When a bottle of wine has been opened the opened bottle of wine will last from 5 to 7 days in the refrigerator before it goes bad.
When wine has gone bad the smell of the wine will change and it may start growing mold inside the bottle of wine.
If the opened bottle of wine smells like musty basement, wet cardboard, or vinegar then the wine has gone bad and should be dumped out or it could make you sick.
If the wine changes to a brownish color or if the wine is red wine and tastes sweet then it has gone bad.
Also if the wine is not a sparkling wine and it tastes fizzy then the wine is bad and should not be consumed.
You will also notice a bad taste to the wine that may make you want to vomit so you'll usually detect the bad wine when you smell or taste it.
I've smelt bad wine before and it made my stomach hurt just smelling it.