This isn't an issue that I have often, but sometimes I have left over wine that has been opened and not enjoyed within 3-5 days. What happens to the wine? I know that it oxidizes, but I don't really understand what that means. Young red wines improve with a few hours of oxidation right? When does this process switch from being a beneficial process to one that ruins the flavor? What I am really wondering about is if I can cook with say a half bottle of red that has been opened for about 2 weeks? I should clarify that I almost always use a vacuum pump (or at least re-cork) and do not refrigerate the left overs. I have tasted wine like this and it does not taste very good, almost sour. When I cook with wine I generally follow the 'if you wouldn't drink it, don't cook with it' rule. But I know that cooking wine drastically changes its qualities. I am wondering if the changes that occur during cooking counteract or at least mute the changes that happened from being opened too long. I might just have to do some experiments, but if anyone has any knowledge in this area it might save me some money and spare the world a wasted bottle of wine. Thank you.