Sous vide

Sous vide, or low-temperature, long-time (LTLT) cooking, involves sealing food in a plastic pouch or glass jar and immersing it in a water bath at a carefully controlled temperature. Cooking times are extended, typically ranging from one to seven hours, though some preparations exceed three days. The water bath is set much cooler than conventional cooking methods—around 55 to 60 °C for red meat, 66 to 71 °C for poultry, and higher for vegetables. This technique aims to cook food uniformly, so the interior reaches the desired doneness without the exterior overcooking, while also locking in moisture.

The concept of low-temperature cooking dates back to 1799, when Benjamin Thompson, Count Rumford, used air as a heat-transfer medium in a potato-drying machine and found that meat cooked this way was "perfectly done, and most singularly well-tasted." In the mid-1960s, American and French engineers developed vacuum sealing as an industrial preservation method, often called Cryovacking after the Sealed Air trade name. They noticed that vacuum-sealed food, even without heat, had improved flavor and texture, with fruits becoming more concentrated in taste.

French chef Georges Pralus adopted the method in 1974 at Restaurant Troisgros in Roanne, France. He found that foie gras cooked under vacuum kept its original appearance, lost little fat, and had a better texture. Another key figure, Bruno Goussault, became chief scientist at Cuisine Solutions in Sterling, Virginia, and in 1991 founded the Centre de Recherche et d'Études pour l'Alimentation (CREA) to study temperature effects on food. Through CREA, he trained top chefs and established precise cooking times and temperatures for various foods. Goussault and Pralus worked independently in the 1970s before collaborating, with Goussault marrying vacuum sealing to low-temperature cooking and Pralus, considered the father of modern sous vide, using higher temperatures.

Sealing food in sturdy plastic bags retains juices and aromas that would otherwise be lost. Placing the bag in a water bath set to the food's target temperature prevents overcooking, as the food cannot exceed the bath's temperature, much like a bain-marie. This precise control allows even cooking throughout, even for irregularly shaped or thick items, given enough time. In contrast, conventional high-heat methods like roasting or grilling expose food to temperatures far above the desired internal temperature, requiring careful timing to avoid overcooking or undercooking.

The low temperatures used in sous vide are essential. For meat, tough collagen in connective tissue can break down into gelatin without heating proteins enough to toughen the texture or squeeze out moisture. For vegetables, cooking below boiling prevents cell walls from bursting, keeping them succulent and firm while still allowing pectic polysaccharides to depolymerize and starch to gelatinize. Although excluding air is secondary from a culinary standpoint, it has practical benefits: it allows cooked food to be stored sealed and refrigerated for long periods (useful for catering), prevents oxidation of fats that can turn rancid, and improves heat transfer by eliminating trapped air in the bag. This method also promotes desirable flavors and limits off-flavors from oxidation.

The required temperature accuracy varies by food. For example, a 15-millimeter-thick piece of fish cooks in 17 to 18 minutes at any temperature between 44 °C and 61 °C, and could even be prepared in a switched-off slow cooker filled with hot water and a thermometer. For an egg, however, the precision is more critical.