Why Sulfur Faults Can Persist in Wine and How Targeted Treatment Changes the Game
Sulfur-related off-aromas in wine remain a persistent challenge for winemakers worldwide. From the rotten-egg notes of hydrogen sulfide (H₂S) to the cabbage, or garlic and onion aromas of mercaptans (thiols) and the heavy rubbery or burnt matches of disulfides, these compounds can undermine quality and consumer enjoyment.
Understanding why these faults form and why traditional remedies sometimes fail is key to better control.
The Chemistry Behind Sulfur Off-Aromas
At its core, sulfur chemistry in wine is dynamic:
Hydrogen sulfide (H₂S) is often produced during fermentation when yeast reduce sulfate or sulfite. It is small, polar, volatile and detectable even at low concentrations.
H₂S can react with ethanol and other wine constituents to form mercaptans (thiols). These are slightly larger and less volatile molecules that carry distinctive off-aromas like garlic, onion, rubber, or burnt rubber.
Mercaptans can further oxidize or couple together to form disulfides which are larger, less volatile, and more hydrophobic compounds with a more potent and persistent sensory impact.
This cascade can proceed in both directions: disulfides can, under some conditions, break back down to mercaptans. However, the equilibrium often favors formation of heavier sulfur species over time.
Where Copper Fits, and Where it Doesn’t
For decades, elemental copper has been the frontline defense against sulfur impacted wines, particularly:
Copper binds readily with H₂S and certain small mercaptans, forming insoluble copper-sulfur complexes that are removed from wine.
But copper has limitations:
It is less effective with larger, hydrophobic sulfur molecules, especially disulfides and higher mercaptans. Their compound structures are more complex which can result in reduced reaction rates and interactions with copper.
Overuse of copper can strip desirable thiols and create unbalanced sensory profiles. Regulatory limits and concerns about residual copper constrain how much can be used.
As a result, wines with significant levels of disulfides or complex mercaptan mixtures often remain “stuck” despite standard copper fining.
Why Sensory Impact is a Function of More Than Just H₂S
Though winemakers may think in terms of individual faults, consumers perceive a holistic sulfurous character. Small amounts of multiple sulfur compounds can interact synergistically to produce a general sense of skewed aroma, even when no single compound is above its detection threshold.
Moreover, because larger sulfur species are less volatile, they can persist longer over time and continue to contribute to sensory faults well after initial treatment.
This explains an observation: wines treated with copper appear to improve, yet upon aging or bottle opening they can exhibit sulfur-related flaws.
A Targeted Approach: Thiol Chemistry
amaea’s molecularly imprinted polymers (MIPs) are a filtration media, engineered to have binding sites shaped and tuned for specific target molecules.
In the case of sulfur compounds, amaea MIPs have been designed with cavities that match the size, shape, and polarity of thiols and disulfides. These cavities act like a lock for these sulfur molecules resulting in selective adsorption that preferentially removes the more problematic, larger, and less copper-responsive sulfur species — without stripping desirable aroma compounds.
Why Combined Treatments Make Sense
From a practical standpoint, winemakers can benefit from a two-stage approach:
Targeted removal of larger sulfur compounds (disulfides and heavier mercaptans) via amaea MIP-based methods.
Traditional copper fining to address residual H₂S and smaller mercaptans.
By reducing overall sulfide impacts, particularly those that copper struggle with, the subsequent copper treatment can work more effectively, at lower doses or is sometimes not required at all.
The Bigger Picture
amaea MIPs represent a shift from broad, non-specific fining toward precision chemistry in wine fault management.
Understanding the molecular behavior of H₂S, mercaptans, and disulfides helps explain why some wines remain stubbornly sulfurous despite best practices and suggests a path forward that aligns with both sensory science and modern enology.
Authors: Dr Aaron Low - Chief Technical Officer, Dr Sylvia Baars - Head of Science, Dr Maxime Savoie - Senior Developer