Refermentation is a wine fault that occurs when residual sugar in a wine ferments again in the bottle. This can result in an increase in alcohol content, carbon dioxide production, and pressure inside the bottle. The wine may also develop off-flavors and aromas, such as yeasty or cidery notes.

Refermentation can be caused by a number of factors, including incomplete fermentation prior to bottling, the addition of sugar or unfermented grape juice to the wine, or contamination with yeast or bacteria.

To prevent refermentation, winemakers can stabilize the wine by filtering or adding sulfur dioxide. However, these methods can also affect the wine's flavor and aroma.

There are some styles of wine, such as sparkling wine, that intentionally undergo refermentation in the bottle. However, these wines are carefully monitored and controlled to ensure that the refermentation process produces the desired results without creating off-flavors or causing the bottle to explode.

If you suspect that a wine has undergone refermentation, you can look for signs such as a cork that extends beyond the lip of the bottle, a concave or convex indentation in the cork, or bubbles or sediment in the wine. However, the best way to avoid refermentation is to store wine in a cool, dark place and to consume it within a reasonable amount of time after purchase.

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