UPDATE, AUGUST 2021
We have used almost a dozen units of our winning slow cooker, the KitchenAid 6-Quart Slow Cooker with Solid Glass Lid, in the test kitchen since our last review was published, and have found that they consistently work well. Having received some complaints about this winning slow cooker, we decided to retest it. We still find the KitchenAid 6-Quart Slow Cooker with Solid Glass Lid to be the best slow cooker for most people—both of the new units performed admirably in every test we ran. If you have any mechanical failures with your slow cooker, we recommend contacting the manufacturer's customer service (or that of the retailer from which you bought your unit).
Cook three recipes with varied requirements for time, temperature, and type of food: boneless, skinless chicken breasts in Thai Chicken with Coconut Curry Sauce (1 to 2 hours on low); whole bone-in Turkey Breast with Cherry-Orange Sauce (5 to 6 hours on low); and Classic Pot Roast (6 to 7 hours on high)
Heat 4 quarts water for 12 hours on low and 6 hours on high, tracking water temperature to map heating patterns and test maximum cooking temperatures
Disassemble set of cookers to examine construction and heating elements
Wash crocks and lids six times by hand and 10 times in dishwasher (for all dishwasher-safe models)
Have seven people of varying sizes and levels of experience with slow cookers fill, set, and empty each cooker
Evaluate ease of use and intuitiveness of controls for each model throughout testing
Compare stated versus actual maximum capacity of crocks when cooking
Weigh crocks and measure their depth
Test browning function, if included in cooker, by sautéing diced onions. Also brown and cook 3-pound boneless eye-round roast in recipe for Roast Beef with Warm Garden Potato Salad and compare finished roast to one browned in skillet and prepared in cooker without browning function
Check that 6-inch springform pan atop coil of aluminum foil fits inside crock (we use this setup in some dessert recipes)
A slow cooker promises to be a little fantasy grandmother who sits in the kitchen all day cooking for you, but use the wrong cooker and that dream could fizzle. A cooker might run hotter than expected, drying out the food or turning it mushy, or slower than you want, so dinner isn’t ready when you are. Then there can be issues with hot spots, which make food cook unevenly. And what if operating your machine is so confusing that you have to pore over the manual each time you use it?
For the ideal machine that would deliver a properly cooked meal and be absolutely simple and intuitive to use, we went shopping. Previous experience taught us that glass lids were a must, as they allow you to see progress without losing heat. So were oval-shaped crocks, as these can accommodate large roasts and offer more versatility than round crocks. We also wanted a generous 6- to 7-quart capacity. With these criteria in mind, we rounded up eight models priced from $39.99 to $148.71.
Slow cookers rely on covered moist-heat cooking, so of course we wanted to evaluate how well each model performed the classic task of turning a tough cut of meat tender. But since people use their slow cookers for much more than just braises and stews these days, we’d throw a few other recipe challenges at them, too. We chose recipes with a range of cooking times, using both low and high temperature settings. (Most recipes give you the option to cook for a shorter span on high or about twice as long on low. Generally the choice is about convenience, though delicate foods often require the low setting.)
Set and Forget?
We started by asking testers to evaluate how easy the slow cookers were to fill, set, turn off, and empty. Only the cheapest model in our lineup had a manual control (a simple dial, with no timer or automatic switch-off). We much preferred digital programmable cookers, which automatically switched to “warm” when the cooking time was up.
But setting the programmable cookers wasn’t always easy. We wanted intuitive controls, but several models had so many buttons with such confusing layouts that our testers couldn’t tell if they’d set them correctly. Then there was the “smart” slow cooker that ran via a phone app with such a pared-down control panel that it left most testers puzzled and frustrated. Yet another cooker’s controls let you set only even-numbered cooking times (2, 4, 6, 8, or 10 hours) and indicated cooking progress with a cryptic series of lights. But one model in particular was a pleasure to use: Its controls were unambiguous, each button clicked satisfyingly and lit up when pressed, and within a few seconds the clock began counting down so you knew that it was running.
Handling the slow cookers presented new challenges. Some handles became red-hot during cooking or were set too close to the hot rim of the housing. While we liked that the three products in our lineup that had metal inserts were featherlight and that we didn’t have to worry about cracking them, two of them became too hot to touch. Surprisingly, the heaviest crock in the lineup, a ceramic model, was also the easiest to use. It had protruding handles that were easy to grip and stayed cool. We found that this cooker was the only model that held close to the advertised capacity of 6 to 7 quarts and was also the only one with clear minimum and maximum fill lines.
It was time to start cooking. First up: braising chuck roast into pot roast. Two models produced mixed results, slightly overcooking some pieces and leaving others a bit underdone and chewy. A third model never rendered the meat fully fork-tender, even after extended cooking.
Next we made delicate boneless, skinless chicken breasts. Our recipe calls for laying four breasts in a row across the bottom of the crock. In three models (two of which were guilty of unevenly cooking the chuck roast), the breasts nearest the shorter, curved ends of the cookers cooked too fast. They climbed as high as 185 degrees, becoming dry and rubbery, before the pair in the center reached the target doneness temperature of 160 degrees. While cooking speed varied, all fell within the range indicated in our recipe.
Next up: turkey breast. In previous testings, we found that some slow cookers had a hot spot along the back wall of the cooker, which risked overcooking larger cuts that pressed up against it. This time around we were pleased to find that this hot spot wasn’t an issue, although one cooker that unevenly cooked chicken breasts overcooked the turkey where it touched the narrow ends of the crock. Again, cooking times varied, but all models finished within our time range of 5 to 6 hours on low.
Aside from the unevenly cooked chicken and turkey, all of the food was passable. But our front-runner produced evenly cooked food every time.
Under the Hood
Why did some cookers run fast and others slow? Why could some cook food evenly and others not? To find out, we dismantled a duplicate set of cookers with the help of Gregory Thiel, a postdoctoral associate in mechanical engineering at the Massachusetts Institute of Technology. Here’s what we found: Most of our models are “traditional” slow cookers, where food goes into a ceramic stoneware crock that absorbs and transmits heat slowly. These models had heating element strips made of nickel and chrome (“nichrome”) wire that wrapped around a fiberglass strip that belted the crock. When the cooker is on, this wire heats up more or less powerfully depending on the wattage and the setting. This construction tends to create hot spots near the element—particularly at the curved ends of the cookers, where the element surrounds the food more closely.
But two models with this belt-style construction actually did manage to cook food evenly, even at the ends. Opening up their housing revealed thick, heat-resistant padding and foil heat shields packed inside (the other models had been empty except for the heating element). The insulation buffered the pot from contact with the heating elements, preventing hot spots; it also explained why these two models—one of them our front-runner, from KitchenAid—tended to run a bit slower.
Two other models were designed very differently, with lightweight, nonstick-coated aluminum pots that sat directly on a hot plate with stove-style electric coils embedded inside that also heat more or less powerfully depending on the setting. This design encourages even cooking from end to end, though the thin metal pots of these slow cookers (by Cuisinart and Ninja) cooked hotter and faster than ceramic-crock models.
The remaining cooker was a hybrid style made by Crock-Pot, with a metal crock and a traditional belt-style heater. Like the other two models with metal pots, it cooked a little fast.
2. Heating Element:
Nichrome wire on fiberglass strip wraps around crock like belt. Strip is located around lower third of crock, enclosed in metal casing.
3. Two Layers of Insulation:
Buffer heat from element as it warms crock, preventing hot spots near element, and help conserve and employ heat efficiently.
4. Temperature Sensor:
Monitors cooking temperature and adjusts automatically to stay below boiling.
The KitchenAid model we liked so much has a useful feature: a sensor that automatically monitors and adjusts the cooking temperature so that it levels off and stays below boiling (ideally, food should stay at a simmer), helping further guard against overcooking food. Without such a sensor, the temperature of the crock pot’s contents will just keep climbing until it boils, whether set to low or high, simply because the heat is on (when set to low, it just takes longer to get there).
This was made clear in our next test: We tracked the temperature as each model heated 4 quarts of water over a period of 6 hours on high and then 12 hours on low.
The Fine-Tuned Path to Better Slow Cooking
Tracking the temperature as each slow cooker heated 4 quarts of water for 6 hours on high and 12 hours on low revealed that our winner, from KitchenAid, had a more-sophisticated design that kept heat at an even simmer. As the graph reveals, the water temperatures in all pots climbed quickly, but our top model made fine-tuned adjustments to keep the water temperature below boiling and hover around a target temperature. (Our runner-up did the same.) One of the worst-performing cookers, from Gourmia, had no temperature control sensor; the water temperature simply shot up until it hit boiling—it was no surprise that this model ran hot.
A Clear Winner
The KitchenAid 6-Quart Slow Cooker With Solid Glass Lid ($99.99), our former winner, handled every recipe with perfect results, albeit a bit slowly. Its thick stoneware crock, insulated housing, built-in thermal sensor, and crystal-clear controls put a well-thought-out design at your service—and at a moderate price. The Cuisinart 6-Quart 3-in-1 Cook Central ($148.71) is also a solid choice. It offers the advantages of a light, unbreakable metal crock with stay-cool plastic handles, as well as a brown-and-sear function that lets you skip using a separate skillet before slow-cooking in recipes that call for it.