Oxidation in Wine: When Air Helps or Hurts
Learn what oxidation means in wine, the difference between intentional oxidative winemaking and wine faults, and how to identify oxidized wines.
Oxidation occurs when wine is exposed to oxygen, altering its color and flavor. Controlled oxidation creates Sherry-like nutty flavors, while uncontrolled oxidation is a fault that makes wine taste flat and stale.
Oxidation is one of the most important chemical processes in wine, capable of both creating magnificent flavors and completely ruining a bottle. Understanding when oxidation is desirable and when it is a fault is a fundamental part of wine knowledge, and it affects how you store, serve, and evaluate every wine you encounter.
What Is Oxidation?
Oxidation is a chemical reaction that occurs when wine is exposed to oxygen. At the molecular level, oxygen interacts with various compounds in wine, including phenols, alcohols, and aldehydes, triggering changes in color, aroma, and flavor. In white wines, oxidation causes the color to darken from pale straw to amber or brown. In red wines, the bright ruby or purple hues shift toward brick, tawny, and eventually brown.
Aromatically, oxidation transforms fresh fruit characters into nutty, caramel, toffee, bruised apple, and dried fruit notes. In small doses, this can add complexity and interest. In excess, it strips a wine of its vitality and leaves it tasting flat, stale, and lifeless.
Every wine experiences some degree of oxidation from the moment the bottle is opened. This is why wine changes in the glass over the course of an evening, often opening up and improving at first as gentle aeration releases aromatic compounds, then gradually fading as extended oxygen exposure takes its toll.
Why Oxidation Matters
Understanding oxidation matters for two reasons. First, it helps you recognize and appreciate intentionally oxidative wine styles, some of the most distinctive and fascinating wines in the world. Second, it helps you identify and avoid faulty wines that have been damaged by unintended oxygen exposure.
Controlled oxidation is a deliberate winemaking technique used to create specific styles. Sherry from Spain is perhaps the most famous oxidative wine. Fino and Manzanilla Sherries are aged under a protective layer of yeast called flor, which shields them from oxygen, but Oloroso and Amontillado Sherries undergo extended oxidative aging in partially filled barrels, developing rich nutty, caramel, and toffee flavors. Madeira from Portugal takes oxidation even further, combining heat and oxygen exposure to create wines of extraordinary complexity and near-immortal longevity.
In France’s Jura region, Vin Jaune is aged for over six years in barrels that are intentionally not topped up, allowing a film of yeast to form and controlled oxidation to add distinctive walnut and curry-like notes. Orange wines, white wines made with extended skin contact, often have an oxidative character that adds a rich, amber color and savory depth.
Unintentional oxidation, however, is a common wine fault. It can occur when a cork fails and allows air to seep into the bottle, when a wine is stored upright for too long (drying out the cork), when a bottle is exposed to heat, or when wine is left open too long after serving. An oxidized white wine will appear brownish with muted aromas and a flat, lifeless palate. An oxidized red wine loses its vibrant fruit and develops an unappealing stale quality.
Oxidation in Practice
Winemakers protect wine from unwanted oxidation through several techniques. Sulfur dioxide, added in small amounts throughout the winemaking process, acts as an antioxidant, scavenging oxygen before it can damage the wine. Inert gas blanketing, using nitrogen or argon to fill the headspace in tanks and barrels, prevents oxygen from contacting the wine surface. Careful cellar hygiene, prompt topping up of barrels, and the use of quality closures all contribute to preventing premature oxidation.
The choice of bottle closure affects oxidation over time. Natural cork allows a tiny amount of oxygen exchange, which is beneficial for wines intended for long aging, as it contributes to slow, positive evolution. Screw caps provide a nearly airtight seal, preserving freshness but potentially limiting the positive oxidative development that some wines need. Synthetic corks fall somewhere between the two.
To identify oxidation when tasting, look for visual clues first. A white wine that appears darker or more golden than expected for its age may be showing signs of oxidation. On the nose, nutty, sherry-like, or bruised apple aromas in a wine not made in an oxidative style are red flags. On the palate, an oxidized wine tastes flat, dull, and lacking in fresh fruit character.
For wines you enjoy at home, minimizing oxidation after opening is important. Recork or reseal the bottle promptly, store it in the refrigerator (even reds benefit from cold storage once opened), and try to finish it within one to three days. Vacuum pumps and inert gas spray systems can extend this window by reducing the oxygen in the bottle.
Explore with Sommo
Learning to identify oxidation, whether intentional or faulty, is a critical tasting skill. Sommo’s structured tasting notes help you evaluate a wine’s condition and development, and our WSET study tools cover oxidative winemaking in depth, helping you appreciate styles like Sherry and Madeira while recognizing when something has gone wrong.
