And potatoes are very tricky—if they’re left to cool down at room temperature (after cooking them) instead of immediately refrigerating, the warm temperatures can promote the growth of botulism, a rare bacterium. Botulism can’t be killed with a quick zap in the microwave, so it’s best to refrigerate them immediately to avoid any problems with reheating. On the other hand, if you intend to eat your potato stew for a couple of days, take the potatoes out and just add them subsequently.