Bacteria grow most rapidly in the range of temperatures between 40°F and 140°F
According to the U.S. Department of Agriculture:
Some bacteria can double their numbers within minutes and form toxins that cause illness within hours. Leaving food out too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella Enteritidis, Escherichia coli O157:H7, and Campylobacter) to grow to dangerous levels that can cause illness. Bacteria grow most rapidly in the range of temperatures between 40°F and 140°F, doubling in number in as little as 20 minutes. This range of temperatures is often called the “Danger Zone.”
Keeping Food out of the “Danger Zone”
Never leave food out of refrigeration over 2 hours. If the temperature is above 90 °F, food should not be left out more than 1 hour.
Keep hot food hot — at or above 140°F. Place cooked food in chafing dishes, preheated steam tables, warming trays, and/or slow cookers.
Keep cold food cold — at or below 40°F. Place food in containers on ice.