Take a big gulp and if you puke your guts out it is a very good indication that it is bad. lolBut seriously, you can tell it has gone bad by the smell. Its called oxidation. If you have a clear bottle, look for coloring, or mold. If the cork was once removed, the **** must be drunk within the same day. So if you have old dusty bottles like this, I would just trash them.For good **** deals, go here: tinyurl. com/2yjm4elc