Certain manufacturers say their peanut butter powders are shelf-stable, whereas other manufacturers simply don’t mention it. Many powders are preservative-free, so they’ll spoil more quickly at room temperature. Even with shelf-stable peanut butter powders, some consumers report a rancid or sour smell if the jar is left in a cupboard or pantry. For best results, keep your peanut butter powder in the refrigerator with your other condiments.