slow that process. A wine’s ultimate aging potential depends on how much SO₂ is free versus bound, and how much oxygen remains in the bottle for the SO₂ to counteract. 

Free SO₂ refers to the portion of sulfites that remains active and unbound. It includes both:

• Molecular SO₂ (the actual gas dissolved in the wine); the most active form.

• Bisulfite (HSO₃⁻) and sulfite (SO₃²⁻) ions that are in equilibrium with molecular SO₂.

Bound SO₂ results when sulfites attach (bind) to other wine components (like pigments or acetaldehyde) making them inactive and no longer able to protect the wine.

Why pH Matters (and How It Impacts Sulfite Activity)

A wine’s acidity directly affects how well sulfites can do their job. The lower a wine’s pH (meaning the more acidic), the more of its sulfites exist in the powerful molecular SO₂ form (the version that best protects against spoilage).

For example, at pH 3.5 you’ll have about twice as much molecular SO₂ as at pH 3.8, even if the total free SO₂ is the same. Most wines fall between pH 3.0 and 4.0, but once the pH rises above 4.0, very little remains in that active molecular state.

This is why high-acid wines (like Riesling) often need less added SO₂, while lower-acid wines may require more protection to stay fresh and stable.

In some cases, sulfites are also used to block malolactic fermentation, where tart malic acid becomes softer lactic acid. This allows producers of crisp wines (like Sancerre) to maintain a zesty, fresh style.

Sulfite Labeling and Regulatory Standards

Knowing sulfite labeling rules helps you read between the lines when a wine is labeled “natural” or “organic.” However, rules can vary by location and circumstance.

U.S. Regulations

Since 1987, the U.S. has required any wine with 10 ppm or more of total sulfites to clearly display the phrase “Contains Sulfites” on its label.

The federal limit allows wines to contain a maximum of 350 ppm of sulfites. This covers nearly all styles from crisp whites to fortified dessert wines.

EU Regulations

In the European Union, the same labeling rule applies: if a wine has 10 ppm or more, it must state “contains sulfites.”

However, maximum sulfite levels vary by wine type:

• Red wines: up to 150 mg/L

• White & rosé wines: up to 200 mg/L

• Sweet wines: as high as 400 mg/L, depending on residual sugar

Organic Wine Rules

Organic labeling adds another layer of complexity.

In the U.S., wines labeled simply as “Organic” cannot have any added sulfites. They may still contain trace amounts, but only the naturally occurring sulfites from fermentation (less than 10 ppm).

On the other hand, bottles labeled “Made with Organic Grapes” allow winemakers to add sulfites, though the total cannot exceed 100 ppm.

The European Union takes a slightly different approach. Organic wines there may include added sulfites, but at reduced levels compared to conventional wines. For example, red organics often cap out around 100 mg/L, and whites or rosés around 150 mg/L.

Common Sulfite Myths (Debunked)

When it comes to sulfites in wine, there are plenty of myths swirling around. But here’s the truth about sulfites:

Myth 1: Sulfites cause headaches.

Fact: There’s little scientific evidence linking sulfites directly to headaches. The more likely culprits are histamines, tannins, and dehydration.

Also, compounds like quercetin can trigger reactions in some people. Think about it this way: other foods like dried fruit often contain much higher levels of sulfites, but few people complain about headaches after eating dried apricots.

For the vast majority of wine drinkers, sulfites are not a health concern.

The people most at risk are those with asthma or a confirmed sulfite sensitivity. However, their reactions typically show up as respiratory issues, skin hives, or digestive upset — not headaches.

Myth 2: Red wine has more sulfites than white wine.

Fact: It’s actually the opposite. Red wines usually need less added sulfites because their tannins and other natural phenolics act as preservatives.

White wines, lacking those natural defenses, are more prone to oxidation and microbial spoilage. Winemakers often add more sulfites to keep whites fresh and stable.

Here’s a general comparison:

Most everyday wines fall toward the lower-middle end of these ranges. Only very sweet or highly stabilized wines push toward the upper limits, since higher sugar and ongoing fermentation activity make them more vulnerable.

Myth 3: European wines contain fewer sulfites than U.S. wines.

Fact: While EU maximum limits are often lower than U.S. standards, the actual sulfite levels in wines from both regions tend to overlap.

The perception that European bottles are sulfite-free comes from labeling differences. But many wines contain comparable levels, even if the regulations look stricter on paper.

Myth 4: Organic or natural wine is sulfite-free.

Fact: All wines naturally contain some sulfites because yeast produces SO₂ during fermentation. Even organic wines can contain trace amounts.

Many wine bottle certifications allow limited sulfite presence, but the term “natural” wine has no legal definition. Some makers add no sulfites at all, but others use small amounts to ensure stability.

While many choose to use fewer additives, sulfites are usually present to some degree.

The Real Benefits of Natural Wine

It’s clear that sulfites, no matter how you feel about them, are almost always present in wine. But this raises a question: If sulfites don’t pose much of a health concern (and can even benefit production), then what’s the point of making “natural” or “raw” wine?

The answer lies in how winemakers approach farming, microbiology, and the very idea of what makes wine feel alive.

Wine Microbiology

At its core, wine is alive because of its microbiology. Yeasts and bacteria from the vineyard transform grape juice into something complex and expressive.

When winemakers add large amounts of sulfites to prevent spoilage, they also suppress that microbiology. The more sulfites used, the less vibrant and expressive the wine can feel.

This is why natural wine resonates with so many drinkers. By limiting additives, it seeks to protect that vitality and preserve the organisms that shape flavor, resulting in a vivid, living character in the glass.

Some winemakers even go further, attempting to remove naturally occurring sulfites altogether. But isn’t stripping out what nature already provides just as unnatural?

The Problem With No-Sulfite Wine

Many conventional winemakers are rethinking their use of sulfites. But in order to ensure the safety of their products, they simply replace them with other additives like lysozymes or ascorbic acid.

Others use pasteurization, sterile filtration, or UV treatment for similar effects. But these methods can (sometimes) be more heavy-handed than using sulfites.

The bigger issue is this: Wine has slowly become less about taste and more about control.

In trying to make wine a predictable, repeatable experience, we’ve forgotten that wine is a living product born from natural transformation. True natural wine isn’t about sulfite-free labels. It’s about vitality, diversity, and balance. Heavy sulfite use can mute those qualities, but swapping them for other harsh additives or sterile technologies can do the same.

The goal isn’t lifeless predictability — it’s wine that tastes like a living expression of the vineyard.

So what can we do to preserve that dynamic?

Focus on Farming: The Leap of Faith

“The most important thing, above all, is to get the farming right so that you have such a healthy harvest and an abundance of indigenous microbiology that doing away with the sulfites just takes a leap of faith.” - Isabelle Legeron MW, Founder of RAW WINE

Going low-sulfite means more than removing additives — it also includes healthy farming. Robust vineyards contain stronger microbiology that can carry fermentation without chemical backup.

That’s why some producers, like Eduard and Stephanie Tscheppe-Eselböck of Gut Oggau in Austria, only went sulfite-free after years of biodynamic work. As they put it, the hardest part is “letting go” and trusting the vineyard to do its job.

Producing great no-added-sulfite wine requires this leap of faith. But when farming promotes biodiversity and soil health, the wine can stand on its own.

That’s what makes natural wine special: not simply the absence of sulfites, but the presence of life. It creates a vibrancy and purity that can’t be faked.

FAQ

What exactly are sulfites in wine?

Sulfites are sulfur-based compounds, mainly sulfur dioxide (SO₂), that occur naturally during fermentation. They are often added by winemakers to prevent oxidation and spoilage and to help preserve freshness and stability in wine.

Do sulfites in wine cause headaches?

Sulfites are not a proven cause of wine headaches. More likely culprits include histamines, tannins, or dehydration (or other natural compounds in wine). Only a small group of people (often with asthma) experience true sulfite sensitivity.

Are organic or natural wines sulfite-free?

Not entirely. All wines contain at least some natural sulfites from fermentation. In the U.S., organic wines cannot have added sulfites, while “Made with Organic Grapes” wines may include small amounts. “Natural wines” vary widely, since the term isn’t regulated.

How can I tell if a wine has sulfites?

In both the U.S. and EU, wines with more than 10 ppm must carry a “Contains Sulfites” label. Nearly all commercial wines meet this threshold, so you’ll see the warning on most bottles.

I’m sensitive to sulfites. What should I look for?

If you have confirmed sulfite sensitivity, seek out wines labeled “Organic” in the U.S. (no added sulfites) or natural producers who specify low-sulfite practices. You may also do better with reds, which typically have lower sulfite levels than whites.

Final Thoughts: Sulfites in Perspective

Sulfites are a helpful tool in wine preservation. They’re safe for most people and likely not the culprit behind your wine headaches.

But, as with many modern winemaking techniques, some wine enthusiasts feel additives like this dilute the character of wine.

In contrast, natural wines aim to let the character of the vineyard thrive from grape to glass. Their vibrancy and authenticity come from clean farming, biodiversity, and the winemaker’s trust in the vineyard.

However, you might be thinking, “Can you really taste the difference?”

Ask any sommelier, and the answer is absolutely, “Yes.” But for the average wine drinker, picking up (and describing) the subtle differences of terroir require more than a casual tasting.

Napa Valley Wine Academy (NVWA) helps people from all backgrounds deepen their understanding of wine. As America’s most awarded Wine & Spirit Education Trust (WSET) school, NVWA provides the tools and training to expand your wine knowledge and appreciation.

Want to go further? Explore WSET courses (online or in person) and discover a richer wine experience.

Special thanks to Isabelle Legeron MW (and her book Natural Wine: An Introduction to Organic and Biodynamic Wines Made Naturally) for significant contributions to this article.