Why Your Wine Smells Like Rotten Eggs: H2S Fixes Before It’s Too Late

Your wine smells like rotten eggs or burnt matches. Panic sets in. But hydrogen sulfide (H2S) is treatable if caught early—and completely preventable with proper technique.

What Causes H2S

Yeast produce hydrogen sulfide when stressed. The sulfur they naturally process gets converted to H2S instead of being incorporated into proteins. Common stressors include:

• Nitrogen deficiency: Yeast need nitrogen to build proteins. Without it, sulfur metabolism goes wrong.
• High temperatures: Stressed, overheated yeast produce more H2S.
• Extended contact with lees: Dead yeast break down, releasing trapped sulfur.
• Certain yeast strains: Some are more prone to H2S than others.
• Elemental sulfur on grapes: Residual vineyard sprays provide sulfur for H2S formation.

Detection and Assessment

Mild H2S: Faint struck match or rubbery smell. Often dissipates with aeration.

Moderate H2S: Obvious rotten egg smell. Needs intervention but is fixable.

Severe/evolved: Mercaptans and disulfides form from untreated H2S. These smell like burnt rubber, garlic, or onions and are much harder to treat.

Early Intervention (During Fermentation)

If you detect H2S during fermentation:

1. Add yeast nutrient: Diammonium phosphate (DAP) provides nitrogen. Add immediately.
2. Aerate gently: Splash racking introduces oxygen that helps dissipate H2S.
3. Check temperature: Cool fermentation if running hot.
4. Rack off gross lees: Reduce contact with sediment.

Act quickly—H2S evolves into worse compounds if left untreated.

Post-Fermentation Treatment

If H2S persists after fermentation ends:

Copper treatment: Copper sulfate binds with H2S, forming insoluble copper sulfide that settles out. This is the most effective treatment but must be done carefully—excess copper is toxic and can cause instability.

Process:

1. Make a 1% copper sulfate solution
2. Bench trial: add increasing amounts to small samples
3. Smell each sample after 10 minutes
4. Use minimum effective dose on full batch
5. Test final copper level (should be under 0.5 ppm)

Ascorbic acid: Sometimes used in combination with copper. Reduces oxidation and helps copper work.

Preventing H2S

• Use yeast nutrients (DAP, Fermaid) from the start
• Choose low-H2S yeast strains for problem grapes
• Maintain appropriate fermentation temperature
• Rack promptly after fermentation
• Monitor for sulfur smell throughout fermentation

When It Is Too Late

If H2S has evolved to mercaptans (burnt rubber, garlic, cooked cabbage), treatment becomes difficult. Copper may help somewhat, but the wine is usually permanently compromised. Prevention truly is the only reliable cure.