Management of Reductive Odours in Wine
Reductive odours during fermentation can damage a wine with otherwise good potential. For that reason frequent daily monitoring of fermenting juice or must for detection of off-odours is justified, particularly near the end of fermentation.
Measures that can be taken when reductive odours are detected:
A A simple method of eliminating a reductive odor is to supplement nutrition with small amounts of combined nutrient or DAP and to continue monitoring. This usually does the trick.
B Where nutrition is not sufficient to solve the problem consider vigorously splashing and racking of the wine to drive off odours and introduce oxygen into the wine. Do this twice a day or more. It is surprising how effective this is and it may be repeated until the wine is close to a specific gravity of 1.01 or less.
C At times this too is insufficient, strange funky odours still persist and more drastic need to be undertaken post fermentation. Some amateur winemakers expose wine to copper coils or copper scrub pads to eliminate reductive odours. The concern is that copper can be toxic in high levels and by exposing wine to elemental copper for long periods of time the final concentrations in wine are unknown. Legal limits for copper concentrations in many jurisdictions is 0.5 mg/L. A more reliable method of making copper additions is to use copper sulphate.
Here are two informative articles available to guide a winemaker in copper sulphate additions. They may or may not be effective, but then again drastic measures are warranted if the first two measures are not successful.