Our editors review and recommend products to help you buy the stuff you need. If you make a purchase by clicking one of our links, we may earn a small share of the revenue. Our picks and opinions are independent from any business incentives.

We tend to think of a refrigerator as a magic box that keeps beer cold and vegetables nice and crisp. But we don’t usually think about the real job of the fridge—keeping food at the appropriate temperature to inhibit spoilage.

According to the CDC and FDA, your refrigerator should never be higher than 40ºF. If it does creep higher, bacteria can multiply rapidly, putting you at risk for food-borne illness. That's likely what happened at Chipotle this week, when 650 customers in Ohio became ill after eating at one of its locations. According to results returned by the CDC, those ill tested positive for Clostridium perfringens, a food-borne disease that occurs when food is left at an unsafe temperature. While the exact culprit isn't yet public knowledge, health inspectors specifically cited the store's lettuce and beans as being held at unsafe temperatures.

Unfortunately, this can happen in your own home, too. To prevent food-borne illness, in part, you'll need to keep your fridge at a safe temperature. But how do you know how cold your refrigerator actually is? Even if you have a newer fridge, the digital display on the front panel may not be accurate. Here's how to make sure your fridge stays cool enough to keep bacteria away from your food—and your family safe.

How cold should your fridge be?

Credit: Reviewed.com
Some refrigerators have a dial to allow you to adjust the temperature. Make a change if necessary once you've tested with a thermometer.

To keep food out of what the USDA calls "the danger zone", it needs to remain below 40°F. The freezer should to be 0°F to keep freezer burn at bay. If your fridge and freezer are regularly warmer than those temperatures, you’re risking faster spoilage.

Here at Reviewed, we’ve tested more than 200 refrigerators to find out which ones do the best job keeping your food safe. When we run our tests, we’re not only looking for a refrigerator to reach an appropriate temperature—which will take 24 hours or more—we’re also looking for its ability to remain at the right temperature.

Temperatures always vary somewhat, because of the way a refrigerator works. The motor is not always running, and defrost cycles bring the temperature up. But if the temperature extremes are excessive, food in the fridge may not always be cold enough to stay fresh, and food in the freezer may be vulnerable to freezer burn.

How you can test your fridge's temperature

Credit: Reviewed.com
Use a refrigerator thermometer to determine how cold it is inside your refrigerator. Placing the thermometer in a glass of water is a good idea, because it will measure the temperature inside your food, as opposed to the temperature of the air in the fridge.

To ensure that your refrigerator is running at the right temperature, we recommend that you purchase a refrigerator thermometer. It’s a small investment, and although it's not quite as accurate as the thermocouples we use in our labs, it's close enough and can save you from a nasty stomach bug.

To use, place the thermometer in a cup of water. Why? Your refrigerator measures the temperature of the air around your food, but you want to simulate the temperature inside your foods. Check the thermometer after 24 hours in both the fridge and the freezer. Then, adjust the temperature of each appliance, based on the results.

Next, use the thermometer to find out where the cold spots are in the refrigerator and freezer by repeating the test in separate corners and the door. Although there may be dedicated space in the door for a gallon of milk, the door is the warmest spot in your fridge, and milk won’t stay as fresh as long there as it would on a shelf toward the back.

Tips for keeping a cool fridge

Credit: Getty Images

Once you’ve set your refrigerator to the right temperature, here are a few tips for keeping it there.

  • Don’t open the door more often than necessary. As a mom, I know this is a losing battle.

  • Don't open the fridge during a power failure, if you can help it. Every freezer we’ve ever tested will hold a safe temperature for 36 hours as long as you don’t open the door.

  • Check to make sure the gasket is in good shape, and seals well. If you can open the door with one finger, your seal isn't tight enough. A leaky seal is an energy waster, and may be a risk to your food.

  • Dust your refrigerator's cooling coils, if they're visible. You can use a long, skinny brush made for this purpose.

  • Cover your food. For example, leave eggs in their carton, not in the door.

  • Keep a full fridge to retain the cold, but leave enough room for air to circulate.

For more details, read about how to make your refrigerator run more efficiently. And to find out more about storing food safely, check out the U.S. Food and Drug Administration website.