why do wine turn brown
The Short AnswerWine turns brown primarily due to oxidation, a chemical reaction where oxygen interacts with phenolic compounds in the wine. This process alters the wine's color pigments, leading to a duller, brownish hue and changes in its aroma and flavor profile. It is often a sign of spoilage in red wines and a natural part of aging for many white wines, though some styles embrace it.
The Deep Dive
The browning of wine is a complex chemical transformation driven mainly by oxidation. Wine contains various phenolic compounds, including anthocyanins, which are responsible for red color, and tannins. When wine is exposed to oxygen, enzymes like polyphenol oxidase (PPO) or non-enzymatic oxidation reactions initiate a cascade. Oxygen reacts with these phenolic compounds, forming highly reactive molecules called quinones. These quinones readily polymerize, or join together, with other phenolic compounds, creating larger, more stable brown-colored polymers. In red wines, this process can degrade the vibrant red anthocyanins, causing them to lose their color and form brown pigments. In white wines, clear phenolic compounds oxidize to golden, then amber, and eventually brown hues. Factors like temperature, light exposure, and the wine's pH also influence the rate of these oxidative reactions. The presence of sulfur dioxide (SO2) acts as an antioxidant, inhibiting these browning reactions, which is why winemakers carefully manage its levels. Over time, even without direct oxygen exposure, very slow oxidation through the cork can occur, contributing to the natural aging process and color evolution in some wines. However, rapid or excessive oxidation is generally detrimental, leading to a "sherried" or oxidized taste that is often undesirable.
Why It Matters
Understanding why wine turns brown is crucial for winemakers, distributors, and consumers alike. For winemakers, it informs critical decisions regarding oxygen management during production, aging, and bottling to preserve desired color and flavor profiles, preventing spoilage and maintaining product quality. Consumers benefit by recognizing signs of oxidation, which can indicate a faulty bottle, saving them from an unpleasant experience. This knowledge also enhances appreciation for the subtle art of winemaking, highlighting the delicate balance between oxygen's role in beneficial aging and its potential for detrimental spoilage. It explains why some wines are meant to be consumed young, while others develop beautifully with controlled oxidation over decades, showcasing diverse styles.
Common Misconceptions
A common misconception is that all browning in wine indicates spoilage. While rapid or excessive browning often signifies a faulty wine, some white wines, like certain aged Rieslings or Sauternes, naturally develop a golden to amber hue with age, which is desirable and part of their complex character and flavor development. Another myth is that simply recorking an opened bottle completely stops oxidation. While it slows the process, oxygen already dissolved in the wine continues to react, and the small amount of air trapped above the wine will continue to cause browning and flavor changes. Specialized stoppers that remove air or inert gas preservation are more effective at significantly slowing down this process after opening.
Fun Facts
- The browning process in wine is chemically similar to how a cut apple turns brown when exposed to air.
- Winemakers sometimes intentionally expose certain wines, like Sherry, to controlled oxidation during aging to develop specific nutty and complex flavors.