FSIS Logo Food Safety and Inspection Service
United States Department of Agriculture
Washington, D.C. 20250-3700
Consumer Education and Information
May 1997
Online Version Slightly Revised May 1998
Contact Information Slightly Revised May 2000

How Temperatures Affect Food

"Last night I left cooked roast beef on the counter to cool before refrigerating, but fell asleep and discovered it this morning. I immediately put it in the refrigerator. Since the meat is cooked, shouldn't it be safe to eat?"

The U.S.Department of Agriculture's Meat and Poultry Hotline receives similar calls every day from consumers who are confused about how to keep their food safe. The answer to this caller's question is that the roast beef should be thrown out. Why? Because leaving food out too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella enteriditis, Escherichia coli O157:H7, and Campylobacter) to grow to dangerous levels that can cause illness.

Bacteria exist everywhere in nature. They are in the soil, air, water and the foods we eat. When they have nutrients (food), moisture, time and favorable temperatures, they grow rapidly increasing in numbers to the point where some can cause illness. Therefore, understanding the important role temperature plays in keeping food safe is critical. If we know the temperature at which food has been handled, we can then answer the question, "Is it safe?".


Bacteria grow most rapidly in the range of temperatures between 40 and 140F, doubling in number in as little as 20 minutes. This range of temperatures is often called the DANGER ZONE. That's why the Meat and Poultry Hotline advises consumers to never leave food out of refrigeration over two hours. If the temperature is above 90F, food should not be left out more than one hour.


Raw meat and poultry should always be cooked to a safe internal temperature. Temperatures (160 to 212F) reached in baking, roasting, frying and boiling will destroy bacteria that can cause foodborne illness.

When roasting meat and poultry use an oven temperature no lower than 325F. Cook ground meats (beef,veal,lamb, and pork) to an internal temperature of 160F, and ground poultry to 165F. Steaks and roasts cooked to an internal temperature of 145F are medium rare, 160F are medium, and 170F are well done.

For doneness, poultry breast meat should be cooked to an internal temperature of 170F; 180F for whole birds. Use a meat thermometer to assure that meat and poultry have reached a safe internal temperature.

If raw meat and poultry have been handled safely, using the above preparation recommendations will make them safe to eat. If raw meats have been mishandled (left in the Danger Zone too long), bacteria may grow and produce toxins which can cause foodborne illness. Those toxins that are heat resistant are not destroyed by cooking. Therefore, even though cooked, meat and poultry mishandled in the raw state may not be safe to eat even after proper preparation.


One of the most common causes of foodborne illness is improper cooling of cooked foods. Because bacteria are everywhere, even after food is cooked to a safe internal temperature, they can be reintroduced to the food and then reproduce. For this reason leftovers must be put in shallow containers, for quick cooling and refrigerated within two hours.


Foods should be reheated thoroughly to an internal temperature of 165F or until hot and steaming. In the microwave oven, cover food and rotate so it heats evenly. Follow manufacturer's instructions for stand time for more thorough heating. In the absence of manufacturer's instructions, at least a two minute stand time should be allowed.


Properly handled food stored in a freezer at 0F will always be safe. Freezing keeps food safe by slowing the movement of molecules, causing bacteria to enter a dormant stage. Once thawed, these bacteria can again become active and multiply to levels that may lead to foodborne illness. Because bacteria on these foods will grow at about the same rate as they would on fresh food, thawed foods should be handled as any other perishable food.

A temperature of 40F should be maintained in the refrigerator. In contrast to freezer storage, perishable foods will gradually spoil in the refrigerator. Spoilage bacteria will make themselves known in a variety of ways. The food may develop an uncharacteristic odor, color and/or become sticky or slimy. Molds may also grow and become visible. Bacteria capable of causing foodborne illness either don't grow or grow very slowly at refrigerator temperatures. A refrigerator/freezer thermometer should always be used to verify that the temperature of the unit is correct.

Safe food-handling practices are a good defense against foodborne illness. Because we know how different temperatures affect the growth of bacteria in in our food, we can protect ourselves and our families from foodborne illnesses by proper handling, cooking and storing foods at safe temperatures.

For additional food safety information about meat, poultry or eggs, call the toll-free USDA Meat and Poultry Hotline at 1 (800) 535-4555; Washington DC (202) 720-3333. It is staffed by home economists, dietitians and food technologists from 10 a.m. to 4 p.m. Eastern time year round. An extensive selection of food safety recordings can be heard 24 hours a day using a touch-tone phone.

The media may call Bessie Berry, Manager, USDA Meat and Poultry Hotline, at (202) 720-5604.

Information is also available on the Internet from the USDA Food Safety and Inspection Service Home Page at http://www.fsis.usda.gov/.

May 1997


For Further Information Contact:
FSIS Food Safety Education Staff
Meat and Poultry Hotline:

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