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 Enteritidis, 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 bacteria have nutrients (food), moisture, time and favorable temperatures, they grow rapidly, increasing in numbers to the point where some can cause illness. 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?"
The "Danger Zone" (40 °F-140 °F)
Bacteria grow most rapidly in the range of temperatures between 40 ° and 140 °F, 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 2 hours. If the temperature is above 90 °F, food should not be left out more than 1 hour.
If you are traveling with cold food, bring a cooler packed with plenty of ice, frozen gel packs or another cold source. If you are cooking, use a hot campfire or portable stove. It is difficult to keep foods hot without a heat source when traveling, so it's best to cook foods before leaving home, cool them, and transport them cold.
Raw meat and poultry should always be cooked to a safe minimum internal temperature. When roasting meat and poultry, use an oven temperature no lower than 325 °F. Use a food thermometer to assure that meat and poultry have reached a safe minimum internal temperature.
- Cook all raw beef, pork, lamb and veal steaks, chops, and roasts to a minimum internal temperature of 145 °F as measured with a food thermometer before removing meat from the heat source. For safety and quality, allow meat to rest for at least three minutes before carving or consuming. For reasons of personal preference, consumers may choose to cook meat to higher temperatures.
- Cook all raw ground beef, pork, lamb, and veal to an internal temperature of 160 °F as measured with a food thermometer.
- Cook all poultry to a safe minimum internal temperature of 165 °F as measured with a food thermometer.
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 2 hours.
Foods should be reheated thoroughly to an internal temperature of 165 °F 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.
Cold Storage Temperatures
Properly handled food stored in a freezer at 0 °F will 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 40 °F 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. An appliance 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 our food, we can protect ourselves and our families from foodborne illnesses by properly handling, cooking and storing foods at safe temperatures.