Hydrogen sulfide (H2S) is a well-known contaminant found in some wines that have so-called reductive off-odors. H2S, described as ‘rotten egg-like aroma’, brings the biggest trouble to wine maker. H2S is produced by the sulfate reduction sequence (SRS) pathway in S. cerevisiae during alcoholic fermentation. Very low levels of H2S can be detected due to its low odor threshold. It can be masking the fruity character of wine below sensory threshold, so trace amounts can have a serious effect on final wine quality.
There are several factors effect H2S production, such as deficiency of yeast assimilable nitrogen, insufficiency of pantothenic acid or pyridoxine. The deficiency of sulfur containing amino acids can trigger yeast to synthesize H2S from inorganic sulfur compounds.
Compounds derived from H2S
Mercaptanes (R-S-H)
Garlic, burnt rubber, rotten cabbage
Mercaptaneproduces a garlic, burnt rubber, cooked cabbagein wine. Thosecompounds are produced by the interaction of H2S with other wine components such as ethanol during wine fermentation or aging.
Disulfides (R-S-S-R)
Burnt rubber, garlic, cabbage, onion-like
Disulfides are formed from oxidation of sulfide or mercaptan precursors and very difficult to remove from wine，it can be reverted back to mercaptans with the addition of SO2.
Table1. Sulfur compounds for reduction odors
Sulfur compounds | Perception thresholds(ug/l) | Description |
Hydrogen sulfide | 0.8 | Rotten eggs |
Methanethiol | 0.3 | Rotten cabbage, burnt rubber |
Ethanethiol | 1.1 | Onion, garlic, rubber |
Dimethyl sulfide | 25 | Canned corn, asparagus |
Dimethyl disulfide | 0.9 | Asparagus, garlic, rubber |
Dimethyl disulfide | 29 | Vegetables, onion |
Ethyl disulfide | 4.3 | Onion |
Positive sulfur compounds
Fruity varietal Thiols
Box tree, passion fruit, grapefruit
Varietal thiols(4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexyl acetate (3MHA), and 3-mercaptohexan-1-ol (3MH)) have a positive impact on wine aroma and flavor. These volatile thiols are common in Sauvignon Blanc, but also have been found in other grape varieties such as Riesling, Cabernet Sauvignon, Merlot, and Semillon.
Table 2. Fruity thiols
Volatile thiols | Perceptionthreshold (ng/L) | Description | Range in wines (ng/L) |
4-methyl-4-mercaptopentan-2-one (4MMP) | 0.8 | Box tree, passion fruit, black current | 0-40 |
3-Mercaptohexan-1-ol (3MH) | 60 | Grapefruit, passion fruit | 50–19,000 |
3-mercaptohexylacetate (3MHA) | 4 | Passion fruit, box tree, guava | 0–100 |
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Published by Fang Fang |
