Wine Faults Detection

Introduction

Wine faults are defects that negatively impact wine quality, ranging from subtle character changes to wines rendered undrinkable. For enologists, the ability to detect faults early, understand their causes, and implement prevention strategies is fundamental to quality winemaking. Some “faults” exist on a spectrum—small amounts adding complexity while larger amounts become defects (e.g., volatile acidity, Brettanomyces). This guide covers the major wine faults, their sensory characteristics, analytical detection methods, causes, and prevention strategies.

Oxidation Faults

Excessive Oxidation

Sensory Characteristics:

Whites: Brown/amber color; nutty, sherry-like, flat, bruised apple
Reds: Brick/brown color; dried fruit, prune, loss of freshness

Causes:

Inadequate SO₂ protection
Excessive oxygen exposure during processing
Poor closure seal (cork failure)
Tank/barrel headspace
Premature aging (premox in white Burgundy)

Detection:

Visual: Color assessment
Sensory: Trained panel
Analytical: Acetaldehyde levels (>100 mg/L concerning)

Prevention:

Adequate free SO₂ maintenance
Inert gas blanketing
Minimize pump-overs/transfers
Appropriate closure selection
See oxidation management

Premature Oxidation (Premox)

Description: Unexpected early oxidation in wines that should age

Affected: Particularly white Burgundy (2000s crisis), especially Chardonnay

Causes: Debated—closure variation, winemaking factors, grape composition

Detection: Premature browning, flat aromatics in young wines

Reduction Faults

Hydrogen Sulfide (H₂S)

Sensory Characteristics: Rotten eggs, sewage, struck match

Threshold: 1-2 µg/L (very low)

Causes:

Yeast stress during fermentation
Nitrogen deficiency
Heavy lees contact
Reductive winemaking (excessive)

Detection:

Sensory: Very distinctive aroma
Analytical: Gas chromatography

Treatment:

Copper sulfate addition (up to legal limits)
Aeration
Racking from lees

Prevention:

Adequate YAN (yeast assimilable nitrogen)
Healthy yeast nutrition
Temperature management
See reduction management

Mercaptans (Thiols)

Sensory Characteristics: Onion, garlic, rubber, burnt rubber, cabbage

Compounds: Methanethiol, ethanethiol, dimethyl sulfide

Threshold: Very low (0.3-50 µg/L depending on compound)

Causes:

H₂S evolution (more serious)
Protein breakdown
Lees-derived

Treatment:

Copper addition (limited effectiveness)
Aeration (may help some)
Prevention is key

Prevention: Same as H₂S; avoid post-formation

Disulfides

Sensory Characteristics: Cooked cabbage, canned vegetables, rubbery

Compounds: Dimethyl disulfide, diethyl disulfide

Cause: Oxidation of mercaptans

Treatment: Difficult; reduction to mercaptans then copper

Prevention: Address H₂S/mercaptan issues early

Microbial Faults

Brettanomyces

Sensory Characteristics:

Low levels: Spice, leather, earthy, savory (can be positive)
High levels: Band-aid, medicinal, barnyard, mouse, fecal

Key Compounds: 4-Ethylphenol (4-EP), 4-Ethylguaiacol (4-EG)

Thresholds:

4-EP: 400-600 µg/L (recognition)
4-EG: 50-150 µg/L

Sources:

Infected barrels
Fruit flies
Poorly cleaned equipment
Indigenous on grapes

Detection:

Sensory: Trained panel
Analytical: GC-MS for 4-EP/4-EG
Microbiological: Plating, PCR

Prevention:

Adequate free SO₂ (>30 mg/L molecular)
Low pH beneficial
Hygiene and sanitation
Barrel management
See Brett control

Volatile Acidity (VA)

Sensory Characteristics: Vinegar, nail polish remover, sharp

Compounds: Acetic acid, ethyl acetate

Thresholds:

Acetic acid: 0.5-0.8 g/L (style-dependent)
Ethyl acetate: 150-200 mg/L

Causes:

Acetobacter growth (oxygen exposure)
Some yeast strains
Stuck fermentation
MLF bacteria (some strains)

Detection:

Sensory: Distinctive
Analytical: Cash still; enzymatic; FTIR

Prevention:

Minimize oxygen exposure
SO₂ management
Sanitation
Complete fermentations
See VA prevention

Lactic Acid Bacteria Spoilage

Sensory Characteristics: Sauerkraut, mousy, geranium, butter (excessive)

Compounds: Various

Causes:

Uncontrolled LAB growth
Post-MLF spoilage
Residual sugar + LAB

Prevention:

Control MLF initiation
SO₂ post-MLF
Prevent residual sugar with LAB

Chemical Faults

Cork Taint (TCA)

Sensory Characteristics: Moldy, wet cardboard, musty, damp basement

Compound: 2,4,6-Trichloroanisole (TCA)

Threshold: 1-3 ng/L (extremely low)

Sources:

Cork (most common)
Winery environment (barrels, wood, drains)
Chlorine-based sanitation products

Detection:

Sensory: Trained panel
Analytical: GC-MS (very sensitive)

Incidence: 1-5% of cork-sealed wines (varies by cork quality)

Prevention:

Quality cork selection
Alternative closures
Avoid chlorine products
Environmental testing

Light Strike

Sensory Characteristics: Wet wool, wet dog, cooked cabbage (sulfurous)

Compound: Dimethyl disulfide (from riboflavin photodegradation)

Causes:

UV/visible light exposure
Clear or green bottles most susceptible
Sparkling wines particularly sensitive (see Sparkling Wine Production Challenges)

Prevention:

Dark bottles (brown most protective)
Avoid light exposure in storage/retail
UV-filtering packaging

Heat Damage

Sensory Characteristics: Cooked, stewed fruit, caramelized, maderized

Causes:

Excessive temperature during shipping/storage
“Cooked” wine

Detection:

Sensory: Premature aging character
Visual: Cork push; seepage

Prevention:

Temperature-controlled logistics
Appropriate storage
Consumer education

Fermentation Faults

Stuck Fermentation

Characteristics: Incomplete fermentation; residual sugar

Causes:

Nutrient deficiency
Excessive temperature
Alcohol toxicity
Osmotic stress (high sugar)
Toxic must components

Detection:

Density measurement
Residual sugar analysis
Yeast viability testing

Treatment/Prevention:

See stuck fermentation

Excessive Higher Alcohols (Fusel Oils)

Sensory Characteristics: Hot, solvent, harsh, burn

Compounds: Isoamyl alcohol, isobutanol, etc.

Causes:

High fermentation temperature
Nitrogen deficiency
Yeast strain

Prevention:

Temperature control (cool fermentation)
Adequate YAN
Yeast selection

Sensory Detection Protocol

Systematic Approach

Visual Assessment:

Color (oxidation, microbial)
Clarity (microbial, protein)
Viscosity (alcohol, sugar issues)

Aromatic Assessment:

First impression (fault or clean)
Identify fault type
Intensity rating
Evolution in glass

Palate Assessment:

Structural balance
Fault confirmation
Finish (faults often persist)

Reference Standards

Training Materials:

Commercial fault kits (Le Nez du Vin, etc.)
Spiked samples (known concentrations)
Regular calibration exercises

Detection Thresholds

Fault	Compound	Threshold
Cork taint	TCA	1-3 ng/L
H₂S	H₂S	1-2 µg/L
Brett	4-EP	400-600 µg/L
VA	Acetic acid	500-800 mg/L
Oxidation	Acetaldehyde	100-125 mg/L

Quality Control Program

Prevention Framework

Raw material quality: Grape health, equipment hygiene
Process control: Temperature, SO₂, oxygen management
Monitoring: Regular tasting, analytical testing
Documentation: Track issues for pattern recognition
Response protocols: Clear action plans for detected faults

Testing Schedule

Test	Frequency	Purpose
Free/Total SO₂	Weekly-monthly	Oxidation prevention
VA	Monthly	Microbial detection
pH/TA	Monthly	Stability monitoring
Sensory	Ongoing	Early fault detection
Brett (4-EP)	Quarterly (reds)	Contamination monitoring

Conclusion

Wine fault detection is a critical skill for enologists, requiring both sensory expertise and analytical knowledge. Early detection enables intervention before faults become irreversible, while understanding causes enables effective prevention. The best approach is proactive—maintaining optimal SO₂, controlling oxygen, practicing good hygiene, and monitoring wines regularly throughout production and aging.

References

Zoecklein, B.W. et al. (1999). “Wine Analysis and Production.” Springer. DOI: 10.1007/978-1-4757-6967-8
Ribéreau-Gayon, P. et al. (2006). “Handbook of Enology.” Wiley. Publisher Link
Waterhouse, A.L. et al. (2016). “Understanding Wine Chemistry.” Wiley. DOI: 10.1002/9781118730720

Last Updated: January 10, 2026
Research Grade: Technical reference
Application: Quality control, fault identification, prevention strategy