Sous-vide is a method of cooking food sealed in airtight plastic bags in a water bath or
in a temperature-controlled steam environment 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 to 60 °C for meats and higher for vegetables. The intention
is to cook the item evenly, ensuring that the inside is properly cooked without overcooking
the outside, and retain moisture.
History The method was first described by Sir Benjamin
Thompson in 1799. 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 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, under-cooking 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 hydrolysed 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
while maintaining a firm or somewhat crisp texture. While the cell walls are generally
not burst, the de-polymerization of the pectic polysaccharides that connect the vegetable
cells together and/or the gelatinisation of starch in the vegetable can be achieved without
overcooking. Additionally, enclosed spices or ingredients
added to the food item transmit their flavor more intensely than during normal cooking.
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.
Temperature 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 piece of fish will cook in 17 to 18 minutes at any temperature from 44 °C
to 61 °C; 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 over cooked. 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. 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.
Pasteurize 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. Pasteurization is not always essential for safety if fresh uncontaminated food is
cooked and eaten immediately; fresh raw foods such as sushi and steak tartar are widely
eaten without ill effects. Food cooked below 55 °C will never be pasteurized, so the
recommendation is to stop the cooking when the target temperature is reached.
One limitation of sous-vide cooking is the fact that browning happens at much higher
temperatures. 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
and/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. 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
fish recipes, for example, are cooked below 55 °C. However, pasteurization 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 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 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 sealed within
the vacuum pack. The plastic used must not leach endocrine
disruptors. Many plasticizers used in plastics have these properties.
Uses
The sous-vide method is used in many high end gourmet restaurants by chefs such as Heston
Blumenthal, Paul Bocuse, Michael Carlson, Thomas Keller, Grant Achatz, Ferran Adrià,
Joël Robuchon, Philippe Rochat, Alessandro Stratta, Charlie Trotter, Michael Mina, Jason
Gibbins, John Tesar, 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 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. A more expensive, but more universally usable
solution is available in the form of combi steamers. Instead of a water bath, they feature
a tightly-controlled steam generation system. 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
cooking. Additionally, the high temperatures required for vegetables may melt the materials
of the average cooler. See also
Low-temperature cooking Slow cooker
References
External links Sous Vide Cooking Class from ChefSteps