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What does it mean when a wine smells like rotten egg, burnt rubber, cabbage, garlic, or canned corn? In this episode of The Wine Lab, Dr. Andreea Botezatu explores sulfur and reductive faults in wine, explaining what wine professionals mean by “reduction,” why these aromas appear, and how they can evolve over time. Along the way, she looks at hydrogen sulfide, mercaptans, thiols, disulfides, and even the old copper penny trick, all through the lens of clear, consumer-friendly wine science. If you have ever opened a bottle and wondered whether something had gone wrong, this episode will help you understand what your glass may be telling you.

Glossary

Reduction / Reduced wine
A practical wine term used for sulfur-related off-aromas that can make a wine smell closed, sulfurous, or unpleasant.

Volatile sulfur compounds
A family of sulfur-containing aroma compounds that can strongly affect how a wine smells.

Hydrogen sulfide (H₂S)
A sulfur compound associated with a rotten egg smell. It is often the easiest sulfur fault to recognize.

Mercaptans
An older cellar term for certain sulfur compounds linked to aromas such as garlic, onion, cabbage, rubber, or skunky notes.

Thiols
The more modern chemical term for the same family of compounds often called mercaptans. Some thiols are desirable in wine, while others are faults.

Disulfides
Compounds that can form when mercaptans react with oxygen. They often have higher sensory thresholds, which can make a sulfur problem seem to fade even though it has not fully disappeared.

Detection threshold
The concentration at which a compound becomes noticeable by smell or taste.

Redox
Short for reduction-oxidation chemistry. In wine, it relates to the balance of oxidative and reductive reactions that influence aroma and stability.

Bench trial
A small-scale test carried out before making a treatment decision on a whole tank or lot of wine.

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