What Is Oxidation in Wine?

The same process that browns an apple or rusts metal can also spoil your wine.
Yes, we are talking about oxidation!

Oxidation is a chemical reaction driven by the oxygen. When the wine is in contact with the air, some compounds, like ethanol, can be converted into acetaldehyde and, in some scenarios, even into acetic acid, one of the main components of vinegar.
In limited amount and controlled conditions, oxygen can enhance wine complexity, but, if in excess, it can compromise the final quality and its characteristics.

Oxidation will first impact on color, turning white wine into deeper yellow color or the reds into more brown and brick hue. It will then impact on the aroma and taste of a wine, converting the fresh and fruity aromas that will fade into more nutty and almondy aromas, or even into vinegar.
It affects also the aging capability, because it will limit the shelf life and reduce its stability over time.
However, proper oxygen management can enhance wine’s complexity, bringing in notes of dried fruits, spices and also caramel.
Winemakers can control oxidation by limiting the air exposure of the wine through the use of inert gases.
They can use sulfites to reduce and limit the oxygen reaction.
They can also control temperature and choose the right vessel during the aging process, because for example, stainless steel will limit the air exposure, while oak tanks would allow for controlled micro-oxygenation, like this.
At the end, they can ensure proper bottling conditions to limit the oxygen intake in the bottle.

However, there are exceptions to the rules, where some wines can develop a unique flavor from deliberate oxidation.
Think of Vin Jaune or the fortified wines Marsala, Porto and Madeira.
In conclusion, oxygen is a natural, nuanced, but double-edged process. With the right expertise, it can elevate a wine’s quality, but if unmanaged, it can compromise its final characteristics.