In most cases, cooking sous vide simply involves two steps: the sealing of foods in plastic bags and submerging the bags into hot water baths for a period of time to heat through. The water is typically regulated at the desired final temperature of the food or just above. The food is held in the water bath until it reaches the same temperature as the water (and then held at that temperature until service or a final cooking step takes place such as searing). In many ways, this is similar to simmering (such as in a poached fish recipe), except the sous vide water is usually at a lower temperature and food is kept from making direct contact with the water by a barrier (such as a plastic bag or eggshell in the case of sous vide eggs, thus minimizing flavor and nutrient loss of the ingredients to the cooking liquid).Let's walk through what happens to the food while in the water bath with a concrete example. I'll use the example of a rib eye steak which I intend to cook to medium-rare. For the purposes of this example, I've vacuum sealed the steak after lightly seasoning with salt and pepper. The bagged steak is then deposited into a water bath set to 55°C (131°F). Its temperature starts off at refrigerated temperature of 5°C (40°F) and slowly rises over time as the heat from the water transfers through the bag and into the steak. Eventually, the entire steak will reach equilibrium at 55°C (131°F) - the exact time depends on the thickness of the steak. For most large rib eye steaks, one hour is sufficient for the entire steak to be at 55°C. At 55°C, the proteins we consider to be tough in raw beef have denatured (unraveled). (Raw beef is chewy because these proteins, called myosin, are intact. By cooking at temperatures higher than 50°C/122°F, myosin begins to break down making the beef more palatable.) There are other proteins in beef which, when denatured, are tough to chew. These proteins (actin), when denatured, also squeeze out a lot of water which causes the steak to become dry. At 55°C, the actin are more or less intact, thus preserving the tenderness of the beefsteak. At this point, the steak is "cooked" since it's reached the desired temperature and texture, but not necessarily safe to eat. Holding the steak at 55°C for an hour pasteurizes it making it safe to eat. (This pasteurization process kills most Listeria pathogens; however, at this temperature and time, salmonella can still be alive, but salmonella is not common in beef steaks. Salmonella can be an issue with ground beef which should be cooked longer to fully pasteurize. Had we set the water bath to 60°C (140°F), pasteurization time would have been only a few minutes - so sous vide cooking meats to higher levels of doneness takes less time than lower levels of doneness due to food safety concerns.)
At this point, the entire steak is at our desired final temperature - from edge to center to edge. Unlike other cooking techniques, there is no noticeable temperature gradient. When you grill a steak, the meat is placed over an extremely hot heat source and the outside layer of meat reaches temperatures in excess of 175°C (350°F). Under that layer is a layer of extremely well-done beef (much greater than 70°C/160°F which looks like grayish colored beef and is dry and chewy) which gradually becomes well-done, medium-well, then medium, and, finally (if the steak was flipped at the right time and pulled from the grill at the right time), a center which is medium-rare. If you like your steak medium-rare, then grilling a steak over high heat really doesn't produce much medium-rare beef. So, many techniques have been created to solve this problem - the two that work the best for me is to sear the outside of the steak (since the brown exterior is very flavorful and desirable) and move it onto a cooler (but still warm) part of the grill or placing the steak into an oven (even though the temperature of the oven is relatively high compared to the target temperature, air is a really inefficient conductor so heat transfers slowly into the meat providing more even cooking than a hot grill would have). This minimizes the amount of well-done beef in the medium-rare steak. Sous vide gives us an easy alternative to the oven, because, since we set the temperature of the water bath to the final internal temperature of the steak, it is impossible for the steak to overcook to medium-well or well-done. In fact, we can leave the steak at 55°C (131°F) for hours without being able to detect a difference in taste, texture, or flavor.
The only problem with sous vide steak is that the temperature never goes above our water bath temperature, so no surface browning can occur. That brown crust is one of the joys of eating a steak, so a quick sear on the hottest burner possible is all that is needed to finish the steak. This can be achieved with a very hot charcoal grill, a searing burner on a gas grill, infrared searing burner, a pan (people generally prefer cast iron) that has been superheated on the range, or a blowtorch (the medium sized ones from hardware store work much better than the small expensive kitchen torches). The hotter the heat source, the faster the steak can be browned, the more abrupt the temperature gradient you'll have in the steak. It should look something like: browned, medium-rare, browned with almost no discernable areas of well-done or even medium.
Sous vide cooking can be used to cook all types of proteins: fish, fowl, lamb, beef, etc. However, each type of meat has some differences in the proteins and denaturing temperatures. For example, in most fish, myosin begins to denature at around 40°C (104°F), while in mammals (beef, lamb, etc.) myosin doesn't denature until 50°C (122ˌF). The difference in protein denaturing temperatures in fish from other animals is one of the reasons why the tenderest fish is cooked at lower temperatures than beef or chicken. In fact, there are protein denaturing differences between types of fish - if we cooked salmon to 60°C (140°F), its proteins would have unraveled and tightened up so much that it would taste dry and perhaps even a little grainy. However, Mediterranean sea bass (also called branzino or dace) can be cooked to that same temperature without producing unsavory textures. In some meats with lots of connective tissue (such as beef ribs), long cooking times can be used to break down collagen into gelatin without bringing the meat up to the relatively high temperatures of 77°C (170°F) and above used when smoking ribs or braising short ribs. I'll cover the specifics of cooking various types of foods, the health concerns (which pathogens or parasites need to be considered or dealt with), and which proteins we're aiming at denaturing and which ones we want to avoid overheating in future articles.Eggs are of particular interest in sous vide cooking due to their complex composition of different proteins which denature at distinct temperatures. They can be cooked in their shells, so it's one of the easiest foods to experiment with once a temperature controlled water bath is set up. Just drop (well, place them gently so the shells don't break) them into the heated bath and wait one hour. Each one C° temperature change can alter the consistency of the egg white and egg yolk. My personal favorite is 65°C (149°F) where the yolk has thickened into a gel and the whites have taken on a custard-like consistency.
Vegetables can also be prepared sous vide, but the goal is the breakdown of starches. In general, this occurs around 85°C (185°F). For the most part, steaming, blanching, or sautéing vegetables produces almost the same result as sous vide. Because of this, I don't often bother to sous vide vegetables except for carrots, beets, and potatoes. When those vegetables are sliced or cubed, bagged, and cooked sous vide, you can get consistent texture through the entire piece without any liquid or nutrient loss to boiling water.
Disadvantages of Sous Vide Cooking
Expense. Cooking sous vide requires a temperature controlled water bath. This can be approximated on the least expensive end with either a large ice chest filled with hot water (measured with an accurate thermometer) or a large pot with a thermometer attached and a diligent cook adjusting the flame / heat source (potentially $0 cost if you already own a thermometer). On the expensive side, you can get what the professionals use - a piece of scientific laboratory equipment called an immersion circulator which regulates the water temperature and keeps it circulating to maintain a precise temperature within 0.1C° (these run at about $1000 and up). There is now a consumer water bath appliance on the market called the Sous Vide Supreme that runs about $450. In a future article, I'll discuss all the options from the $0 to the immersion circulator.In addition to the water bath, a vacuum sealer is needed (although using Ziploc brand bags should work when starting out - they are supposedly safe up to about 76°C/170°F). FoodSaver is the most popular brand and has offerings starting just under $100 to about $200. Chamber vacuum sealers are often used in restaurants and generally start at around $2000.
Time. It takes a lot of time to cook sous vide. Because heat transfers gradually from the surroundings into the ingredients, cooking always occurs at a faster rate when there is a large delta between the cooking environment and the food and slows down as the two temperatures get closer together. For example, placing a steak on a pan heated to over 500°F will transfer a large amount of heat (assuming the pan doesn't cool down too fast) into the steak rapidly. It only takes a few minutes to cook with such a heat differential. The same steak takes longer in the oven for two reasons: the temperature in the oven is usually lower and air is a poor conductor (when compared to metal cooking pans or water). Luckily, cooking sous vide is not as slow as the equivalent process in an oven (if both were set to the same temperature) because water is excellent at holding heat and imparting it (that's why we can stick our hand in a preheated oven at 175°C (350°F) for a while before feeling extremee discomfort while a few seconds at 85°C (185°F) in simmering water would give us severe burns). Unfortunately, the low temperature delta between food and heat source leads to long cooking times. In addition, since the food is often cooked at a lower temperature than flash pasteurization temperatures, once the food has reached its target temperature it should be held there for a period of time to ensure the destruction of pathogens, thus extending the total cooking time. (For foods cooked sous vide for short amounts of time with fresh ingredients, it is not necessary to pasteurize before eating by healthy adults.) For foods where connective tissue breakdown is desired, the cooking time could be days. (Of course, for some of these foods there are no alternative cooking methods that yield the same results.)
Temperature Limitations. You can't sous vide cook near the boiling temperature of water, so all cooking has to take place significantly below the temperatures needed to brown foods (Maillard reactions and caramelization all occur well above 150°C (300°F).) Also, no significant temperature gradients (which can be an advantage as previously mentioned) are present in the cooked food, so pan-seared salmon where the skin is crispy and textures range from well-done to rare are not possible. Another example where gradients are preferred is when soft boiling an egg such that the whites are solid and the yolk is running or gelled. Eggs cooked sous vide results in a uniform temperature and at 65°C the yolk has gelled and conalbumin (one of the major proteins in the whites) has denatured, but ovomucoid has not denatured which results in partially runny layers of whites. This can be solved with two water baths - one set to 75°C (high enough to denature ovomucoid but not ovaalbumin which causes whites to become rubbery) and another at 65°C. Setting the eggs in the first bath for just long enough to set the whites and then transferring them to the 65°C to be held for service.Another limitation related to temperature is that for any particular water bath, you can only have one uniform temperature. So, if you need to cook two things at the same time at different temperatures, you'll need multiple water baths. With some planning though, you can cook the hotter items first and lower the temperature and cook the lower temperature items while keeping the high temperature items warm at the lower temperature. For short periods of time (a few hours) this is usually not a problem.
Advantages of Sous Vide Cooking
Time. I previously mentioned that the amount of time it takes to cook sous vide was a disadvantage, but the type of time it uses can be seen as an advantage. For most of the cooking time, the cook is not active. You bag the food, heat the water bath, stick the bag in, and walk away for an hour (go to the gym, chat with guests, etc.) or a day or two (live your life normally - go to work, sleep, etc.). The food is safe and ready when you are to eat. With sous vide there is a large amount of flexibility. Eggs hold for a couple hours as do steaks. If the meat is done early, but you're not ready to eat - leave it in the water bath (unless it is fish or shellfish which contain enzymes which will work to soften the texture until it becomes mushy). If it's food that is cooked across multiple days, holding it another half day probably won't have any noticeable effect. If you changed your mind (or are working with fish or shellfish), shock the food down and refrigerate to be reheated in the same bag (properly shocked down and refrigerated most sous vide foods can be stored for a month in the refrigerator - indefinitely, in the freezer).
Temperature Control. Being able to target a specific temperature allows the cook to handpick which proteins should denature and which should not. This allows incredible control over texture. This control allows for the ability to cook foods in a way that are not possible through other means - gelatin rich medium doneness short ribs or medium doneness chicken breast. Another benefit of a temperature controlled water bath is the ability to pasteurize eggs in the shell at 57°C (135°F) and use them in place of raw eggs in recipes for the immune compromised (homemade mayonnaise, buttercream frosting, or even raw cookie dough).
Temperature Gradient. The slow cooking process and 0 difference between heat source temperature and desired food temperature means there is essentially no temperature gradient within the food maximizing the quantity of food at the desired temperature (and therefore the desired texture). No temperature gradient also means there is no carryover cooking and less of a need for food to rest.
Quantity Cooking. With an immersion circulator and a large water vessel, you can sous vide cook a LOT of food at once. Large bags of beaten eggs can be heated in a water bath to make scrambled eggs (a technique often employed at emergency shelter facilities). Chicken or turkey breasts can be vacuum sealed and cooked to produce large quantities of tender meat for use in salads or to be sliced with a rotary slicer (many industrial poultry breasts prepared for use by delis are cooked sous vide in the very bag they are sold to the deli or supermarket in).
Reduced product loss. Due to the vacuum sealing and a lower cooking temperature than most other cooking techniques, there is usually significant reduction in water and fat loss to the environment when cooking sous vide. Chicken, when cooked at 60°C (140°F) loses less than 20% of its weight (while frying, roasting, or grilling typically results in water loss of about 30%) resulting in more juicy chicken. The liquid isn't really lost either since it's captured in the bag and can be used for the basis of a sauce or gravy. In fact, it is rumored that the origins of sous vide cooking in restaurants began in France during the 1970's where George Pralus pursued this technique as a way to reduce product loss when preparing foie gras.
Temperature Control. Being able to target a specific temperature allows the cook to handpick which proteins should denature and which should not. This allows incredible control over texture. This control allows for the ability to cook foods in a way that are not possible through other means - gelatin rich medium doneness short ribs or medium doneness chicken breast. Another benefit of a temperature controlled water bath is the ability to pasteurize eggs in the shell at 57°C (135°F) and use them in place of raw eggs in recipes for the immune compromised (homemade mayonnaise, buttercream frosting, or even raw cookie dough).
Temperature Gradient. The slow cooking process and 0 difference between heat source temperature and desired food temperature means there is essentially no temperature gradient within the food maximizing the quantity of food at the desired temperature (and therefore the desired texture). No temperature gradient also means there is no carryover cooking and less of a need for food to rest.
Quantity Cooking. With an immersion circulator and a large water vessel, you can sous vide cook a LOT of food at once. Large bags of beaten eggs can be heated in a water bath to make scrambled eggs (a technique often employed at emergency shelter facilities). Chicken or turkey breasts can be vacuum sealed and cooked to produce large quantities of tender meat for use in salads or to be sliced with a rotary slicer (many industrial poultry breasts prepared for use by delis are cooked sous vide in the very bag they are sold to the deli or supermarket in).
Reduced product loss. Due to the vacuum sealing and a lower cooking temperature than most other cooking techniques, there is usually significant reduction in water and fat loss to the environment when cooking sous vide. Chicken, when cooked at 60°C (140°F) loses less than 20% of its weight (while frying, roasting, or grilling typically results in water loss of about 30%) resulting in more juicy chicken. The liquid isn't really lost either since it's captured in the bag and can be used for the basis of a sauce or gravy. In fact, it is rumored that the origins of sous vide cooking in restaurants began in France during the 1970's where George Pralus pursued this technique as a way to reduce product loss when preparing foie gras.
In future articles, I'll discuss the particulars of how to sous vide cook different ingredients as well as how to put together your own sous vide setup at home.