Sous-vide is a method of cooking in which food is vacuum-sealed in a plastic pouch and then placed in a water bath or steam environment for longer than normal cooking times at an accurately regulated temperature much lower than normally used for cooking.
The degree of accuracy and constancy of cooking temperature required varies with the food cooked. In some cases it is not critical; a 15-millimeter-thick (0.6 in) piece of fish will cook in 17 to 18 minutes at any temperature from 44 °C (111 °F) to 61 °C (142 °F); such food can be cooked in a switched-off slow cooker filled with hot water and a thermometer. But for an egg, which has proteins that denature at different temperatures, it is much more critical.
Cooking times for normal cooking are determined by when the center of the cooked item reaches a few degrees below the targeted temperature. Then heating should be stopped immediately; while resting the food, residual heat will continue to cook it for a while. If the heating continues, the food will be overcooked. Sous-vide cooking continues until the center of the food has reached its target temperature; if it continues after this, the food will not be overcooked, and it will not cook more after it stops being heated. The time taken for the center of food to reach the target temperature depends on the initial temperature, the thickness and shape of the food, and the temperature of the bath.
One limitation of sous-vide cooking is the fact that browning (Maillard reactions) happens at much higher temperatures (above the boiling point of water). The flavors and ‘crust’ texture developed by browning are generally seen as very desirable in the cooking of certain types of meat, such as a steak. The flavors and texture produced by browning cannot be obtained with only the sous-vide technique. In many cases, meats and other foods cooked with the sous-vide technique will be browned before or after being placed in the water bath, using techniques such as grilling or searing on an extremely hot pan. This secondary browning is done briefly, and sometimes at higher heat than normally used, so as to affect only the surface of the food and to avoid overcooking the interior. Similarly, the skin of fish can be cooked at high temperatures after the sous-vide to make the skin crisp.
Food safety is a function of both time and temperature; a temperature usually considered insufficient to render food safe may be perfectly safe if maintained for long enough. Some sous-vide fish recipes, for example, are cooked below 55 °C (131 °F). However, people with compromised immunity should never eat food that has not been properly pasteurized. Women eating food cooked sous-vide while pregnant expose themselves and/or their unborn children to risk and thus may choose to avoid unpasteurized recipes.
Clostridium botulinum bacteria can grow in food in the absence of oxygen and produce the deadly botulinum toxin, so sous-vide cooking must be performed under carefully controlled conditions to avoid botulism poisoning. Generally speaking, food that is heated and served within four hours is considered safe, but meat that is cooked for longer to tenderize must reach a temperature of at least 55 °C (131 °F) within four hours and then be kept there for sufficient time, in order to pasteurize the meat.
Pasteurization kills the botulism bacteria, but the possibility of hardy botulism spores surviving and reactivating once cool remains a concern as with many preserved foods, however processed. For that reason, Baldwin’s treatise specifies precise chilling requirements for “cook-chill”, so that the botulism spores do not have the opportunity to grow or propagate. Pasteurised food can then be stored for up to two weeks at around 3 °C (37 °F) sealed within the vacuum pack.
The plastic used must not leach endocrine disruptors. Many plasticizers used in plastics have endocrine disrupting properties.