What happens to wine when oxygen penetrates a natural cork in bottle of wine?

When oxygen penetrates a natural cork in a bottle of wine, a process called oxidation occurs. This is a complex chemical reaction that involves the interaction of wine components with oxygen, primarily the polyphenols in the wine.

Here's a breakdown of what happens:

1. Initial Stages:

* Color changes: The wine's color can become lighter, particularly in red wines.

* Aroma changes: The wine's aromas can become duller and less intense. Fruitiness and freshness are often lost, replaced by notes of "cooked" fruit, dried fruits, or even sherry-like qualities.

* Flavor changes: The wine's flavor can become flatter, less complex, and even bitter. The tannins may become more pronounced and harsh.

2. Long-Term Oxidation:

* Vinegar formation: If the wine is exposed to oxygen for a long time, it can become more acidic and develop a vinegar-like taste. This is due to the oxidation of alcohol to acetic acid.

Factors influencing oxidation:

* Cork Quality: A poorly-sealed cork will allow more oxygen to penetrate.

* Storage conditions: Wine stored in warm or humid conditions will oxidize faster.

* Wine Style: Red wines are generally more susceptible to oxidation than white wines.

* Wine Age: Older wines are generally more prone to oxidation.

Preventing oxidation:

* Choose good quality corks: Look for corks that are well-sealed and tightly fitted in the bottle.

* Store wine properly: Store wine in a cool, dark, and humidity-controlled environment.

* Minimize exposure to air: Once opened, transfer the wine to a smaller container or use a vacuum stopper to reduce air contact.

Note: Oxidation is not always a negative thing. Some wine styles, such as Sherry and Madeira, are intentionally oxidized as part of their production process.

In general, however, the goal of wine storage is to minimize oxidation in order to preserve the wine's freshness, aromas, and flavors.