Sous vide
From The WikiGullet Project
 |
This article may need some polishing to bring it up to The WikiGullet Project standards. If you are a Society member, please consider taking a stab at fixing it. Have courage! |
Sous vide (pronounced /suːˈviːd/) is a cooking technique where food is sealed in vacuum bags and then cooked in a controlled-temperature water bath
(Temperatures should always be given in °C and °F. For convenience here is a Fahrenheit-Celsius-Conversion-Table).
Principles
Sous vide has become the name of a precise cooking method involving the use of heated water baths to cook food in a carefully controlled anaerobic (air-free) environment. The method typically involves the following steps:
- Preparing the food for cooking by seasoning, brining, or marinating it;
- Sealing the food in a waterproof plastic bag from which all air has been removed;
- Heating the food to a desired core temperature, either in water at that temperature or slightly above that temperature, and holding it at that temperature for short or long periods of time
- Removing the food and any released liquid from the bag; and, as desired,
- Finishing preparation of both by searing, making a sauce, and so on.
Following step three above, food can be chilled quickly in an ice bath in order to lower the core temperature sufficiently for safe storage. SV cooking is a technique with many other applications, including infusing foods with liquids or liquids with flavors, making custards or stock, and more.
Though it is just one of many cooking techniques available, SV is relatively new to restaurant cooking and very new to home cooking. As a result, many of the techniques are still being developed and refined. In addition, the precise nature of SV cooking requires careful calculation of not only familiar variables such as cooking time and temperature but also others involving thickness and core temperature that are less familiar to many cooks. Finally, due to the anaerobic conditions inside the bag and the low temperatures used, food safety issues are paramount.
Food safety and spoilage
In addition to usual kitchen hygiene, in sous vide cooking three more aspects have to be taken into account:
- Cooking at low temperatures does not kill pathogenic organisms or spoilage organisms.
- Pasteurizing at temperatures as low as 55°C/131°F will not kill all spoilage organisms.
- Vacuum sealing food creates an (at least partially) anaerobic environment allowing growth of and toxin production by e.g. clostridium perfringens and clostridium botulinum.
At temperatures used in cooking many plant products sous vide, i.e. at 80-90°C (176-194°F), pathogenic and spoilage organisms (except spores) are killed.
At temperatures used in cooking fish and tender meat rare to medium-rare (42-54°C / 108-129°F), pathogens are not killed and thus the time the product is outside of refrigeration should be minimized. In general when cooking at these low temperatures the product is served as soon as the desired core temperature is reached, and it is strongly recommended that the bath temperature be set 1°C/2°F above the desired core temperature to speed cooking.[1]
Poultry must always be cooked to pasteurizing conditions according to Douglas Baldwin’s table 4.1. If the sous vide system is not calibrated, either temperature or time should be augmented for safe pasteurization.
Long-time low-temperature cooking to tenderize tough meat should not be done below 54.4°C/130°F with a NIST or ISO calibrated system and not below 55°C/131°F with an uncalibrated system to comply with pasteurization conditions. Note that pasteurization conditions do not inactivate all spoilage organisms which may survive at higher temperatures. Pasteurized food may nevertheless be spoiled.
Equipment and techniques
Sous vide cooking is precision cooking at controlled temperatures. Thus the one most essential and indispensable piece of equipment is an accurate thermometer to control water bath temperature.
Vacuum machines and packaging
Food has to be separated from the water of the precision water bath. For liquid food this can be a solid container (pot). For solid food, it has to be a flexible containment, i.e. a plastic bag from which all air must be removed to avoid thermal insulation by air cushions (heat conduction in water is about ten times faster than in air). Air can be removed by immersing a bag in water to displace the air and closing with a sealing rod or with a ziploc. Alternatively and preferably, bags can be vacuum-sealed using either a clamp-type vacuum sealer or a chamber vacuum machine.
Clamp type vacuum sealers
These are the usual home vacuum sealers (FoodSaver and the like). They achieve a vacuum of about 80% (some more expensive ones up to 90%) which is more than sufficient for sous vide cooking. Sealing food which is not completely dry, e.g. marinated meat or fish with olive oil and lemon juice, may be difficult and tricky, but it is possible as described in an eGullet post by PedroG, provided the machine has an instant-seal-button and a side-port; this trick will not work with fully automated machines. Clamp type machines need special bags with a texture on the inside layer allowing air to be sucked across the sealing device.
Chamber vacuum sealers
These are professional vacuum machines. They achieve vacuum levels of about 99.9% which may be useful for some special purposes like vacuum compression and vacuum infusion, but which may dramatically and negatively alter the texture of proteins, especially fish and poultry, according to experiments by Dave Arnold of the French Culinary Institute. However Dave Arnold's findings could not be verified by eGullet members; see the discussion in the Sous Vide topic in the eGullet Forums (post #376 of 29 April 2011 - 11:20 AM to post #417 of 07 May 2011 - 02:06 AM. In view of these experiments, it may be prudent to use 99% vacuum (corresponding to a boiling point of 7.1°C) with food cooled to 4°C, thus avoiding eventual damage by boiling but removing sufficient air to avoid floating of the bags.
Vacuum sealing food with liquids is easy with these machines.
Water baths and PID tuning
Cooking sous vide necessitates a constant temperature water bath. Heat transmission from the surrounding medium is about ten times faster and more reproducible in water than in air.
Temperature accuracy and stability
A 1°C difference in temperature can make a difference in organoleptic outcome. A 0.5°C difference can make a significant difference in pasteurizing times. This implicates that temperature stability should be ±0.5°C or better for simple sous vide cooking (bringing food to temperature), and the sum of accuracy and stability should be ±0.25°C or better for long-time cooking and pasteurizing. This implicates using a reference thermometer of the required accuracy.
Unheated water baths
Short-time sous vide cooking may be achieved in a kitchen sink or beverage cooler filled with hot tap water of the appropriate temperature, eventually adding some hot water every few minutes.
Simple heated water baths
With some patience and baby-sitting, a large pot on a stove-top may be kept at the desired temperature. Better stability (±0.2°C) may be achieved with a large pot (7 liters up) in a convection oven, as described in a post in the eGullet Forums.
All-in-one controlled water baths
SVS, Julabo etc.
PID controlled self-heating cookers
SVM / Auber with rice-cookers, slow-cookers, electric stock-pots, Weck....
PID controlled immersion heaters
DIY bucket heater / PID-controller / circulation pump, SVM/FMM, SWID, SVP, laboratory IC.
Electrical safety
Should the electrical insulation of a sous vide water bath fail, there would be serious danger of electrocution.
A fuse or circuit breaker does not protect a person from electrical shock, it protects the house from an electrical fire in case of a short circuit.
To protect people from electrical shock, a ground fault circuit interrupter (GFCI) is necessary.
Most GFCIs do not resume after a power failure, so even a power failure of a second would switch the sous vide water bath off. A GFCI which resumes after power failure is preferable. In a moist environment a 10mA GFCI may be tripped, a 30mA GFCI is a better choice in this case.
Thermometers and their calibration
The importance of thermometer calibration
When cooking tough meat for enzymatic tenderization at 55°C/131°F for periods longer than 4 hours one is navigating between the Scylla of safety (min. 54.4°C/130°F to prevent bacterial growth and toxin production) and the Charybdis of overdoneness. A 0.5°C deviation of water bath temperature may change pasteurization times by 20%, see the article "Importance of temperature control on pasteurizing times". Thermometer inaccuracy plus waterbath temperature oscillation ideally should not add to more than ±0.25°C. When cooking below 54.4°C/130°F temperature accuracy is less important as this means cooking in the "danger zone" anyway.
Methods of thermometer calibration
The easiest and safest way to calibrate a sous vide water bath is using a high precision reference thermometer calibrated to NIST or ISO standards and calibrating the water bath at the crucial temperature of 55°C/131°F, placing the reference thermometer probe adjacent to the water bath controller's probe and allowing the bath to stabilize at 55°C/131°C. Temperature changes during calibration have to be avoided as different thermometer probes may have different thermal time constants. See also the necessarily incomplete market overview of reference thermometers.
A somewhat less reliable method is calibration at 100°F/37.8°C with a basal thermometer.
Another possibility would be calibration against a change of a substance that happens at a sharply defined temperature, like the freezing and boiling points of water, or the color change of a thermochrome; e.g. Bis(diethylammonium)tetrachlorocuprate reversibly changes from green to yellow at 52-53°C. Unfortunately, TLC (thermochromic liquid crystal) thermometers are of poor accuracy. Extrapolation from 0°C or 100°C to 55°C may be unreliable, as neither correct slope nor linearity are guaranteed, see the Wikia article on thermometer calibration.
More than one egg will be needed with Pierre de Serres' "poorman thermometer" (cited by Frank Hsu of FreshMealsSolutions):
Stabilize water bath at 59°C/138°C; discard the yolk of one egg, and place the white in a clear sandwich bag. Put the bag in the water bath. Within minutes the egg white will show:
- As clear as raw egg white which means 135°F/57.2°C or lower
- The thin white is milky and the thick white is clear which means 137°F/58.3C
- The thin white is coagulated and the thick white is milky which means 139°F/59.4C
- Both thin and thick whites are coagulated, which means above 140°F/60°C.
The latter method requires verification, as the temperatures are not in accordance with the temperatures in the egg cooking section.
Cooking Techniques, Temperatures and Times
There are two main techniques:
- Water bath temperature is equal to the final core temperature: minimal time to reach core temperature depends on thickness of the food item, but the food can be kept in the water bath for a longer time without substantial further change of texture and doneness; pasteurizing times depend on water bath temperature and food thickness. This is the typical sous vide cooking method, which is also used in Long time cooking to tenderize tough meat.
- Water bath temperature is above final core temperature (ΔT-cooking): cooking times depend on thickness and on the difference of water bath temperature and desired core temperature, and there will be a temperature gradient in the food which will equalize to some extent after removal from the water bath. This cooking method is usually reserved for special purposes like e.g. "the perfect egg".
Measuring thickness of food items
Thickness determines minimal cooking times and pasteurizing times. Measuring thickness may be facilitated by a thickness ruler which can be downloaded from the eGullet forums.
Cooking tender proteins
Tender proteins are proteins low in connective tissue, e.g. fish, most poultry, tender cuts of meat (beef, veal, pork, lamb etc.).
Fish
Fish of a quality allowing it to be eaten raw may be cooked to a rare to medium-rare doneness at the transition from translucent to opaque, i.e. to a core temperature around 45°C/110°F[2]. As parasites like Anisakis worms survive this temperature, it is recommended to freeze fish before use at -20°C/-4°F for 24h (European Union) to 7 days (U.S. FDA)[3]. When serving immune compromised persons, fish should be pasteurized according to Douglas Baldwin's Practical Guide, preferably at 60.5°C to avoid prolonged cooking times which might produce a mushy texture (see a post in eGullet forums by Douglas Baldwin. When vacuum-sealing fish, medium vacuums (i.e. 99% up) as produced by chamber vacuum machines should be avoided, because vacuum over 90% may result in a mushy texture of fish, as has been experimentally shown by Dave Arnold of the French Culinary Institute. Clamp type machines are ok, ziploc bags will do as well, especially when adding liquids like lemon juice and olive oil.
Poultry
Chicken and other poultry like turkey breasts should always be cooked to pasteurizing conditions according to Douglas Baldwin's Practical Guide. Most recommended temperatures are 63,5°C/146°F where pasteurizing times are almost equal to heating times, or 60.5°C/141°F with slightly longer pasteurizing times. Vacuum levels above 90% should be avoided, they might compromise the texture of poultry [1].
Meat
Tender cuts of meat like tenderloin, sirloin and rib-eye of beef or veal, lamb chops and lamb racks, filet mignon of pork, pork neck and pork chops may be cooked to the desired doneness (49-52°C/120-126°F for rare, 53-55°C/127-131°F for medium-rare, or 60°C/140°F for medium) after vacuum-sealing either as is or with a dry rub or marinade. Beef may become more tender by aging for a few days in marinade. Cooking times are given in Douglas Baldwin's Practical Guide.
Cooking tough proteins
Tough proteins are proteins rich in connective tissue, e.g. tough cuts of meat (beef, veal, pork, lamb etc.). The main component of connective tissue is collagen which can be converted to gelatin at higher temperatures, making the meat tender and succulent. Unfortunately, collagen starts shrinking above 60°C/140°F [4], squeezing out the juices and making the meat dry long before collagen is converted to gelatin at a considerable rate at temperatures above 70°C/158°F. Fortunately, collagen is also converted to gelatin enzymatically by collagenase at temperatures below 60°C/140°F,[5] although at a slower rate. In contrast to a few hours necessary for tenderization at temperatures above 70°C/158°F, it takes a few days (24-72 hours) at temperatures below 60°C/140°F; this implicates the danger zone has to be avoided, i.e. temperature should not be below 54.4°C/130°F. Recommended temperatures for LTLT (long-time low-temperature) cooking are 55°C/131°F to 57°C/135°F to achieve fork-tender succulent medium-rare meat. If a doneness comparable to traditional braising is desired, water bath temperature may be raised to 78°C/172°F for a few hours after enzymatic tenderization, thus avoiding dehydration by collagen shrinking above 60°C/140°F as collagen has already been enzymatically converted to gelatin below 60°C/140°F. Temperatures above 80°C/176°F should be avoided as actin gets denatured[6], making meat hard like shoe-leather [Citation needed].
Cooking eggs
Cooking eggs in the shell is not strictly sous vide cooking, but a temperature-controlled water-bath as used in sous vide cooking is a practical tool for cooking eggs.
Valuable information has been published at Khymos: "Towards the perfect soft boiled egg".
Douglas Baldwin posted the scientific background of egg cooking in the eGullet forum:
- The important temperatures and proteins when cooking an egg in its shell are:
- 143°F (61.5°C): the protein conalbumin denatures and causes the egg white to form a loose gel
- 148°F (64.5°C): the protein livetin denatures and causes the egg yolk to form a tender gel
- 158°F (70°C): the protein ovomucoid denatures and causes the egg white to form a firm gel (the egg yolk also coagulates around this temperature)
- 184°F (84.5°C): the protein ovalbumin denatures and causes the egg white to become rubbery
- The important temperatures and proteins when cooking an egg in its shell are:
Cooking eggs in boiling water for a time to achieve a creamy yolk will inevitably overcook the outer portions of the egg white, making it rubbery.
The solution is to cook eggs at a temperature between 70°C/158°F and 84.5°C/184°F ((ΔT-cooking)) so conalbumin and ovomucoid (but not ovalbumin) will be denatured, for a time to heat the yolk to a temperature around 64.5°C/148°F, yielding a soft-boiled egg with a firm but not rubbery egg white and a soft to creamy yolk. The cooking times at 75°C/167°F for eggs of different circumferences can be found in Douglas Baldwin's table "In-Shell Egg Heating Times in a 75°C Water Bath Using Circumference or Diameter"; note that these times are for eggs from the fridge. Measuring the circumference or diameter of the eggs is facilitated by an egg ruler or a caliper.
For fast and easy retrieval of the eggs from the water bath, suspending them in a net is recommended.
Cooking vegetables and fruits
Green vegetables may be blanched in sous vide bags in boiling water. This improves the flavor over traditional blanching by preventing water-soluble flavor compounds from leeching into the cooking water.
For vegetables where chlorophyll discoloration is not a concern, such as root vegetables, cooking at 85°C/185°F is commonly recommended.
Literal Translation of "sous vide"
The French phrase "Sous vide" translates literally as "under vacuum," referring to the vacuum that is used to remove air from the bags used to contain food in a water bath. However, the phrase "sous vide" (or SV for short) is often taken to mean "under pressure," [Citation needed] which is a misnomer: SV cooking neither involves cooking "under pressure" meaning above atmospheric pressure (e.g. in an autoclave) nor cooking at "under-pressure" meaning under a vacuum, i.e. at a pressure below atmospheric pressure. No matter how strong a vacuum was applied to remove the air, pressure in a plastic bag is always equal to atmospheric pressure provided the bag is not inflated by expanding gas.
Literature
Books
Online publications
eG Forums discussions and index
Chris Amirault has indexed the original eG Forums Sous Vide topic: that index may be found here. For the latest sous vide discussion, see the current eG Forums Sous Vide topic here.
This article is a stub. If you are logged in, you can help The WikiGullet Project by expanding it.
References
- ↑ Nathan Myhrvold, Chris Young, Maxime Bilet, Modernist Cuisine: The Art and Science of Cooking (The Cooking Lab, 2011, Amazon.com page)
- ↑ Harold McGee, On Food and Cooking: The Science and Lore of the Kitchen (Scribner, 2004, Amazon.com page), p. 207ff
- ↑ http://en.wikipedia.org/wiki/Sashimi#Safety_notes Wikipedia, Sashimi, Safety notes
- ↑ Harold McGee, On Food and Cooking: The Science and Lore of the Kitchen (Scribner, 2004, Amazon.com page), p. 152
- ↑ http://www.douglasbaldwin.com/sous-vide.html#Tough_Meat Douglas Baldwin A Practical Guide to Sous Vide Cooking, Chapter 2 “Basic Technique, Cooking, Tough Meat”
- ↑ Harold McGee, On Food and Cooking: The Science and Lore of the Kitchen (Scribner, 2004, Amazon.com page), p. 152
