Some wine labels dictate that the wine is allowed to "breathe or aerate" before drinking. Breathing or aerating a wine may involve more than the removal of the cork as the wine may also be decanted to provide the full benefit of the process.
A general rule of thumb is to taste the wine as soon as it is opened to determine how long it may be aerated, if at all. The wine should then be tasted every 15 minutes until it is deemed ready to drink according to individual preference. Younger white wines normally require no more than 15-30 minutes of aeration while younger red wines should be no more than 30-60 minutes.
During aeration, the exposure of younger wines to air often "relaxes" the flavors and makes them taste smoother and better integrated in aroma, texture, and flavor. Wines that are older generally fade (lose their character and flavor intensity) with extended aeration. If in doubt, opt for too little aeration or breathing rather than too much.