If you didn’t know by now, yogurt does go bad. There are many ways to find out if yogurt has spoiled.  The first thing you should do is to carefully search for any discolorations or signs of mold on the surface of the yogurt. If you can find any, the product is spoiled and you should throw it out. Another good thing to do is to smell the yogurt. If it has any kind of odd, spoiled odor, discard it.  You can also check if it has gone bad by tasting it, if the yogurt is sour or just tastes awful, that’s a pretty obvious sign of spoilage.