Fermentation Off-Flavor & Defect Troubleshooter
Diagnose rotten egg sulfur smells, DMS, stalled fermentations, haze, and harsh fusel alcohols with certified BJCP/WSET resolution steps.
All Defects
Sulfur & Aromas
Oxidation & Contamination
Fermentation Health
Off-Flavors
Clarity & Appearance
Sulfur & Aromas
Burnt Rubber / Garbage / Skunk (Mercaptan & Ethanethiol)
Root Cause
Severe prolonged yeast autolysis in the presence of unremoved H2S, reacting to form ethanethiol and mercaptans.
Step-by-Step Resolution
1. Immediately rack off gross yeast lees.
2. Dose with copper sulfate (0.5 to 1.0 ppm max under winemaking guidelines).
3. Aerate gently after copper treatment.
Prevention Tip: Treat H2S rotten egg smells promptly before they evolve into irreversible mercaptans.
Sulfur & Aromas
Cooked Corn / Cabbage (DMS - Dimethyl Sulfide)
Root Cause
S-methylmethionine (SMM) precursor in malt/grain or heated must, covered boil during wort preparation, or slow chilling.
Step-by-Step Resolution
1. CO2 scrubbing: purge the vessel with CO2 from the bottom to drive off volatile DMS gas.
2. In future batches, boil with lid completely off.
Prevention Tip: Boil wort uncovered for at least 60-90 minutes and chill rapidly below 70°F.
Sulfur & Aromas
Rotten Egg / H2S Hydrogen Sulfide Smell
Root Cause
Yeast nitrogen starvation (insufficient YAN), high gravity stress, or high temperature fermentation.
Step-by-Step Resolution
1. Splash aerate vigorously if early in fermentation (before 1/3 sugar break).
2. Add Fermaid O or DAP if within active primary.
3. Stir with a clean copper wire/spoon to bind hydrogen sulfide into copper sulfide crystals.
Prevention Tip: Calculate YAN needs using the Nutrient Calculator and follow a Staggered Nutrient Addition (TOSNA) schedule.