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
Off-Flavors
Geranium Leaf Smell (Geraniol Off-Flavor)
Root Cause
Malolactic bacteria (MLF) metabolizing Potassium Sorbate added to sweeten or stabilize.
Step-by-Step Resolution
1. Geranium off-flavor cannot be removed once formed.
Prevention Tip: NEVER add Potassium Sorbate if Malolactic Fermentation (MLF) is active or incomplete; ensure SO2 inhibits MLF first.
Off-Flavors
Green Apple / Raw Pumpkin Aromas (Acetaldehyde)
Root Cause
Premature racking before yeast cleans up intermediate acetaldehyde, weak yeast health, or SO2 over-sulfiting.
Step-by-Step Resolution
1. Keep brew on active yeast lees (diacetyl/acetaldehyde rest) at 68°F–72°F for 7-14 additional days.
2. Krausen with fresh active yeast starter if lees were removed.
Prevention Tip: Never rack or cold-crash until yeast has fully completed primary fermentation and rested.
Off-Flavors
Harsh Fusel Hot Alcohol Burn
Root Cause
Fermenting Lalvin D47 or ale strains above 70°F, severe yeast stress, or excessive nitrogen/DAP additions.
Step-by-Step Resolution
1. Bulk age for 6 - 18 months in carboy (fusel alcohols esterify into smooth compounds over time).
2. Slightly sweeten (backsweeten) to mask harshness.
Prevention Tip: Control fermentation temperature within the lower half of the yeast's ideal range.
Off-Flavors
Medicinal / Band-Aid / Chlorophenol Smell
Root Cause
Using chlorinated tap water (chlorine/chloramines reacting with polyphenols to form chlorophenols) or wild yeast infection.
Step-by-Step Resolution
1. Chlorophenols cannot be removed once formed.
2. Use for cooking or distill under legal permit.
Prevention Tip: ALWAYS use spring water, RO water, or treat tap water with 1/2 Campden tablet per 20 gal to neutralize chloramines.