Sous vide

Sous-vide cooking

Sous-vide (/suːˈviːd/; French for "under vacuum") is a method of cooking food sealed in airtight plastic bags in a water bath for longer than normal cooking times—72 hours in some cases—at an accurately regulated temperature much lower than normally used for cooking, typically around 55 °C (131 °F) to 60 °C (140 °F) for meats and higher for vegetables. The intention is to cook the item evenly, and not to overcook the outside while still keeping the inside at the same "doneness", keeping the food juicier.

History

The theory was first described by Sir Benjamin Thompson (Count Rumford) in 1799 (although he used air as the heat transfer medium). It was re-discovered by American and French engineers in the mid-1960s and developed into an industrial food preservation method. The method was adopted by Georges Pralus in 1974 for the Restaurant Troisgros (of Pierre and Michel Troisgros) in Roanne, France. He discovered that when foie gras was cooked in this manner it kept its original appearance, did not lose excess amounts of fat and had better texture. Another pioneer in sous-vide is Bruno Goussault, who further researched the effects of temperature on various foods and became well known for training top chefs in the method. As chief scientist of Alexandria, Virginia-based food manufacturer Cuisine Solutions, Goussault developed the parameters of cooking times and temperatures for various foods.

Essential features

As may also be done in traditional poaching, sealing the food in sturdy plastic bags keeps in juices and aroma that would otherwise be lost in the process.

By placing the food in a water bath whose temperature is set at the desired final cooking temperature of the food, overcooking can be avoided, because the food cannot get hotter than the bath it is in. In conventional high-heat cooking, such as oven roasting or grilling, the food is exposed to heat levels that are much higher than the desired internal cooking temperature; the food must be removed from the high heat prior to its reaching the desired cooking temperature. If the food is removed from the heat too late, overshoot occurs, and if it is removed too early, undercooking results. As a result of precise temperature control of the bath and the fact that the bath temperature is the same as the target cooking temperature, very precise control of cooking can be achieved. Additionally, temperature, and thus cooking, can be very even throughout the food in sous-vide cooking, even with irregularly shaped or very thick items, given enough time.

The use of temperatures much lower than for conventional cooking is an equally essential feature of sous-vide, resulting in much higher succulence: at these lower temperatures, cell walls in the food do not burst. In the case of meat cooking, tough collagen in connective tissue can be hydrolyzed into gelatin, without heating the meat's proteins high enough that they denature to a degree that the texture toughens and moisture is wrung out of the meat. In contrast, with the cooking of vegetables, where extreme tenderness or softness is seen as undesirably overcooked, the ability of the sous-vide technique to cook vegetables at a temperature below the boiling point of water allows vegetables to be thoroughly cooked (and Pasteurized, if necessary) while maintaining a firm or somewhat crisp texture. While the cell walls are generally not burst, the depolymerization of the pectic polysaccharides that connect the vegetable's cells together and/or the gelatinization of starch in the vegetable can be achieved without overcooking.

From a culinary viewpoint the exclusion of air is secondary, but this has practical importance: it allows cooked food to be stored, still sealed and refrigerated, for considerable times, which is especially useful for the catering industry; and it excludes oxygen from food that requires long cooking and is susceptible to oxidation, e.g., fat on meat, which may become rancid with prolonged exposure to air.

Limitations

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 either 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.

Special cases

The classic sous vide process involves two steps: Step One is sealing the food in air-tight bags, typically through the use of a vacuum pump/sealer. The term, "sous vide," or "under vacuum," though applied to the entire process, arose from just the vacuum-pump method of accomplishing just this first step. Step Two is the actual cooking of the food at low temperature for a prolonged time. A few sous vide foods are only subjected to Step One, a few are only subjected to Step Two, and many sous vide foods are never subjected to vacuum at all. Sous vide cookers can also step into the role of their more ancient cousin, the bain-marie.

Step One Only: Some high-end restaurants, such as those of Thomas Keller, bag fresh fruits, such as melons, place them in their vacuum chamber, and pull a high vacuum, causing the surrounding air to compress the fruit pieces into small, meaty jewels. These are then served in their vacuum-altered state having never been cooked.

Step Two Only: There's no reason to package a food in an air-tight bag if it comes pre-packaged, and one food comes naturally pre-packaged: The egg. Prolonged cooking of eggs in the shell at low temperatures is included in the category of sous-vide, although neither vacuum nor cooking bag is involved. The resulting egg is not a duplicate of an egg that has been boiled, with the outside typically hotter than the inside. Instead, the egg will be a uniform temperature throughout. As it happens, the yolk of an egg actually congeals at a lower temperature than the white, so it is possible to cook an egg with a solid yolk and a runny white. Thus a sous vide egg can be quite unlike anything that might be pulled from a boiling pot of water. (Cooking the egg at a higher temperature will see to it that both are firm.)

It can be desirable to have the food come in contact with the heating medium, as the medium itself can be an ingredient (for example, butter). At Thomas Keller's The French Laundry restaurant, their lobster tail are cooked into a sous vide cooker filled with Beurre monté (a butter specially prepared to withstand higher heat) as their heating medium.

Steps One & Two, But No Vacuum: Foods with liquids can be prepared for sous vide cooking in a normal water bath by placing them in zippered freezer bags, closing them most of the way, then gently evacuating the air until the liquid touches the zipper before completing the seal. Food thus sealed is just as well prepared for sous vide cooking as that placed under a vacuum. (The vacuum pump becomes more necessary when trying to evacuate all the air from a bag containing an oddly shaped object such as a pork chop.)

Crossing the Line: The dividing line between sous vide cookers and bain-marie water baths can become blurred. Crème Brûlée, for example, can be cooked in a sous vide cooker in bags using normal sous vide technique, then poured into waiting ramekin cups. Alternatively, with an appropriate baking rack, the ramekin cups can be set in the sous vide cooker, surrounded, but not covered by water, and the Crème Brûlée can be cooked right in the ramekins, taking advantage of the sous vide's extremely accurate temperature control, but cooked in the classic bain-marie fashion.

Modern use

The sous-vide method is used in many high end gourmet restaurants by chefs such as John Tesar, Heston Blumenthal, Paul Bocuse, Michael Carlson, Thomas Keller, Grant Achatz, Ferran Adrià, Joël Robuchon, Alessandro Stratta, Charlie Trotter, Michael Mina, Jason Gibbins, and others. Amtrak also uses this method for meals served on their trains, including Acela Express. Sous-vide has become a common feature on television cooking shows. It has also been used to quickly produce significant quantities of meals for hurricane evacuees. Non-professional cooks are also beginning to use sous-vide cooking.

Initially, enthusiasts used laboratory-grade thermal immersion circulators, often bought used on eBay and requiring very careful cleaning, even then not being recommended for kitchen use. Beginning in 2008, Auber Instruments and Fresh Meals Solutions made available comparatively inexpensive, yet highly accurate PID controllers with an attached thermocouple probe that could be used to control a commercial rice cooker, slow cooker, electric stock pot, or similar apparatus. In late 2009 the Sous Vide Supreme sous-vide machine (which does not circulate the cooking water) and Addélice swid immersion circulator, both intended for home use and less expensive than laboratory-standard equipment at a few hundred US dollars, went on sale.

It is possible to duplicate some effects of sous-vide techniques with the use of a beer cooler filled with warm water, checked with an accurate thermometer, and ziploc bags with the air sucked out to package the food for cooking. However, the heat loss involved in this technique makes it unfeasible for long-term (4+ hours) cooking. Additionally, the high temperatures required for vegetables may melt the materials of the average cooler.

Temperature control

The degree of accuracy and constancy of cooking temperature required varies with the food cooked. In some cases it is not critical; a 15 mm thick (0.59-inch) 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 coagulate at different temperatures, it is much more critical.

Cooking times

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 over cooked.

In sous-vide cooking you wait until the center of the food has reached its target temperature, but after this the food can never 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.

Once it reaches the target temperature, there are still three factors determining when to stop applying heat to the food, in order to:

• Inactivate the enzymes which may cause a mush-like texture in chicken after about 4 hours, and even less for fish.

• Tenderize tough meats, for example beef brisket and short ribs, which benefit greatly from very long cooking (48 to 72 hours).

• Pasteurise the food. If the food will not be eaten within 4 hours, it is beneficial to cook until the food is pasteurized. Both time and temperature are critical in this process (see below). Pasteurization is not always essential for safety if fresh uncontaminated food is cooked and eaten immediately; fresh raw foods such as sushi and steak tartare are widely eaten without ill effects. Food cooked below 55 °C (131 °F) will never be pasteurised, so it is recommended to stop the cooking when the target temperature is reached.

Safety

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 recipes such as fish are cooked below 55 °C (131 °F). However, pasteurisation of the food to be eaten by people with compromised immunity is highly desirable. Women eating food cooked sous vide while pregnant may expose risk to themselves and/or their fetus and thus may choose to avoid unpasteurised 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.

See also

• Food portal

External links

• Former Microsoft Genius Masters the Culinary Art of Sous-Vide - Wired
• Cooking Sous Vide
• Cooking Sous Vide the DIY Way - Popular Science
• An introduction to sous vide cooking and training courses
• How to build your own Sous Vide rig with off the shelf parts and an Arduino microcontroller.
• Setup Guide to Sous Vide Cooking at Home - Cooking For Engineers
• The sous vide page of the wikiGullet Project - The eGullet Society for Culinary Arts & Letters
• Over 50 Sous Vide recipes and videos, detailed information about functionality, recommended cookery books and much more.
• Video and step-by-step photos of sous-vide technique, applied to an egg
• SousVide Supreme water oven with recipes and information sources
• Nomiku Sous Vide Wand device developed via Kickstarter