Definition - What does Oxidation mean?
In the context of wine making, a wine becomes oxidized as the result of oxidation, a physical process between wine and oxygen that occurs when the oxygen is dissolved into the wine. Typically, characteristics of oxidation indicate improper wine making techniques or improper wine storage or aging. Oxidation can be done purposefully to create specific color and flavor charecteristics in wine such as port or madeira, however oxidation usually causes adverse effects including; loss of color, flavor and aroma.
WineFrog explains Oxidation
When wines are made there is a natural exposure to oxygen that can enhance the wine making process, oxidation occurs when the wine has been exposed to oxygen and the oxygen has dissolved into the wine. When wine makers make wine styles like port or madeira, they purposefully introduce oxygen into the winemaking process to develop specific characteristics in the wines, for example, in port and madeira, oxidation softens the colors and produces a smooth nutty flavor.
Oxidation occurs as a physical process when oxygen reacts with the phenolic compounds in the wine and causes them to oxidize; this creates another reaction with the polyphenol oxidase enzyme (but can also occur if this enzyme is not present). If left unchecked, oxidation will result in the loss of the vibrant color of the wine, as well as loss of flavors and aromas along with a nutty flavor that is brought about by the development of aldehydic as a result of the reaction of the oxygen and wine compounds.