For most people it’s hard to determine whether buttermilk has gone bad, or not. Buttermilk is a product spoiled intentionally, so it’s obviously difficult to tell if an already-spoiled product is fine, or not. There are, however, a few things that might indicate that buttermilk isn’t fit for consumption. If the product has very strong sour odor, or smells spoiled, it should be thrown out. If you can find any signs of mold, you should discard the buttermilk either. You should also check its consistency – if, after shaking the buttermilk, it’s still very thick than the product is probably not fit for consumption.