Chow Line: Assure food safety when using slow cooker


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I use my slow cooker a lot, but I recently read that you should thaw frozen items beforehand. I can understand that this would be necessary for meat, but is it a problem to use a bag of frozen vegetables without thawing it first?

That should be OK.

The idea behind thawing food before putting it into a slow cooker is to reduce the amount of time the food is in the “danger zone,” which is between 40 and 140 degrees F. That’s when any bacteria that might be on or in the food could multiply quickly and become a food safety concern. Food should move through the danger zone within two hours.

Meat is more dense than vegetables are, and if you put it in a slow cooker when it’s still frozen, it could stay in that danger zone for too long. Vegetables thaw more quickly, so it’s less of a concern to use frozen vegetables in a slow cooker.

Food safety is especially important to take into account if the food will be eaten by people most at risk from foodborne illness: older adults, children, pregnant women, or anyone undergoing cancer treatment or dealing with a chronic illness, such as diabetes. They are most at risk for developing serious complications from the intestinal problems that could result from food bugs.

Although slow cookers use low temperatures — generally between 170 degrees and 280 degrees F — to cook food, the lengthy cooking time and steam produced in the cooker combine to destroy bacteria. That said, it’s especially important to use some type of liquid (to generate steam) and to keep the lid on the slow cooker as much as possible during cooking. The temperature can dip 10 to 15 degrees F when the lid is removed.

To assure safety when using the slow cooker:

  • If you’re planning to cook a roast or other large cut of meat or poultry in the slow cooker, consult the manufacturer’s recommendations to be sure the meat is heated thoroughly quickly enough. Or, just cut the meat into smaller chunks first.
  • For the first hour, use the high setting. That will move the food through the danger zone more quickly. After that, you can switch to a lower setting if the food will be cooked all day.
  • You may want to test the heating capacity of your slow cooker. To do that, fill the crock in the slow cooker one-half to two-thirds full of water. Put on the lid and turn the heat to low, or 200 degrees F if you have a model with a temperature display. After eight hours, check the temperature of the water with a meat thermometer. Be sure to do so quickly, as the water will cool significantly as soon as the lid is removed. The water should be 185 degrees. If the temperature is below that, the slow cooker may be unsafe to use.

If you’re not home during the entire cooking process and the power goes out, throw away the food even if it looks done.

For more information about slow cooker food safety, see the U.S. Department of Agriculture’s fact sheet at

Chow Line is a service of Ohio State University’s College of Food, Agricultural, and Environmental Sciences and its outreach and research arms, Ohio State University Extension and the Ohio Agricultural Research and Development Center. Send questions to Chow Line, c/o Martha Filipic, 2021 Coffey Road, Columbus, OH 43210-1043, or

Editor: This column was reviewed by Linnette Goard, Food Safety, Selection and Management field specialist for Ohio State University Extension, the outreach arm of Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

For a PDF of this column, please click here.

Cooking won’t cure all food safety ills

I was making soup in the slow cooker but forgot to plug it in. After five hours, I realized what happened and cooked the soup, which included cooked chicken, on high for five more hours. I thought it would be OK, but my wife said no and threw it out. Who was right?

She did the right thing by throwing away the soup.

One of the basic rules of food safety is that perishable foods should be kept at room temperature — well, actually, anywhere between 40 degrees F and 140 degrees F — for no more than two hours. Any longer than that, and you’re taking too big of a chance that any bacteria or other pathogens will multiply so much that they could make you sick.

At room temperature, bacteria in food can double every 20 minutes. That means that a mere five cells of bacteria can multiply to 320 cells in two hours, or to 163,840 cells in five hours. The more bacteria there are, the greater the chance of illness.

In fact, experts recommend that food be refrigerated within one hour, not two, if the temperature outside is above 90 degrees F, because the risk is just too great that bacteria could multiply even more quickly.

It’s true that if you cook food thoroughly even after allowing it to sit out, bacteria will be killed. But some types of pathogens that cause food-borne illness produce spores or toxins that are not eliminated by cooking. For example, a few types of E. coli bacteria produce something called Shiga toxin, which can cause a serious illness that can lead to renal failure.

Similarly, a bacterium called Clostridium perfringens produces tiny spores that can turn into full-fledged bacteria after cooking. With this bacteria, it’s especially important to refrigerate food within two hours after cooking. Refrigeration does a great job at slowing down bacteria’s multiplication process — so much that it greatly reduces the chance this bacteria will cause illness. But it’s important to note that refrigeration only slows down the process — it doesn’t destroy the bacteria.

Some other temperature-related food safety tips include:

  • When refrigerating large amounts of leftovers, use shallow containers to allow the food to cool more quickly.
  • Don’t thaw frozen food at room temperature. It’s always best to thaw food in the refrigerator. Other, quicker options are to use the defrost setting in the microwave oven, or use cold water (lower than 70 degrees F) to thaw the food. If you try the latter, be sure the food is wrapped in a leak-proof package, and change the water every 30 minutes.

For more information, see