noun From oxidise (Greek oxys, "sharp/acid" + French oxygène) — the chemical reaction of a substance with oxygen

Oxidation /ˌɒksɪˈdeɪʃən/

In wine, the chemical reaction of wine compounds with oxygen, which alters colour, aroma and flavour. Oxidation can be a winemaking fault (unintended premature oxidation), a deliberate stylistic choice (sherry-style wines), or the natural process that occurs when a bottle is opened.

Four types of oxidation in wine

Unintentional / fault

Aroma Flat, stale, bruised apple (white wine); cooked or dried fruit, loss of freshness (red wine)

Cause Faulty closure, poor storage, excessive oxygen exposure during transport or winemaking

Outcome A flaw — the wine has been damaged and cannot be restored. Discard or return.

Deliberate / winemaking technique

Aroma Walnut, hazelnut, almonds, dried fruit, toffee, marzipan

Cause Intentional oxygen exposure: Sherry solera ageing, Tawny Port barrel maturation, Jura vin jaune under voile

Outcome A defining stylistic feature — the wine is designed to taste this way. Not a fault.

Micro-oxygenation

Aroma Softer tannin, rounder mouthfeel; accelerated integration

Cause Controlled tiny amounts of oxygen introduced during ageing, mimicking slow barrel ageing. Common in New World red production.

Outcome A tool — can be positive (tannin softening) or overused (flat, prematurely aged character).

Post-opening

Aroma Variable: initial "opening up" of aromas, then progressive flattening and staling

Cause Normal exposure to air after the bottle is opened. Begins immediately; significant after 24–72 hours.

Outcome Natural and inevitable. Managed by refrigeration, wine preservers and finishing the bottle.

The chemistry of oxidation in wine

Wine is primarily water and ethanol, but also contains hundreds of minor compounds including phenolics, pigments, acids and aromatic esters. Oxygen reacts with these compounds at different rates. Ethanol itself oxidises slowly to acetaldehyde (which smells of bruised apple and is the primary "flat" note in oxidised white wine). Pigments (anthocyanins in red wine) oxidise and polymerise, causing colour to fade from ruby to orange-brown. The volatile compounds responsible for fresh fruit aromas are among the first casualties of oxidation.

Sulphur dioxide (SO₂) prevents this by acting as a sacrificial antioxidant — it reacts with oxygen first, before oxygen can attack the wine's flavour compounds. This is why the sulphite debate in natural wine is partly about oxidation risk: removing sulphites removes the primary antioxidant protection. For how to protect wine after opening, see the How long an open bottle lasts guide.

Wine oxidation, wine faults and wine taints

Wine oxidation is the most common wine fault encountered by consumers — it occurs when oxygen reacts with the wine's flavour compounds, producing flat, stale, bruised-apple aromas and causing colour changes (whites turn amber-brown; reds lose vibrancy and shift toward orange-brown). An oxidised wine has lost its freshness irreversibly. Oxidation is one of several recognised wine faults and wine taints that affect the drinking experience. Other faults include cork taint (TCA contamination — damp cardboard, wet dog aroma), volatile acidity (vinegar, nail polish remover), reduction (rotten eggs, struck match), and heat damage (cooked, jammy character). Wine taints differ from faults: taints are contamination from external sources (smoke taint from wildfires, chemical contamination from storage environments), while faults arise from the winemaking or storage process itself. The WSET Level 2 and above curricula cover fault identification systematically, and Decanter publishes a comprehensive wine fault identification guide.

Sources: OIV (oiv.int) — wine chemistry standards. WSET (wine oxidation and fault identification curricula). Sulphite and antioxidant chemistry: AWRI. Closure technology: Amorim Cork and Diam Closures (TCA-free cork technology).

Questions

About oxidation in wine.

What does oxidation smell like in a wine that has gone off?

In white wine: flat, stale, like a bruised apple or wet cardboard mixed with honey. The fresh citrus and fruit aromas disappear; what remains is dull and lifeless. In red wine: the fresh berry fruit fades and is replaced by dried fruit, stewed prum or raisin character, with a general flatness. In both cases, the wine lacks the vitality and freshness it should have. This is the most common fault in wines that have been left open too long or stored poorly. See the Common wine faults guide for a full fault identification reference.

Why do some wines intentionally taste oxidised?

Certain wine styles are deliberately made through controlled oxidation, developing a completely different — and intentionally sought — flavour profile. Fino and Manzanilla Sherry age under a protective layer of yeast (flor) with limited oxygen but some exposure; Oloroso Sherry ages with direct, extended oxidative barrel contact. Tawny Port ages in small barrels, gaining oxygen slowly over decades. Vin Jaune from the Jura region of France ages under a veil of yeast. These styles taste of walnuts, hazelnuts, dried fruit, toffee and spice — flavours that are the result of intentional oxidation. See the fortified wine methods guide for how Sherry and Port ageing works.

How do sulphites prevent oxidation?

Sulphur dioxide (SO₂) acts as an antioxidant: it reacts preferentially with oxygen before oxygen can react with the wine's flavour and colour compounds. Winemakers use sulphites at key risk points — after pressing, before fermentation, after fermentation, at bottling — to protect against oxidation. The antioxidant effect is one of two primary roles of sulphites (the other is antimicrobial). Wines without added sulphites (natural wines) are more vulnerable to oxidation and require alternative protective strategies: inert gas blanketing, cool temperatures, rapid bottling. See the natural wine and sulphites article for the full discussion.

Does decanting accelerate oxidation?

Yes — decanting exposes wine to significant oxygen, which is exactly the point for young, tannic reds: the controlled oxidation softens tannins and opens up aromas. However, delicate older wines are more fragile: their aromas are easily stripped by too much oxygen exposure, and they decline more quickly once decanted. This is why old Burgundy, aged Barolo and vintage Champagne should be decanted briefly (or not at all) rather than left in a wide-bottomed decanter for hours. See the decanting explained guide for timing by wine style.

Does wine go bad? How can you tell?

Yes, wine can go bad, and there are several distinct ways this happens. Oxidation (the most common): the wine smells flat, stale, like bruised apple or dried fruit — it has lost its freshness. Cork taint (TCA): damp cardboard, mouldy cloth. Volatile acidity: vinegar, nail polish remover. Heat damage: stewed fruit, jammy, overripe — the wine has been cooked inside the bottle by heat exposure. All of these faults are harmless (the wine is not dangerous to drink) but unpleasant. Wine that has "gone bad" is not contaminated in a way that poses health risks — it simply tastes poor. See the Common wine faults guide for a full reference with symptoms and causes.

How can I tell if a wine is oxidised or has a wine taint?

An oxidised wine shows these signs: white wine turns amber or dark gold (beyond what age would explain), smells of bruised apple, stale honey or wet cardboard, and tastes flat with no freshness. Red wine loses its vibrant colour (shifting toward brown-orange), smells of dried-out fruit, stewed prunes or vinegar, and tastes lifeless. Other wine faults and wine taints have distinct signatures: cork taint (TCA) smells of damp cardboard or mouldy newspaper — even in tiny concentrations it strips fruit aromas. Volatile acidity (VA) smells of vinegar or nail polish remover. Reduction smells of rotten eggs, struck match or rubber. Heat damage ("cooked wine") shows jammy, baked or stewed fruit with a flat palate. Smoke taint gives an ashy, campfire character. None of these faults are harmful to health — they simply make the wine unpleasant to drink. If you suspect a wine is faulty, any reputable wine shop or restaurant will accept a return. See the common wine faults guide for the full reference.

What is "premature oxidation" (premox)?

Premature oxidation (premox) describes white wine — particularly white Burgundy and Champagne — that develops oxidative characteristics far earlier than expected, typically within 3–7 years of bottling rather than the 10–20 expected. The wine shows flat, nutty, stale notes where it should be fresh and vibrant. The cause was debated for years but is now linked mainly to cork quality, fill levels and bottling oxygen exposure. Burgundy producers moved to tighter quality control of corks and bottling lines in the 2010s following widespread premox reports in 2000s vintages. It is less common in recent releases.