REDUCTION
Identification
Smell
rubber
rotten egg
rotten
cabbage
boiled cauliflower
plastic
sewage
garlic
onion
Place of occurrence
winery
consumer packaging
Cause of occurrence
Reduction of sulphur dioxide (SO2) and sulphate (SO4(2-)) used as antioxidants to hydrogen sulphide (H2S). The odours associated with this defect are caused by sulphur derivatives (S) and are based on traces of hydrogen sulphide (H2S), mercaptans or thiols
Excessive copper (Cu) content in wine leads to yeasts trying to neutralise this excess during fermentation, precipitating it in the form of copper sulphide (CuS), form hydrogen sulphide (H2S)
Elemental sulphur (S) remaining on grape berries after treatments in the vineyard against fungal diseases and subsequent reduction to hydrogen sulphide (H2S) during and after alcoholic fermentation
Use of wild yeasts for alcoholic fermentation, forming a high level of hydrogen sulphide (H2S)
Catabolism of yeast protein by proteolytic enzymes with the release of hydrogen sulphide (H2S)
Anaerobic winemaking (without contact with oxygen (O2))
Nutritional deficiency of yeasts (nitrogen (N)) during fermentation
Use of oxygen-tight closure (screwcap)
Counteraction
Maintaining the proper level of nitrogen (N) in the wine during fermentation (addition of nitrogen (N) by diammonium phosphate (NH4)2HPO4)
Reducing the concentration of elemental sulphur (S) in the must
Use of commercial yeasts for alcoholic fermentation that have a low tendency to form hydrogen sulphide (H2S)
Controlling the permissible level of copper (Cu) in wine during fermentation
Addition of an acceptable amount of copper sulphate (CuSO4) or fining agents based on the autolysis of yeasts into wine with reductive notes
Controlled contact of wine with oxygen (O2) during winemaking operations
Use of closures that allow an acceptable amount of oxygen (O2) ingress