How temperatures affect food safety

“Last night I left a cooked roast beef on the counter to cool before refrigerating it, but I overslept and discovered it this morning. I put it in the fridge right away. Since the meat is cooked, shouldn’t it be safe to eat?’

The USDA’s toll-free meat and poultry hotline at 888-674-6854 receives similar calls daily 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 away. Why? Because leaving food too long at room temperature can cause bacteria (such as Staphylococcus aureus, Salmonella Enteritidis, E. coli O157:H7 and Campylobacter) grow to dangerous levels that can cause disease.

Bacteria exist everywhere in nature. They are in the soil, air, water and food. When bacteria have nutrients (food), moisture, weather, and favorable temperatures, they multiply, increasing to the point where some can cause disease. Understanding the vital role that temperature plays in maintaining food safety is critical. By knowing the temperature at which the food was processed, we can answer the question “Is it safe?”

Courtesy of the USDA

The “Danger Zone” (40 degrees F to 140 degrees F)

Bacteria grow fastest at temperatures between 40 degrees F and 140 degrees F, doubling in number in just 20 minutes. This range of temperatures is often referred to as the “Danger Zone”. That’s why the Meat and Poultry Hotline advises consumers never to leave food out of the refrigerator for more than 2 hours. If the temperature is above 90 degrees F, food should not be left out for more than 1 hour.

If you are traveling with cold food, take a cooler with plenty of ice, frozen gel packs, or another source of cold. If cooking, use a hot campfire or portable stove. It’s hard to keep food warm without a heat source when you travel, so it’s best to cook food before you leave home, refrigerate it, and transport it 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 degrees F. Use a food thermometer to make sure the 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 degrees F as measured with a food thermometer before removing the meat from the heat source. For safety and quality, let meat rest for at least three minutes before cutting or eating. Due to personal preference, consumers may choose to cook the meat at higher temperatures.
  • Cook all raw ground beef, pork, lamb, and veal to an internal temperature of 160 degrees F as measured with a food thermometer.
  • Cook all poultry to a safe minimum internal temperature of 165 degrees F as measured with a food thermometer.

If raw meat and poultry have been handled safely, the above preparation recommendations will make them safe to eat. If raw meat has been improperly processed, left in the “Danger Zone” for too long, bacteria can grow and produce toxins that can cause foodborne illness. These toxins, which are resistant to heat, are not destroyed by cooking. Therefore, even when cooked, improperly processed raw meat and poultry may not be safe to eat even after proper preparation.

Storage of leftovers
One of the most common causes of foodborne illness is improperly refrigerating cooked foods. Because bacteria are everywhere, even after food is cooked to a safe internal temperature, they can be reintroduced into the food and then reproduce. For this reason, leftovers should be placed in shallow quick-cooling containers and chilled within 2 hours.

Foods should be thoroughly reheated to an internal temperature of 165 degrees F or until hot and steaming. In the microwave, cover the food and rotate it to heat evenly. Follow manufacturer’s instructions for dwell time for more thorough heating. Without the manufacturer’s instructions, at least two minutes of downtime should be allowed.

Cold storage temperatures
Properly processed food stored in a freezer at zero degrees F will be safe. Freezing keeps food safe by slowing the movement of molecules, causing bacteria to enter a dormant phase. Once thawed, these bacteria can become active and multiply to levels that can 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 like any other perishable food.

The refrigerator should be maintained at 40 degrees F or below. Unlike freezer storage, perishable foods will gradually spoil in the refrigerator. Spoilage bacteria will present themselves in a variety of ways. The food may acquire an unusual odor or become sticky or greasy. Molds can also grow and become visible. Many times, however, contaminated foods may not look, smell, or taste spoiled. Bacteria capable of causing foodborne illness either do not produce or grow very slowly at refrigerator temperatures. An appliance thermometer should always be used to check that the appliance temperature 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 illness by properly handling, cooking and storing food at safe temperatures.

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