Hydrogen Sulfide (H2S) has been known to plague winemakers for centuries, but it needn't. Its causes are as simple as is its cure, if dealt with soon enough after detection.
There are three primary causes: ...
Hydrogen sulfide: the smell of rotten eggs or like substances often found in wines; may dissipate with aeration.
Kraut: perceived in many wines from the Merlot variety.
[edit] Hydrogen sulfide
Hydrogen sulfide (H2S) is generally thought to be a metabolic by-product of yeast fermentation in nitrogen limited environments. It is formed when yeast ferment via the sulfate reduction pathway.
Smell of Hydrogen Sulfide gas in wine. Thought to be a characteristic imparted by certain yeast strains. A decided flaw.
ROUGH
(see also ASTRINGENT). Flavor/texture is coarse. Acidity and/or tannin are predominant and unpleasant.
The odor of hydrogen sulfide (the additive to household gas that allows you to smell it escaping). Rare in wine, and most unfortunate when it occurs. Almost always attributed to poor handling of grapes and the wine during production.
Hot
High in alcohol, producing a slightly burning sensation on the palate. Generally undesirable except in fortified wines.
Hydrogen sulfide
Chemical responsible for the "off" odor of rotten eggs in wine.
These compounds can be considered "volatile" like aldehydes, ethyl acetate, ester, fatty acids, fusel oils, hydrogen sulfide, ketones and mercaptans) or "non-volatile" like glycerol, acetic acid, and succinic acid.
The added oxygen would also limit the reductive quality of Barbera and limited the occurrence of off-odors of hydrogen sulfide that would occur in some examples.
Usually through splashing while racking, sparging with air, or simply by stirring a container very vigorously. This is sometimes done to "blow off" undesirable aromas such as hydrogen sulfide or to give an initial dose of oxygen to a fermentation ...
This was a vintage with widespread "stuck" fermentations and high levels of hydrogen sulfide. However, many winemakers overcame these problems and the best reds were ripe and balanced and their varietal character only diminished by high alcohol.
" It is sometimes instructive to think of the reduced state as "negative oxidation." In wine, the reduced state is usually recognized by the obvious smell of rotten eggs (hydrogen sulfide, or H2S) which nearly always accompanies the reduced state.
OFF ODORS - May include smells that are unpleasant, but usually limited to wine flaws such as the pungency of Sulfur Dioxide (like a burnt match head), Hydrogen Sulfide (rotten eggs), cork taint (like a moldy cellar), vinegar, ...
tasting the strongest or most appealing wine, but it provides a chance to form a more definite impression of the lightest-smelling wines, without being overwhelmed by the "bigger" wines. Wines that have suspected defects, such as hydrogen sulfide ...
 See also: Fermentation, Wine, Grape, Acid, Character
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