No, it's not forgetting to unplug it (though you should do that, too).
Slow cookers are beloved for their set-it-and-forget-it style. The best slow cooker recipes require very little hands-on time, and make the machine do all the heavy lifting. Naturally, most of us don’t think twice when a recipe tells us to start with frozen chicken. After all, that’s the point—to let the slow cooker do the work of thawing and cooking the meat. Right?
Not so fast, says the USDA. According to their Slow Cookers and Food Safety guidelines, you should always thaw meat or poultry before putting it in a slow cooker. They recommend storing the thawed meat in the refrigerator before adding it in. “The slow cooker may take several hours to reach a safe, bacteria-killing temperature,” the guidelines read. “Constant refrigeration assures that bacteria, which multiply rapidly at room temperature, won’t get a ‘head start’ during the first few hours of cooking.”
The primary concern is that putting frozen meat in the slow cooker increases its chances of entering the “danger zone,” the temperature range between 40° and 140°F where harmful bacteria grow exponentially. Slow cookers operate at temperatures between 170°F and 300°F—well above this zone—but it takes longer for frozen meat or poultry to reach those temperatures than thawed meat, giving it more opportunity to sit in the danger zone.
Here’s where things get a little murky. The guidelines for the Instant Pot, which can function as a slow cooker, say there’s “no need to defrost the food in the microwave prior to preparing.” They recommend increasing the cook time if beginning with frozen food, but do not address any potential hazards. This is perfectly fine advice if using the pressure-cooker function, because a pressure cooker can cook frozen chicken or meat fast enough to avoid the “danger zone.” But the Instant Pot’s website doesn’t specify which function the guidelines are referencing.
Crock Pot, one of the most popular brands of slow cookers, also gives a thumbs up to the practice. “You can cook frozen meat in a Crock-Pot Slow Cooker, but suggested cook time may need to be increased.” They recommend using a meat thermometer to ensure meat is well above 165°F. What they fail to address is the time it takes to reach that temperature.
Today Food took a deep dive into the topic and found that food experts have differing options. Ultimately, they recommend following the USDA guidelines to help reduce the possibility of the development of harmful bacteria. And, because it’s better to be safe than sorry, we agree. Additionally, if you’re gone during the day while your slow cooker is on, it’s a good idea to cook on low rather than set the timer to shut it down in the early afternoon. Food shouldn’t sit in a turned-off slow cooker for more than four hours, or it runs the risk of entering the danger zone again.