A sous vide immersion circulator is a sticklike appliance that heats water in a vessel to a desired temperature and then maintains that temperature to cook food immersed in the water bath. The food, which is first sealed in plastic (though not always; you can cook sous vide in glass jars, and eggs can be cooked right in their shells), eventually reaches the same temperature as the water, so it can’t overcook. With meat, poultry, and fish, you usually follow up with a quick sear in a skillet for surface browning.

The benefits of sous vide cooking are perfectly and uniformly cooked food and a process that’s quiet, neat, and mostly hands-off. Cleanup is minimal, because you’re cooking your food in water. And because they’re not cooked directly in the water, vegetables such as carrots and asparagus come out intensely flavorful and stay brightly colored. Sous vide cooking can also be long, slow, and gentle, turning tough cuts of meat fork-tender.

• Accuracy: The device must heat and hold water at a precise temperature; accuracy is everything in sous vide cooking.

• Speed: Our favorites rapidly reached the target temperature, shaving off many minutes of waiting around to begin cooking. Especially with short recipes such as poached eggs, faster-heating devices made a dramatic difference in the total cooking time.

Our top model, the Breville Joule, made tender poached eggs with runny yolks and cooked them right in their shells.

• Power: Devices that were more powerful circulated the water more efficiently, spreading the heat to maintain a uniform temperature in the bath.

• Simple, intuitive controls: Setting time and temperature should be easy and quick.

• Easy-to-read display: Being able to monitor progress without waiting for rotating displays or interpreting cryptic readouts was a major plus.

• Attachments that adapt to a variety of vessels: Whether we were cooking in an 8- or 12-quart plastic container, a 7.25-quart Dutch oven, or a large saucepan, our top models attached quickly and securely. We preferred devices with clothespin-like clips because we could secure them in place faster than those models with screw-on attachments. Our top model even has a magnetic base, so it can stand independently in metal pots.

Nice to Have

• User-friendly app: Two models are app operated, though one required the use of the app and the other also had controls on the machine. Our top choice has a simple, efficient app that let us set the device without fuss and monitor progress or make adjustments from afar. (The other, not so much; see below.)

• Compact size: Being able to store the device easily between uses without worrying about a bulky profile was a bonus.

• Higher wattage: Our top models had 1,000 watts of power or more at their disposal, helping them heat water and circulate it more efficiently.

• Inaccurate heating: Sous vide devices that don’t quite hit and hold the target temperature are frustrating. A single degree or two off target doesn’t matter much in an hours-long project such as pulled pork, but we found that even this small level of inaccuracy can affect food texture when preparing fast-cooking eggs or delicate vegetables such as asparagus. It’s a good idea to check the accuracy of your device with a separate thermometer; if the water temperature is consistently off, you’ll always need to adjust the setting up or down accordingly.

• Inefficient attachment modes: Circulators that attached to cooking vessels with screw-on clamps were more tedious to use than those with clips and they didn't fit as wide an array of vessels, including key pots such as a large saucepan or a Dutch oven. The screw-on device of one model was permanently positioned too high, making it impossible to attach the device to smaller pans. The placement of another model’s clamp made the device sit at an awkward angle when we attached it to a small pot or Dutch oven; sous vide circulators should be positioned upright in a vessel to work properly.

The screw-on device of one model was permanently positioned too high, making it impossible to attach the device to our Dutch oven.

• Confusing, tedious controls: Sure, you’ll get used to whatever device you choose, but the controls of some models were annoying and time-consuming to set. To select cooking times or target temperatures, we had to hold down arrows or repeatedly push buttons to scroll up or down; this was especially annoying when trying to select a 20-minute cooking time on models that started with defaults of 4 hours or longer. Another left us hanging for many seconds once we’d apparently set the time and temperature, and if we pushed the arrow again to get it started, it shut off. You get the drift.

• Displays that were hard to interpret: One model used the same display to show hours/minutes and temperature, so it always took us a second to figure out what we were looking at (Is that 18:00 hours or 180.0 degrees?).

• User-unfriendly apps: One model’s app kept losing connection with the device, which was very annoying when we wanted to change the timer, stop cooking, or check progress from another room (it happened repeatedly). Despite its user-friendly design, recipes, and tips, this frustrating app wasn’t worth it. When it was working, it allowed us to set exact desired times and temperatures. When it wasn't, we had to rely on the device's manual controls to set the timer, but we were limited to increments of 5 minutes—not too helpful when making a 12-minute egg.

• Do I need a vacuum sealer for sous vide cooking? 
A good vacuum sealer is really helpful to have when sous vide cooking because it extracts all the air from the plastic bag, enabling food to cook more evenly (any air pockets will block contact between the heated water and the food). Our favorite countertop vacuum sealer is the Nesco Deluxe Vacuum Sealer, priced at about $90. It’s fairly compact, very powerful, and simple to operate. If you don’t have a vacuum sealer, you can use a regular zipper-lock bag, such as our bulk-buy favorite, Elkay Plastics Ziplock Heavy Weight Freezer Bag, or our supermarket favorite, Ziploc Brand Freezer Bags with Easy Open Tabs. For the best results, you’ll want to remove as much air as possible to prevent air pockets. Here’s how to do it: Fill the bag and zip it partly closed, and then submerge most of the bag in the water, allowing the water to help squeeze out any air from the bag before you zip it fully closed. We sometimes double-bag foods with sharp edges, such as bone-in chops or veal shanks, to prevent the edges from poking through the bag or ripping a seam. You can use the same water-displacement trick to remove air from the second bag, too. Note: You can wash and reuse zipper-lock bags; just dry them fully between uses.

• Do I need to cover the water bath when I’m cooking sous vide? 
For recipes that cook in a few minutes, no. But we cover the vessel with plastic wrap during very long sous vide cooking sessions, such as our 20-hour pulled pork recipe, to help prevent too much water from evaporating. If the water level drops below the necessary minimum, the machine will shut down automatically (we checked!). Most will also sound an alarm or, if they have an app, send a notification to add water. Our winning plastic wrap, from Freeze-Tite, is so sturdy that we’ve found that we can reuse the same sheet many times. We like to cut a 3- to 4-inch slit in the middle of one side of the square of plastic so that we can wrap the cut edges snugly around the device and seal off the entire surface of the water bath. The minimum and maximum water-level lines required for sous vide cooking are marked on each sous vide machine. Always keep the water level between those two important lines.

• Is it safe to run a sous vide circulator overnight or if I’m away from home?
The short answer is yes, at least with the devices we tested. We ran all of them for 20 hours of continuous cooking in our home kitchens without incident when we made our Sous Vide Indoor Pulled Pork. For long cooking projects, we strongly recommend filling the vessel to the maximum water level marked on the device (check again after you’ve put in the food) and covering the vessel—but not the sous vide circulator—with plastic wrap to prevent water from evaporating. If the water drops below the minimum level, the machine will shut down. What’s more, if the power goes out, even briefly, you will need to manually restart the machine. Most of the devices we tested forgot their programming when they lost power and had to be reset. Our top model could be restarted via the app and did not lose its time and temperature settings.

• Prepare Sous Vide Soft-Poached Eggs, Sous Vide Seared Steaks, Sous Vide Perfect Asparagus, and Sous Vide Indoor Pulled Pork with each model, evaluating the devices’ performance, accuracy, ease of use, and their sturdiness of construction 
• Time how long it takes each device to heat 6 quarts of water in a Cambro plastic food storage container from 60 degrees to 160 degrees
• Compare the accuracy of the display thermometer on each device against two other calibrated thermometers, checking the water temperature in various locations throughout the vessel
• Compare water-circulation efficiency: Using single drops of yellow and blue food coloring, time how long it takes each device to turn 6 quarts of water uniformly green