How H2S is formed

Hydrogen sulphide (H2S) can come from different sources.

  • Sulfur used in the vineyard (e.g. for battling powdery mildew) too close to harvest. The reductive conditions that are created during fermentation can chemically convert this sulfur to hydrogen sulfide.
  • Volatile sulfide formation can occur during the active phase of fermentation or as the wine ages on yeast lees post-fermentation.
  • But the majority of H2S produced occurs during the process by which Saccharomyces makes sulfur-containing amino acids.

Hydrogen sulphide production varies depending on:

  • Growth conditions of the yeast
  • Environmental and nutritional factors
    • levels of elemental sulphur
    • presence of sulphur dioxide
    • organic compounds containing sulphur
    • nitrogen limitation and
    • vitamin deficiency