What It Is
French for “under vacuum,” this surprisingly simple cooking technique is where food is sealed in a bag and placed in a water bath at a specific, constant temperature for hours—or even days—to slow-cook it to perfection. While ingredients are typically vacuum-sealed prior to immersion, similar results can be obtained by placing the ingredients in a regular Zip-lock bag or even a glass jar. (Pro tip: avoid cheap bags made with PVC.)
This is a similar water immersion technique to double boiling or bain-marie, except that with sous vide, the chef has a much wider range of temperatures to work with.
The Science Behind It
Sous vide is a much more forgiving cooking method compared to traditional styles of cooking like grilling, baking or broiling. Such methods often result in a wide range of fluctuating temperatures, which can make or break a dish in a matter of seconds—anyone who has tried grilling a steak to a perfect medium rare can atest to this.
In contrast, when using the sous vide method, an immersion heater or water bath is able to keep the water consistently below boiling temperature—typically between 129˚F and 160˚F for meats and 80 and 176˚F for vegetables. At these lower temperatures, food takes on a melt-in-your-mouth texture that many used to think could only be achieved by expert chefs with professional equipment. Juices and nutrients are also not leached from the ingredients, adding flavor and moisture to the final product.
Most chefs do a quick sear of the meats and vegetables just before serving the dish to give it that delicious brown crust.
The first sous vide machines were the stuff of science fiction, where NASA labs experimented with sealed-bag meals for astronauts in the 1960s. This technique caught on among French chefs in the '70s, with the original heavy duty commercial water baths largely being used exclusively in more avant-garde kitchens. It was only in 2010, when sous vide was popularized on the TV series MasterChef, that the first machines targeted at home cooks were launched. Today, sous vide equipment suitable for home use such as smaller water baths, immersion circulators and vacuum sealers are easily found in kitchen specialty stores, making this technique much more accessible to food lovers.