You can detect signs of spoilage by paying close attention to the look and smell of the mushrooms. If you can detect an off odor, a difference in the appearance or flavor, or even mold — it is best to throw the mushrooms out. Don’t forget to also check the quality of the packaging of unopened canned mushrooms before use. If the packaging or tin displays any sign of damage, it needs to be disposed of. For example, if the tin leaks,  is bulging, dented, or rusting.