Final answer:
Food must be cooled from 135F (57C) to 70F (21C) within 2 hours to prevent bacterial growth and ensure food safety.
Step-by-step explanation:
According to food safety guidelines, food must be cooled from 135F (57C) to 70F (21C) within 2 hours. This is to ensure that perishable foods are kept out of the temperature danger zone, which is between 40F (4C) and 140F (60C), where bacteria can multiply rapidly and cause foodborne illnesses. Rapid cooling helps to prevent bacterial growth and maintain the quality and safety of food.