7 Slow Cooker Mistakes to Avoid, According to Chefs

The slow cooker is a staple tool in the home kitchen, especially if you have a big family or like to meal prep. It makes it possible (and safe!) to cook entire meals unattended, allowing you to free up other areas of the kitchen or tackle the day's to-do list. However, slow cooking isn't as simple as tossing in ingredients and pressing a button. There are important steps and techniques that are often overlooked, especially by those who are accustomed to stovetop or oven cooking. These errors can yield a watery and flavorless meal—but the good news is that they're easy to prevent.

We asked chefs and cooking teachers to explain what you should never do while slow cooking food, plus ways to avoid the most common slow cooker mistakes.

1. Adding Delicate Vegetables Too Early

Due to the slow cooker's lengthy cooking time, most vegetables will become overcooked and mushy if they're added too soon, says Stephen Chavez, chef instructor at the Institute of Culinary Education in Los Angeles. This is especially true of more delicate produce, such as zucchini or peas, says Isamar Leal, recipe developer and chef creative director at Florida Education Institute. Thus, if your recipe calls for these items, it’s best to add them at the end of the cooking process to preserve their texture and taste, she says.  

The exception? "If you plan to blend the ingredients, like in a [pureed] soup, it’s fine to add everything at the front end," says Chavez. Meanwhile, fibrous vegetables, such as onions and carrots, can be added early on as they'll hold their structure well. "But you must cut them into large pieces to ensure they maintain their shape," he says. It's also recommended to place these items on the bottom or near the sides of the slow cooker, as they take longer to cook than meat.

2. Overfilling the Slow Cooker

It can be tempting to fill a slow cooker to the top, especially if you’re preparing a big-batch recipe or cooking for a crowd. But this will technically overfill the slow cooker. "When a slow cooker is too full, it may not heat the food evenly," explains Leal. As a result, some parts of the dish may overcook, while others remain undercooked. "This can also increase the risk of foodborne illness, because the food might not reach a safe temperature throughout," she says.

What’s more, "overfilling your slow cooker could lead to food spilling over as it starts to warm, which would create a mess," says Traci Weintraub, chef and founder of Gracefully Fed, a restaurant in Los Angeles. "Ideally, you should only fill a slow cooker about three quarters full so there's room [for ingredients and liquid] to expand."

3. Using a Slow Cooker to Reheat Food

If you need to reheat leftovers, skip the slow cooker, per the USDA. "The 'slow' aspect of a slow cooker is what makes reheating food in [the appliance] problematic," says Weintraub. When food is cooked raw in a slow cooker, it takes a long time for the food to reach the minimal internal temperature of 165 degrees Fahrenheit. The slow cooker will also maintain this temperature for hours, which will kill any potentially harmful bacteria, explains Weintraub. In contrast, "if you’re reheating cooked food, it won’t take as long to get warm, [and] there may not be enough time for bacteria to be killed," she says.

A slow cooker can be used to keep hot food warm for serving, however. Simply bring the food to steaming on the stovetop or microwave, then place it in a preheated slow cooker, as instructed by the USDA. The food should stay at 140 degrees, which you can check using a food thermometer.

4. Not Reducing Liquid for Soups and Stews

When making a stovetop soup or stew recipe in a slow cooker, using the same amount of liquid can yield a watery, not-so-pleasant dish. "Because of the tight seal on slow cookers, steam and juices will accumulate as the food warms," says Weintraub. The liquids also won’t evaporate as much. To avoid excess liquid, reduce them by 10 to 20 percent to start, then adjust from there every time you make the recipe, says Weintraub. The Crockpot website also notes that most slow cooker recipes won't need more than 1/2 to 1 cup liquid, as slow cooking will preserve the natural juices in meats and vegetables.

If you've already slow cooked a dish and there's too much liquid, simply add cornstarch or tapioca starch, then cook for 15 minutes on high heat. You can also remove the meat and vegetables, then heat the liquid on the stovetop (sans lid) until it's thickened and reduced.

5. Not Searing Meat Before Putting It in a Slow Cooker

Another slow cooker mistake is failing to sear meat before adding it to the appliance. According to Crockpot, the extra step will pave the way for more even cooking. "Searing the meat allows for the Maillard reaction and caramelization on the surface of the meat [to take place], which provides more flavor [and] color," says Chavez. It also changes the texture of the meat's exterior, ensuring it holds up to slow cooking and doesn't disintegrate.  

6. Putting Frozen Foods in a Slow Cooker

Despite the long cooking time of a slow cooker, it's not the best appliance for cooking foods from frozen. According to Leal, directly adding frozen foods can significantly increase the time it takes for the appliance to reach a safe cooking temperature. As a result, it will stay in the temperature danger zone (between 40 and 140 degrees) for a longer time, allowing foodborne illness-causing bacteria to multiply and grow, she says. Frozen ingredients can also cool other items in the slow cooker, per the USDA. Therefore, it's recommended to thaw meat and poultry before adding it to the slow cooker.

7. Adding Fresh Herbs Too Early

Incorporating fresh herbs from the get-go is a mistake when it comes to slow cooking. "Much like vegetables, fresh herbs will overcook and lose their flavor if [cooked] too long," says Chavez. With that in mind, it’s best to add them at the very end of cooking or as a garnish.

Dried herbs, however, will fair well when added in the beginning. According to Weintraub, dried herbs can generally withstand the temperature and time in a slow cooker. The cooking process will also help dried herbs give flavor to the dish as they're rehydrated and heated, says Chavez.