Browning in red wine

Oxidation and reduction in red wines can lead to a particularly undesirable brick red color in red wines (or an "orangey" color in white wines). This process is sometimes referred to as browning. In chemical terms, this is called a redox reaction because first the color of the wine deepens after fermentation through oxidation, and then the color begins to brown after bottling through reduction. Browning is not strictly considered a bad thing in every wine that is produced, as sometimes the oxidation process can contribute to the style of the wine in a positive and desirable way.

Generally speaking, however, browning is a sign of the wine going stale from too much exposure to oxygen. Although wine that has gone bad is typically associated with the smell and taste of vinegar or unwanted effervescence, oxidation itself can actually lead to "nutty", "applesauce", and "burnt marshmallow" aromas. The sharp vinegar component comes from acetic acid formed through bacterial processes. A lower pH level is typically preferred in wines because it decreases the overall risk of spoilage. The lower pH reduces the effect of browning and yields better colors, particularly in red wines.