Wine Faults — Identifying Off-Flavours and Aromas
How to recognise and explain the most common wine faults in a certification exam context
Learning Objectives
- Identify the most common wine faults by smell and taste
- Explain the cause of cork taint, oxidation, reduction, and volatile acidity
- Distinguish between faulty wine and a wine that is simply outside your personal preference
- Use appropriate vocabulary to describe wine faults in a tasting note
Cork Taint (TCA)
The most famous wine fault, cork taint is caused by the compound 2,4,6-trichloroanisole (TCA), which can originate from natural cork. It creates a damp, musty, mouldy cellar smell — often described as wet cardboard or wet dog. TCA suppresses fruit aromas and makes the wine taste flat and lifeless. A corked wine cannot be fixed. The fault affects a small but significant percentage of wines sealed with natural cork, which is one reason for the widespread adoption of screw caps and synthetic closures.
Oxidation
Oxidation occurs when wine is exposed to too much oxygen — through a faulty cork, improper storage, or over-ageing. Oxidised white wines turn golden-brown, losing fresh fruit and developing flat, sherry-like, nutty, bruised apple characters. Oxidised red wines lose their bright ruby colour and develop brick/orange tones, with a flat, stale quality replacing fresh fruit. The compound acetaldehyde is associated with oxidation. Note: some wines (Sherry, Tawny Port, Madeira) are deliberately oxidised as a stylistic feature — this is not a fault.
Reduction
Reduction is caused by a lack of oxygen during winemaking, producing sulphur compounds including hydrogen sulphide (rotten eggs), mercaptans (onion, rubber, struck flint), and disulfides. A reductive wine can often be fixed by aerating it — pouring it vigorously into a decanter or swirling the glass. If reduction aromas dissipate after a few minutes in the glass, this is a typical mildly reductive wine; if they persist, the fault is more serious. Natural wines made with minimal sulphur addition are sometimes reductive.
Volatile Acidity (VA)
Volatile acidity, primarily acetic acid (vinegar), is produced by acetic acid bacteria when wine is exposed to oxygen during fermentation or ageing. A small amount of VA is normal and can add complexity; at higher levels it creates a sharp, vinegary character and can produce ethyl acetate (nail polish remover smell). VA is legally limited in finished wines and is considered a fault above threshold levels. High VA wines often smell prickly and sharp before they taste vinegary.
Key Vocabulary
Exam Question Examples
A wine smells of damp cardboard and mould. What fault is this and what causes it?
Approach
This is cork taint, caused by TCA (2,4,6-trichloroanisole). TCA is produced when naturally occurring fungi interact with chlorine compounds in cork. It creates musty, mouldy, wet cardboard aromas and suppresses fruit. The wine cannot be rectified.
How can you distinguish oxidation from deliberate oxidative ageing in a wine?
Approach
In a fault context, oxidation is unintentional and produces flat, stale, bruised apple aromas in a wine that should be fresh. Deliberately oxidised styles (fino vs oloroso Sherry, Tawny Port, Madeira) are made with controlled oxidation as a stylistic goal — they are complex, nutty, and intentional. Context (wine type, label) determines whether oxidation is a fault.
Quick Summary
- 1.Cork taint (TCA): damp cardboard/mould — caused by TCA in natural cork — cannot be fixed
- 2.Oxidation: flat, nutty, browning — too much oxygen — progressively worse over time
- 3.Reduction: rotten eggs, onion, struck match — too little oxygen — may improve with aeration
- 4.Volatile acidity: vinegar, nail polish — acetic acid bacteria — a fault above legal thresholds
- 5.Brett: farmyard, leather, band-aid — can be complexity or fault depending on level and context
Practice questions on this topic
Frequently Asked Questions
- Is brettanomyces always a fault?
- Not always. At low levels, Brett can add complexity and a savoury, earthy character that experienced tasters find appealing — it is part of the character of some traditional European reds. At higher levels it becomes overwhelming and unpleasant (strong farmyard, band-aid, manure). Whether it is a fault depends on the wine style, the producer's intentions, and the concentration.
- Can a reduced wine be fixed?
- Mild reduction can often be fixed by aerating the wine — vigorous decanting or swirling in the glass allows the volatile sulphur compounds to dissipate. If reduction aromas clear after 15–20 minutes in a glass or decanter, the wine is fine. Severe reduction that persists after aeration is a more serious fault.
Consolidate your knowledge
Use Vinlecta to practise exam-style questions on wine faults — identifying off-flavours and aromas and related topics under timed conditions.
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