Clostridium botulinum bacteria can grow in food in the absence of oxygen and produce the deadly botulinum toxin, so sous vide cooking must be performed under carefully controlled conditions to avoid botulism poisoning.[12] Generally speaking, food that is heated and served within four hours is considered safe, but meat that is cooked for longer to tenderize must reach a temperature of at least 55 °C (131 °F) within four hours and then be kept there for sufficient time, in order to pasteurize the meat.