Can sherry wine that has been opened for years turn poison?

It's unlikely that opened sherry wine will turn poison in the literal sense. However, it will deteriorate over time and become unpalatable.

Here's what happens:

* Oxidation: Sherry, like most wines, is susceptible to oxidation when exposed to air. This process changes the chemical composition, leading to a loss of flavor and aroma.

* Evaporation: Sherry, especially the sweeter varieties, is prone to evaporation. This leaves behind a more concentrated, syrupy liquid that may taste overly sweet or cloying.

* Acetification: In some cases, the open sherry might undergo a process called acetification, where the alcohol is converted to acetic acid. This results in a vinegary taste and smell, rendering the wine undrinkable.

While not poisonous, aged open sherry will be:

* Unpleasant to taste: It will have lost its original flavor and aroma profile, becoming flat and stale.

* Possibly unpleasant to smell: The smell might become vinegary or overly sweet, depending on the type of sherry and the length of storage.

Here are some tips to extend the lifespan of open sherry:

* Store it properly: Keep the bottle tightly sealed in a cool, dark place, ideally in a wine cellar or refrigerator.

* Transfer to a smaller bottle: Once the bottle is opened, transfer the remaining sherry to a smaller bottle to minimize air exposure.

* Consider using a vacuum stopper: Vacuum stoppers help remove excess air from the bottle, slowing down oxidation.

Ultimately, the shelf life of open sherry depends on its type, storage conditions, and your personal tolerance for taste changes. If you're unsure about its quality, it's best to err on the side of caution and discard it.