If you're not sure if your walnuts have gone bad, there are a few things you can do to check. First, take a look at the color of the nut meat. If it's brown or black, that's a sign that the nuts are rancid. Another way to tell if walnuts have gone bad is by smelling them. Rancid nuts will have an unpleasant smell that is similar to paint fumes. Finally, try tasting the nutmeat. If it tastes bitter or sour, those are also signs that the nuts are no longer good to eat. If you notice any of these signs, it's best to throw out the walnuts and buy fresh ones.