For part one of the primer, an introduction to low-temperature cooking and sous vide –including some funky charts– see here.

I got a bit long winded again.  I  intended to have Part II of this primer cover all forms of packing and preparing for low temperature cooking.  It was getting way too long – so here’s today’s installment.

II. Low Temperature Cooking Without a Vacuum.

… in which we’ll discuss preparing foods for low-temperature cooking without using a vacuum machine; we’ll look at zip-loc bags, plastic wrap, and cooking in oil/stock/humid air.

Before We Start: A Note from New York City:

New York City + No HACCP plan = no vacuum machines.

In New York City, a restaurant cannot use a vacuum machine without developing a HACCP plan.  HACCP (Hazard Analysis Critical Control Points) is a system designed to ensure food safety.  It was developed by large corporations who were making food for space missions –giving an astronaut food poisoning can be catastrophic. Creating your own HACCP plan (explained in the upcoming safety section of the primer), even if you don’t implement it fully, is a great way to help yourself ensure food safety. HACCP plans administered by the Board of Health, on the other hand, are a pain in the rear. They entail extra inspections, log books, lots of time, and possibly spending money on consultants. Look here for the Board of Health guidelines.  Low temperature techniques that do not require a vacuum machine have a major advantage for New Yorkers: no HACCP plan required. 

Even If You Don’t Cook in New York City:

While I love a commercial vacuum machine, about 90% of what a cook wants to accomplish with low temperature cooking can be achieved without a vacuum machine.  When Nils was at restaurant Aquavit he did a lot of low-temperature work with a circulator, but didn’t have a vacuum machine.  Back then restaurants weren’t required to have a HACCP plan;  he didn’t have a commerical vacuum because they cost too much.

Today many home cooks use the Food Saver vacuum for low temp.  I don’t use my Food Saver any more. I use Ziploc bags, without a vacuum.  I find Ziplocs easier than the Food Saver – I don’t have to hunt down the special bags, I can easily bag sauces (a pain with the Food Saver), I can bag hot foods (foods to be vacuumed need to be cold – more on that in the next primer installment).  My Food Saver has been relegated to potato-chip-bag-resealer.

To Review:  

Low temperature cooking is defined as any cooking procedure where the cooking temperature is at, or close, to the desired final internal temperature. There are two requirements for low-temperature cooking:

• precise and accurate temperature control
• a cooking medium which conducts heat more efficiently and accurately than dry air. Water and water vapor are typical; oil, stock, or any other liquid will work.

 
The Basics: To Pack or Not To Pack

There are two basic approaches to low temperature cooking:

• Expose the food to the cooking environment – includes cooking in temperature controlled poaching liquids, oil, 100% humid air. I call this “unprotected” low temp.
• Protect the food from the cooking environment – includes vacuum bagging (covered in the next installment of the primer), Ziploc bagging, plastic wrapping.

Unprotected Cooking Techniques:

100% Humid Air

You can’t cook low-temperature in dry air; for example, don’t try it in your oven. Dry air is a poor heat conductor and causes evaporative cooling at the surface of your food – making accurate temperature control impossible. 100% humid environments, like you can achieve in a combi oven, don’t conduct heat as well as straight water, but they can be very accurate. This kind of cooking is simple. Food goes into the cooker and gets pulled when it’s done; no wrapping required. The workflow is very intuitive for most cooks. But there are some disadvantages to 100% humid cooking; if you’re doing a cook-chill procedure the food isn’t protected from recontamination (it would be if it was wrapped); and during long cooking times (like several hours) the food’s surface tends to degrade.

Combi ovens and CVap ovens provide a 100% humid environment:

Combi Ovens

Combi oven.

Combi ovens are combination steam/convection ovens; modern ones can operate at low temperatures. The main advantage of combi ovens: they can  handle large amounts of food without getting bogged down by overloading, or by repeated opening and closing. Unfortunately, the ovens expend an enormous amount of energy to maintain this stability. Combis are also expensive and difficult to retrofit into many kitchens. And perhaps their biggest problem: they aren’t very accurate. Studies by Chris Young and Nathan Myhrvold show that while a combi oven’s average temperature can be accurate to within a couple of degrees centigrade, at any one moment it can be tens of degrees off. Combis should only be used to cook large items , like roasts, that won’t overcook in the ten minutes or so that it takes  the combi to swing back and forth around its target temperature.

CVap Ovens

CVap technology was originally developed for Kentucky Fried Chicken. Colonel Sanders needed something that would hold his chicken in perfect condition; he asked his friend and fryer guru, Winston L. Shelton, for help. In response, Shelton invented  CVap (Controlled Vapor) technology. CVap ovens are basically food holding cabinets with a bain marie in the bottom. Both the oven cavity and the bain marie are heated and temperature controlled. The cook can control the humidity inside the oven by adjusting the difference in temperature between the bain marie and the oven air. The core temperature of the food will not rise above the temperature of the bain marie. The surface texture of the food is controlled by the humidity of the oven air. You set the temperature of the oven air much higher than the water for crispy foods, like fried chicken, and you set it the same temperature for low temp cooking. For a detailed discussion of why the CVap works, see here.

CVaps come in many shapes and sizes, from very large down to single drawers like this one.

The inside of a CVap.

The Cvap comes in a range of sizes, is much cheaper than a combi, doesn’t require a lot of power, doesn’t require a water supply or a drain, and is extremely easy to retrofit. Many restaurants in New York City bought CVaps immediately after the Health Department  instituted HAACP control for sous-vide cooking. It is difficult to get a HAACP plan approved for sous-vide fish, and it is impossible to get one approved for fish below pasteurization temperatures (which is where we usually want to cook it). Since the possibilities of low temperature fish attracted many chefs to low temperature cooking in the first place, many took up the CVap.  It was basically unheard of in chef circles prior to the health department crack down. The disadvantage of the CVap:  it can start sucking wind if overloaded, or if the door is frequently opened and closed.

Cooking Directly in Water/Fat/Stock/Poaching Liquid

The immersion circulator is many cooks’ instrument of choice for low temperature cooking;  most cooks only use their immersion circulator with water. Take note: you can circulate any liquid you want –stock, beer, oil, duck fat, lard, apple cider, whatever. I am often asked if the circulator will be damaged by liquids other than water.  Happily, the answer is No.   If you ask Philip Preston from Polyscience (whose circulators we use) he will tell you the machines  aren’t NSF rated for direct food contact. It isn’t because the circulators aren’t safe for direct food contact, it’s just that getting the NSF rating would cost a lot more money than it is worth.  Here are the rules for unprotected cooking in the circulator:

• Make sure the circulator is clean.  Circulate detergent to clean it.  Scrub the heating coils with a toothbrush.  We use the oven cleaning tablets from our combi oven manufacturer to clean ours.  Those tablets eat everything.  Other people use CLR (calcium, lime, rust) remover.  Do what you like, but keep those circulators clean.
• Make sure you aren’t going to suck small items into your circulator pump. Any time you add herbs, burnt wood chips, crushed lobster shells, or any other flavoring to your bath, wrap it in cheesecloth first.
• Be careful, especially with oil and fat, to get good circulation.  Bad circulation = bad temperature control and could = safety problem. The cooking liquid should be moving around all sides of the food at all times.
• Never cook unprotected in a liquid that isn’t hot enough to kill bacteria.  We always keep our liquids above 54.4˚C (130˚F).

Tips for using a circulator to cook unprotected food. All of the parts that touch the cooking liquid are food-grade; but the machine isn't NSF rated for direct food contact because the rating would be too costly to obtain.

Unprotected Cooking in Liquid

Eggs are one of the few foods that we circulate directly in water. The whisk is just to keep them from rattling around in the circulated bath.

Eggs in their shells are cooked low temperature in plain water without any further protection –after all, they come pre-wrapped.  Most foods will have their flavors leached out if cooked in water (that’s how broth is made) but some foods benefit from cooking in stock or other flavorful liquid. These foods are prime candidates for unprotected low temperature cooking in liquid.  Fish can be cooked in a temperature -controlled court-bouillon.  Ham can be cooked in temperature-controlled apple cider. Bratwurst can be poached in temperature-controlled beer.  Most of the time, you are better off putting a small amount of your flavorful liquid in a bag with your food and doing protected low temperature cooking  – cooking directly in the liquid requires a lot of it.  Here are some cases where cooking directly in liquid makes sense:

• If you have an item too big to bag easily, like a whole ham, that could also benefit from some added moisture and some mellowing (many hams are salty)
• If you are cooking many of the same item over a period of time –like sausages:

 Let’s say you cook a couple hundred sausages a day. Start with a stock that complements your sausage. Use an immersion circulator to keep that stock at 60˚C (140˚F). Throw raw sausages into the stock to cook as you need them and pull out the cooked ones to finish on the grill. After a couple of hours your stock will take on a taste almost identical to your sausage.  The stock will taste like liquid sausage. I verified this phenomenon by paying five bucks to drink a cup of cooking water from a New York City hot dog vendor. After your stock has reached the liquid-sausage stage it is no longer changing the flavor of your sausages. The stock and the sausages are in equilibrium.  At the end of the day, throw some ice into your stock to cool it down and put it in the fridge.  The next day, bring your stock back to the boil to kill bacteria and start again.  If you added the right amount of ice the day before (determined by trial and error), you should be able to maintain a constant amount of stock indefinitely. In China, stocks have been continuously maintained this way for hundreds of years.

Getting liquid hot dog: cooking liquid in equilibrium with meat. Our intern Clifford scoped out the hot dog guy across the street, negotiated for a cup of precious hot-dog water, and got some.

Clifford with liquid hod dogs. This liquid smells and tastes exactly like a hot dog. It doesn't add or detract from the taste of the sausage. After hundreds of hot dogs were cooked in it, it is in equilibrium with the meat.

Unprotected Cooking in Fat

Circulating lamb directly in fat.

You can also cook directly in temperature controlled fat.  Fat doesn’t leach the flavors out of food and often provides a beneficial unctuousness. It is expensive to fill a whole circulating bath with fat, so use this technique in  circumstances like these:

• Some chefs and customers attach a stigma to cooking in plastic bags; fat poaching, however,  has an aura of tradition and wholesomeness
• If you are cooking a lot of the same item, it can be convenient to cook directly in fat.  No time is required for bagging. It’s  much faster to pull items directly out of a fat bath than to un-bag them.  The cost of the fat is less significant over a large number of items
• Very large items –like a 36 inch striped bass –can be difficult to bag, and you might not want their flavor altered by a stock.  Cook them directly in oil or fat.

36 inch striper circulating in fat. All of the containers and other stuff in the bath is to minimize the amount of oil needed.

Protected Low Temperature Cooking

Most low temperature cooking work involves protecting the food from the cooking medium with some sort of impervious cover, which is almost invariably made of plastic.  The advantages of protected cooking are:

• There is no loss of flavor to the cooking medium.
• There is a reduced risk of contamination. 
• Different types of foods can be cooked in the same vessel at the same time.
• Protected foods are very easy to chill quickly after they are cooked.

The main disadvantages to protected cooking are the time it takes to wrap or bag the food, and some people’s trepidation about cooking in plastic.

Cooking in Plastic:

Many people are concerned about the possibility of chemicals from plastics leaching into foods during cooking.  I haven’t been able to get any firm data on the migration of plastic materials from bags and plastic wraps into food, but I’m fairly certain that at least a small amount of migration is likely to occur. Whether or not that degree of migration is harmful is up for debate.  

Many people are currently worried about the plasticizer Bisphenol A (BPA).  Here is what the US government has to say about it.  BPA is used primarily in polycarbonate.  While we don’t wrap foods in polycarbonate, low temperature cooking is often done in polycarbonate containers (eg Lexans or Cambros).

Polyvinyl Chloride, another commonly used kitchen plastic , contains a whole mess of plasticizers –usually a group of chemicals called phthalates.  As far as the PVC industry is concerned, phthalates cause tumors in rodents but not in primates –even in larger than normal doses. Other people are not so sure. Who knows? Many commercial plastic wraps are made of PVC.  Often, these wraps smell bad –indicative of residual solvents and whatever is was used to make them.  Aside from any purported health issues, bad smelling plastic wrap can most definitely make your food taste bad. Fatty foods like cheese are more likely to pick up bad odors from plastic wrap. Don’t use plastic wrap that smells bad.  On the positive side, PVC is a pretty good vapor and moisture barrier and can have pretty good heat resistance.

 Polyethylene, in its many guises, is another major plastic used to wrap foods. Most supermarket plastic wrap is made from polyethylene (PE).  Polyethylene is usually plasticizer free –which is good news.  Polyethylene wraps usually have some chemicals added to increase cling –often ethyl vinyl acetate (EVA) and polybutene (PIB).  I haven’t found any health concerns on these two ingredients.  The bad news about polyethylene is that it doesn’t tolerate very high temperatures and it is not a very good gas barrier. Plastic wrap is an especially bad gas barrier because it is made from low density polyethylene (LDPE).  Food wrapped in LDPE will still oxidize.  Odors might also be able to penetrate LDPE. Use several layers.  Ziploc bags, as far as I can determine, are usually made of polyethylene.  The freezer Ziplocs are better gas barriers than standard Ziplocs, both of which seem better than plastic wrap.  Perhaps Ziplocs are just thicker than plastic wrap, maybe they contain some other type of polyethylene.  I don’t know.

Packing Without the Vacuum:

Ziploc Bagging:

Ziploc bags are excellent cook-chill tools.  At the school we always call out Ziploc, rather than re-sealable bags, because many off-brands don’t work.  The seals fail, the bags come apart when cooking, etc.  Do not purchase the Ziploc with the sliding do-dad.  Get the regular double-seal type.  We buy the freezer storage bags because they are supposed to act as a better vapor barrier than the regular type, and they are rated for re-heating in the microwave.  We stock quart and gallon size bags.  If you learn the proper technique for bagging, Ziploc bags can get almost as tight as a vacuumed bag.

The Technique:

1. Fill a container with water deep enough to easily submerge your food and bag.
2. Always add some sort of liquid to the bag –fat, stock, sauce, etc.  The liquid is necessary to fill the gaps around your food and expel the air from the bag. 
3. Add your food item.  A significant advantage of Ziplocs over vacuum bags is that the food can be added to the bag hot.  All vacuum bagging procedures require your food to be cold (more on that in the upcoming vacuum section of the primer).  If you are searing meat and adding it directly to the Ziploc bag make sure the surface of the meat is below 100˚C (212˚F) or the bag will melt.  Be especially careful to not touch the bag with a hot set of tongs or spatula.
4. Close the seal of the bag almost to the edge, leaving the last portion of the seal open –make sure you have correctly sealed the bag.  Put your finger in the corner to make sure that part of the seal is open.
5. Carefully immerse the bag in the water starting with the  closed corner, not the open one. Make sure you do this step carefully,  allowing  air to escape up and out of the open corner.
6. Just as the open part of the seal is about to go under the water, close it up.

1. Fill a container with enough water to submerge your product. 2. Make sure there is liquid or oil in the bag. Add your product and seal the bag except for one corner. Put your finger in the open corner and start submerging your bag like it shows in the picture. Submerging as shown will minimize the amount of trapped air.

1 and 2. Submerge the bag and work out all the air. 3. Just before the last corner goes underwater, remove your finger and seal the bag completely.

Finished Ziploc. No air bubbles. Almost as good as a vacuum.

The advantages of the Ziploc are:

• you don’t need to buy a vacuum
• food can be bagged hot
• food can be removed from the bag and re-bagged easily
• the process is very gentle on foods and doesn’t change food textures the way vacuum bagging can
• it’s just as effective for cooking as vacuum bagging for most items

The disadvantages of the Ziploc are:

• not as convenient for bagging a lot of items as the vacuum machine
• Ziplocs cost more than vacuum bags
• doesn’t provide some vacuum benefits –fast marination, extended storage, oxygen removal.

Wrapping in Plastic Wrap:

Rolling foods in plastic wrap is an excellent preparation technique for low temperature cooking. Rolls cook evenly and are easy to portion.  We often combine rolling with some meat glue (see the transglutaminase primer).  Properly rolled roulades in plastic wrap will not allow water to penetrate.  Really good rolls are dense –they will sink.  Here is the technique in pictures, borrowed from our transglutaminase primer.  Remember –making good rolls isn’t as easy as it looks.

Another option for plastic wrapping: the cannon ball.  Place the food to be cooked in a square of plastic wrap and twist to form a ball.  Tie up the loose end.  The part of the cannonball near this loose end isn’t going to be very pretty –serve it face down on the plate.

1. Mis en place for the cannonball. Plastic wrap and either butchers twine or a length of twisted plastic wrap to tie off the ball. 2. Put your product in the center of the plastic. Normally, we would add some meat glue.

1. Gather up the meat. 2. Use your hand to squeeze out most of the air and form the ball. 3. Make sure to get out the air at the point where the plastic wrap comes together.

1. Twist the cannonball to form the shape. 2. What your cannonball should look like.

If there are large air bubbles in the ball you can poke them with a skewer and they will go away. If you poke the wrap with a skewer you'll need a second layer of plastic.

1. Place the cannonball in another piece of plastic wrap. 2. Squeeze the air out and reinforce the ball shape. 3. Twist to lock.

1. Tie the cannonball off. If you use string as pictured, be careful to not rip the plastic. Tying with plastic minimizes this risk. 2. The finished cannonball.

The underside of the cannonball looks a little wonky. Serve this side down.

Whenever you use plastic wrap, use a brand that doesn’t smell bad.  If you are worried about phthalates, use polyethylene  instead of PVC.

Next installment: the vacuum machine. 

We have had a lot of requests to make last week’s low-temp charts available for download. Here you go: 

Click here to download the sous vide charts.

We are often accused of being long-winded. Guilty. When we looked at the sous-vide primer, however, even we thought it was too long—so we decided to break it into parts. We hope to put out a new section every week (or so). This is how we plan on breaking it down:

• I . Introduction to Low-Temperature Cooking and Sous-Vide (Today’s Installment)
• II. Use and Abuse of the Vacuum Machine and Packing for Low-Temp Without the Vac
• III. Vacuum Tricks
• IV. Temperature Control and Safety
• V. Cooking Meats and Poultry
• VI. Cooking Fish
• VII. Cooking Everything Else

Today we have the introduction. It provides an overview for everything else. There won’t be any specific applications or how-to’s in this section. That is for later.

Part I. Introduction to Low-Temperature Cooking and Sous-Vide

• I. Getting the Terms Right
  • Low-Temperature Cooking Defined
  • Sous-Vide Defined
• II. Some Uses and Advantages of Low Temperature Cooking
  • Uniform Cooking, Increased Consistency, and Shifting Control to the Chef
  • Shifting Work from Service to Prep (or from Party to Prep at Home)
  • Low-Temp for Insurance
  • Low-Temp for New and Novel Textures
  • Low-Temp for Increased Tenderness
• III. Low Temperature Cooking Disadvantages
  • Surface Browning, the Maillard Reaction, and the Challenges of Low-Temperature Cooking
  • Uniformity of Texture
• IV. Why do Chefs Use Sous Vide?
  • Sous-Vide for Economy
    • Storage
    • Organization
  • Sous-Vide for Effect
    • Texture Modification
    • Flash Pickling and Vacuum Marination
    • Forming
    • De-airing

I. Getting the Terms Right:
Sous-vide and low-temperature cooking are just two of the many techniques and processes that are revolutionizing modern cooking. Despite their growing popularity, many remain confused about the difference between low-temperature cooking and sous-vide—including equipment manufacturers. Between the two, low-temperature cooking is undoubtedly the more important.

Low-Temperature Cooking Defined:
Cooking low temperature does not mean cooking food to a lower internal temperature than is traditional. Low-temperature cooking refers to the temperature of the cooking medium, not the final temperature of the food being cooked. A rare steak has the same internal temperature whether cooked low-temperature or traditionally. Low temperature cooking is defined as any cooking procedure where the cooking temperature is at or close to the desired final internal temperature. There are two basic requirements for low-temperature cooking:

• precise and accurate temperature control;
• a cooking medium which conducts heat more efficiently and accurately than dry air. Water and water vapor are typical, but oil, stock, or any other liquid will work.

By way of example: to cook a steak to an internal temperature of 55°C (131°F), you could either sear it and put it in a 205°C (400°F) finishing oven till it reaches 55°C (131°F) (not low temperature cooking), or quickly sear it and throw it into an oil bath maintained at 55°C (131°F) (low temperature cooking but not sous-vide).

In traditional high-temperature cooking, the temperature of the cooking medium is almost never the same as the desired temperature of the food. That is, while your oven may be heated to 205°C (400°F), your fry oil can to 190°C (375°F), and poaching water to 100°C (212°F), a steak cooked in those mediums can only be considered rare when it reaches an internal temperature of 54°C (129°F). The difference between the desired final food temperature and the temperature of the cooking medium is referred to as temperature delta, or ΔT (pronounced “delta t,” the triangle is the Greek letter delta). You should just get used to referring to ΔT’s –like, “hey, you want that squab cooked to 56°C? Do you want to use a ΔT?”

Sous-Vide Defined:

In contrast, the simplest way to define sous-vide may be to refer to its French meaning, “under vacuum.” Anything associated with a vacuum machine is sous-vide. In restaurants, the sous-vide process usually (but not always) consists of:

• placing products into impervious plastic bags
• putting those bags under vacuum
• heat sealing those bags
• releasing the vacuum
• further manipulating, processing, or storing

This is where it gets confusing: sous-vide techniques are often used for low temperature cooking, but not all sous-vide cooking is low-temperature cooking. The classic example of this is boil-in-bag meals. The cooking medium is boiling water—not low temperature. Yet, because there is a vacuum process involved, it is sous-vide. That said, sous-vide is very effective for low-temp cooking because food inside the bags neither dries out nor loses flavor during prolonged cooking if proper temperature is maintained. The vacuum bags also eliminate evaporation and evaporative cooling. The temperature of the food’s surface becomes identical to the cooking temperature after a short time.

Chefs and diners alike often confuse sous-vide and low-temperature cooking. Sous-vide must involve a vacuum process; but the food may be cooked at high or low temperatures. About 90% of what cooks want to achieve with low temperature cooking can be achieved without a vacuum.

II. Some Uses and Advantages of Low Temperature Cooking:

Uniform Cooking, Increased Consistency, and Shifting Control to the Chef:

Traditional steak vs. low-temp steak.

Traditional cooking typically uses a high ΔT. Foods cooked in this manner display an overcooked portion on the exterior. Meat cooked at high temperatures does not have one level of doneness—it is tasted as an average, from the well-done exterior to the less cooked center. Low-temperature cooking is less forgiving, because there is no way to average out errors. In a steak cooked at a low ΔT, the steak retains the same temperature throughout. The difference of 2°C can make a large difference in texture when there is no averaging effect—you need good temperature control (The entire range of steak doneness, from rare to well-done, is only a matter of 14°C (25°F). Luckily, modern equipment easily gives us temperature control accurate down to a tenth of a degree, which means we can cook products extremely uniformly and get them right 100% of the time.

Uniformity can be a disadvantage—no one wants a giant piece of roast beef that is one color all the way across—but most of the time uniformity is an advantage because it leads to increases consistency. Your steaks will never be over or under –always just right. This advantage cannot be overstated, and it applies to restaurants or home cooks. Additionally, because the hard work of reaching the correct internal temperature is being regulated by an accurate piece of equipment, the responsibility for getting the product right is shifted away from the line cook towards the chef who is choosing the temperature and setting the machine.

Shifting Work from Service to Prep (or from Party to Prep at Home):

We can always make more prep time. Service is what service is. Any time we can shift work away from service towards prep we win. Many low temp techniques require more prep time than their traditional counterparts; but are blindingly fast to finish off at service time. The high speed finish derives from the fact that the food is pre-cooked and can be held warm and ready to go, only needing a few seconds of finishing time. Speed finishing is a boon to the home cook as well. Parties are a lot more fun when you can hang out with your guests and all your food is in perfect finish at the same time.

Low-Temp for Insurance:
Low-temp cooking can provide a type of cooking insurance by guaranteeing a minimum doneness. Here’s how:

1. Low temp your food to the rarest you want it. The food is now uniformly rare.
2. Cool the product completely.
3. Cook the product traditionally, but focus only on obtaining the perfect exterior because the middle is already cooked. You have insured that the inside is done.

Here are some examples of low-temp for insurance:

• Roasts can be challenging. Often you get a good crust before the middle is done and then overcook the whole piece to bring up the center. Other times, you focus on getting the middle perfect but end up with a poor crust. Low-temp insurance fixes that. Low temp the roast till it is rare and cool it down. Put the roast in a high oven and pull it when the crust is perfect—you have already insured that the middle is done.
• On a beef Wellington it is very difficult to insure that the puff pastry and the beef come out nicely at the same time. Usually the meat is overcooked or the pastry is too blond. With low-temp insurance you sear and pre-cook and cool your tenderloin and then wrap it in puff pastry. Now, you can turn your oven up and just focus on getting the pastry nice and brown since your meat is already cooked.
• Sausages are often poached before being finished in a pan on the grill. This is high-temp cooking insurance. Instead, low temp-cook the sausages (60-62°C is usually good), then finish them on a grill or in the pan. The low-temp pre-cook doesn’t overcook the meat and rely on fat alone to provide juiciness.
• Duck breast is best cooked with low-temp insurance. Pre-cook the breast to 57°C and cool it down. Then just focus on crispy skin.

Low-temp for insurance tends to produce items that have textures and appearances very close to traditionally cooked items, just better and more consistent. Because the products have a traditional feel, many cooks like this technique.

Low-Temp for New and Novel Textures:
Low-temperature cooking also allows for the production of some textures that were traditionally unattainable. Three examples:

• Super-low temp fish: Fish heated at extremely low temperatures, around 50°C or (122°F) to an internal temperature of 42°C (107°F), has a dense, fudge-like or custard quality unattainable with high ΔT cooking. This type of cooking is controversial; many chefs dislike the texture attained with these methods, and some scientists believe the techniques are unsafe. Other chefs believe that the traditional cooking method overcooks fish and that the low-temperature method is best.
• Low temperature braises: In a typical braise, meat with a lot of connective tissue is cooked at a high temperature for several hours. The high temperature and several hours is what is needed to break down the collagen into gelatin. This process overcooks the muscle and dries it out. Luckily, the gelatin re-moistens the overcooked meat and produces a delicious braise. When a meat is under-braised, it seems tough and dry because the collagen hasn’t melted into juicy, water holding gelatin. With low temperature cooking, however, we can hold a tough piece of meat at a very precise temperature for a very long time. If a short rib is held at 6o°C (140°F) it will maintain a lightly pink, medium-cooked color for days. The texture of the muscle fiber itself will also remain somewhat static. The connective tissue, on the other hand, won’t break down over the course of 3 or 4 hours at this temperature—you need to cook it for two full days. At the end of these two days, however, you will have a completely pink, completely tender short rib that is a dream to slice and portion.
• Creamy egg yolks: When you heat a whole in-shell egg in water to 63°C (145°F), the yolk becomes creamy—not runny, not set. One degree lower is a runny yolk. One degree higher is a set yolk. The 63°C egg is a delight and completely impossible to make traditionally. More on eggs later.

Low-Temp for Increased Tenderness:

Low-temperature cooking can also produce meats that are more tender than normal. Enzymes responsible for some of the benefits of dry-aging meat increase activity as the temperature rises. These enzymes are most active right before they denature, between 49°C and 54.4°C (120°F and 129.9°F). Because low-temperature cooking allows meat to stay in this zone longer than traditional cooking, meat is more tender than normal. Traditionally, a large piece of meat heated for a long period of time, such as a roast, remains tender. Low-temperature cooking makes it possible for smaller pieces of meat to be held at these low temperatures for longer periods of time.

III. Low Temperature Cooking Disadvantages

Surface Browning, the Maillard Reaction, and the Challenges of Low-Temperature Cooking:

Low-temperature cooking does not produce crisp, flavorful, brown exteriors, which are usually obtained by cooking at high temperatures. Much of the artistry of low-temp cooking involves getting around this limitation. Some techniques include:

• Using meaty, savory flavors like soy sauce and miso (both are high in umami).
• Quick-searing meats for flavor either before they are cooked, right before they are served, or both. Quick-searing in low-temperature cooking is performed at a higher than normal temperature to develop a brown crust without overcooking the interior of the meat.
• Browning bones, fat, inexpensive pieces of meat, or vegetables and putting them into the vacuum bag along with the main food before cooking. The savory notes of the added pieces permeate the food over time. Roasted fat is especially useful, as many of the characteristic flavors of different meats are generated by the taste of cooked and broken down fats.

Uniformity of Texture:

The biggest gripe people have with low-temp cooking is that the uniformity of texture. Some people say that all low temp food is “mushy.” While it is true that bad-low temp food is mushy, good low-temp food doesn’t have to be. One of the ways to guard against uniformity is to provide texture in the finishing step—usually by searing. Adding crunchy garnishes or cooking portions of the food separately to compensate for the lack of textural variety is another option. A chicken breast cooked sous-vide, for example, might be served with a piece of crispy fried chicken skin (although we have had good chicken this way, we find the skin served this way not as satisfying as good-old crispy skin that is still stuck to the chicken). Lastly, European chefs often cook with a moderate ΔT (usually 10-15 C) to “overcook” the outside of the food and provide some textural variation. Most Americans don’t cook this way because it require precise temperature measurement, precise timing, or both. Most Americans cook with 0 ΔT and add texture in the finishing step.

IV. Why do Chefs Use Sous-Vide? Sous-Vide for Economy and Sous-Vide for Effect
Chefs may use sous-vide techniques and processes for a variety of reasons which roughly break down into two categories: sous-vide for economy and sous-vide for effect. The two approaches are not mutually exclusive, therefore it’s important to thoroughly understand both.

Sous-Vide For Economy:

Storage:

Traditionally, vacuum-packing has been used to enhance the storage life of cooked products. The bacteria that cause food spoilage need oxygen to survive. Since vacuum packaging removes all air (and therefore oxygen) from food, spoilage is slowed drastically if the proper steps are taken. Oxidation is also greatly reduced by utilizing vacuum-packing. Foods like cut apples and artichokes do not turn brown quickly in vacuum pouches. In long-term storage, vacuum bags can prevent the oxygen-produced rancidity of unsaturated fats. Low-moisture products like dehydrated fruit chips tend to stay crispy indefinitely in the low-moisture vacuum environment.

Unfortunately, some bacteria that cause illness (pathogens) are not inhibited by a lack of oxygen. In fact, some of the most dangerous bacteria thrive only in the absence of oxygen. If sous-vide products are kept in unsafe conditions, these pathogens can grow to dangerous levels without the simultaneous spoilage that would normally signal their presence. This is why it is important to adhere to safety rules when using sous-vide.

Organization:

Vacuum-packed pre-portioned foods are neat, sanitary, and easy to organize. Many portions of the same product can be fabricated at the same time and then sealed, which minimizes cross-contamination. The food is handled minimally before being placed in a sterile environment. Retrieving food is easy, and each portion is individually protected from spills and other dangers, such as a raw product dripping onto a cooked product.

Sous-Vide for Effect:

Recently, the unique properties of the sous-vide process have inspired a cooking movement that aims solely to increase the quality of food and achieve special culinary effects. Think of this as sous-vide for effect.

Texture Modification (aka Compression):

The key to this technique is long vacuuming to get all the air out of the inside of the food. After the food is sealed and the vacuum released, there is an immediate observable change in the product as the voids that used to contain air are compressed. On some products, the effects of compression are accentuated over time (pears become more translucent after several hours). This process can be accelerated by re-vacuuming the sealed bag until the bag inflates with water vapor and then releasing the vacuum.

Porous foods can have their texture and appearance radically modified by vacuum-packaging. Watermelon, for instance, becomes denser, changing from a mealy to a candy-like texture. Pears, cucumbers, and tomatoes become translucent.

Flash Pickling and Vacuum Marination:

Vacuum-packaging foods increases the uptake of flavorful liquids, brines, and colors. The more porous the item, the more dramatic the end results are. For example, a pear can be colored with port in an hour under vacuum. Cucumbers and other vegetables can be flash pickled in seconds. Meats can be brined in much less time than at atmospheric pressure.

Forming :

The pressure exerted by the atmosphere can be used to form dishes. Layers of food can be pressed extremely flat. Once removed from the bag, these compressed layers become easy to slice into beautiful portions. Food can be arranged as in a terrine, vacuumed, solidified, and sliced for decorative effects. Some effects formerly achieved with a simple mold and a weight can be achieved more easily with a vacuum machine.

De-airing :

When thick sauces and purées are blended, they often have large amounts of air whipped into them. Sometimes this air is undesirable. When chefs use modern thickeners and gelling agents, like xanthan gum, trapped air becomes a problem, as it affects the body of the sauce and its appearance (liquids with many air bubbles appear white and opaque). The thicker the sauce, the more difficult it is to remove air. Sauces that contain too much air can be made crystal clear by removing the air bubbles in a vacuum machine.

Any liquid can have all their bubbles removed in a vacuum machine. Place the liquid in an appropriately wide container (not a bag) inside the vacuum machine. If there is too much liquid in the container, the mixture will boil over and create a mess during the process. Close the chamber and introduce a vacuum; the liquid will start to rise and bubble. Soon after, the initial bubbles will break and the liquid will enter a rolling boil. At this point the vacuum can be released and the liquid will have cleared. This procedure is one scenario where there is no need to pre-chill the product being vacuumed because the desired outcome is to have the product boil.

 The sous-vide crème anglaise won on both taste and texture.  The Ziploc crème anglaise had a more apparent egg taste and aroma than the sous-vide crème anglaise.  It also seemed to have a looser texture to it while the sous-vide version had a smoother, more velvety mouth-feel.

To answer why we cook our crème anglaise sous-vide, we’ve listed out both procedures for you to compare for yourselves.  We could use the traditional labor and supervision-intensive method:

1)      Scald milk & cream with vanilla and set aside
2)      Whisk together yolks & sugar until pale (blanchir)
3)      Temper milk & cream mixture into yolks & sugar
4)      Return to clean pot and heat mixture until the right nappant consistency is achieved, making sure not to scramble the yolks
5)      Strain the crème anglaise
6)      Chill the crème anglaise by stirring it in a bowl over an ice bath

Or we could cook the crème anglaise sous-vide, requiring about 5 minutes actual labor:

1)      Blend all chilled ingredients (milk, crème, vanilla, yolks, sugar, pinch of salt) at once in a Vita Prep (it’s important that all ingredients be as cold as possible in order to suck a better vacuum on the bag, i.e., contents won’t boil as quickly)
2)      Vacuum bag mixture (de-aerating it at the same time) and circulate in a water bath at 82°C for 20 minutes once it comes back up to temperature.
3)      Squeeze bag to agitate the contents while chilling it in an ice bath.

Voilà, easy crème anglaise.  You could prep that a week in advance and just keep it in the fridge.  In fact, we have actually kept a bag for longer just to see; it can last up to a month, but we recommend keeping it under a week.

Joan Roca recommends mashing the bag to agitate the contents, which we faithfully did without question, until one day Dave and Chef Hervé decided to see what would happen if we didn’t.  It turns out that if you don’t agitate the contents before it chills thoroughly, it results in a clumpy crème anglaise. It can easily be fixed after the fact by just stirring it back up, but you might as well just do it when it’s in the bag.  You don’t have to mash the contents in the hot bag and burn your hands (which we also used to do) either.  Instead, you can just dunk it in ice water and mash the bag while submerged, but before it’s cool.

Thomas Keller’s recipe says to put the bag in a circulated bath at 85°C and then drop the temperature down to 82°C. Unfortunately, we’ve known a lot of people who forget to lower the temperature… which means scrambled anglaise. We prefer to drop it in at 82°C and let it ride.

Nils and Dave teach three Advanced Studies courses at The FCI: Hydrocolloids, Harold McGee Lecture Series, and the first class of 2009—Sous-Vide. The two-day Sous-Vide Intensive covers the “what” and history of low temperature and sous-vide cooking (read on for more on why they’re not synonymous), and then spends the majority of the class on the “why” and “how.” True to tradition, the preparation days leading up to this class were filled with agenda re-writes, last-minute custom-building of equipment, threats of quitting, and temper tantrums… and that was just Dave. As previously stated, Nils and Dave are perfectionists who always spend the days leading up to any of their classes rethinking every detail and challenging themselves to make the class better each time.

When the class does finally hit, they always deliver. Only 16 students are allowed in Sous-Vide Intensive, so it becomes a very intimate environment. Nils & Dave prefer when their classes are open forums, with students asking questions throughout. This allows them to constantly tailor the class to the specific interests of those in the room. My favorite part of the class (and I know from speaking with past students that it enhanced their experience as well) is the Dave & Nils banter: Dave making jokes about how Nils loves to make all his food tubular; Nils sarcastically saying “nice job” if/when Dave explodes something; both of them going off on tirades about which foods and equipment bother them, like canned tuna and digital ovens; or the true origins of Porcini mushrooms.

Dave & Nils don’t teach this class out of obligation—they truly love low temperature cooking. Each of them personally owns a PolyScience circulator (about $950) and together have led The FCI to purchase five. Once upon a time, some of the chefs at our school had never used a circulator and were skeptical about doing so. A year ago, we could have all seven circulators to ourselves for days and no one would care. Now, we can barely get our hands on three at a time and within hours, someone comes to us to borrow one. Dave laughs, “The same guys who used to give me crap about using a circulator now give me crap for hogging them! Circulators are like potato chips. You get one and you want more. Once it becomes an option, you’ll use it all the time.”

Compare our current class to past classes and you can see how prevalent low-temperature cooking is becoming in the industry. Before, many students had heard of, but had no experience with, Sous-Vide. In this last class, every single student either had experience doing low temperature cooking, access to a circulator or some form of steam oven at work, and a few of them even owned their own personal vacuums, circulators and/or combi ovens!

In class, Dave starts out with an intro covering the history—development of sous-vide in 1960s Sweden and the frenemies of sous-vide cooking: George Pralus (worked with the Troisgros brothers cooking foie gras in plastic pouches and serving it in high-end restaurants) and Bruno Goussault (who worked with Joël Robuchon and French railway company SNCF). After another 15 minutes or so of back story, Dave promises to wrap up the segment shortly, “Almost done with this, I swear to God…” he mutters under his breath, gauging both the students’ and his impatience to move on to discussions and demos on the “why and “how.”

He starts with the Egg Series, his classic method of showing what low-temperature, 0— ΔT cooking means. In traditional cooking, you heat the instrument you cook with to higher than the final temperature you want the object you’re cooking to achieve. That difference between, let’s say, the oven’s temperature and the chicken’s final temperature (T) is the Δ (delta/difference). The immersion circulator allows us to cook without that difference by constantly regulating the temperature of a water bath (a much better heat conductor than dry oven air or oil/fat) by circulating it through a heating coil attached to a thermal couple. Simply set the circulator temperature to the end temperature of what you are cooking.

Egg Series

Dave cracks out eggs that have been cooked by circulated bath for an hour set at varying temperatures, ranging from 57°C (basically raw) to 70°C (hard-boiled, right before it gets that green ring around the yolk). As he moves up the temperature range, students begin to understand how each degree change in temperature makes a difference. He cracks out perfectly poached 62°C eggs and then shows his favorite 63°C “custard egg”—so named because of the creamy consistency of the yolk, which cannot be achieved with conventional cooking. Yolks at 64-66°C have a playdough consistency. (Dave suggests molding a playdough yolk into a small animal figurine for your next plating… Maybe not.)

The Egg Series demo is the “ah ha!” moment for most people. As Dave cracks out several 62°C eggs, perfect Eggs Benedict or toast-poached eggs, you start to see service-related benefits. No more simmering whirlpool with a drop of vinegar in it. The only limit on how many eggs you can cook at once is how many you can fit into your bath comfortably. During service, you can plate as soon as you can crack open the egg. And that’s just for eggs…

The class speeds on from there and students are able to see the affects of low-temperature and sous-vide cooking on different types and cuts of proteins. Someone once asked me which I preferred: a sous-vided short rib or a slow braised short rib. If you have to ask that question, then you have obviously never had a two-day, sous-vided 57°C short rib! It’s the difference between dry well-done meat and a beautifully tender, juicy, medium-rare bite of short rib. That’s the beauty—the sous-vided shortrib is cooked for two days, dissolving tough connective tissue, yet can still be served medium rare. In the class, students get to see and taste the difference. Nils serves up Swedish Meatballs composed of ground beef, pork and lamb that have been flash-fried in beef fat, packed in beef fat in a ziplock bag with as much air removed as possible, and circulated. Once out of the bag, they are flash-fried in beef fat one more time. At first, I wasn’t sure how I felt about the perfect, tender texture and juiciness of the sous-vided meatball. Then, I tasted a traditional meatball expecting to prefer its harder, denser texture. Still delicious, but now I know what I’m missing…

Class also includes a primer on Transglutaminase, or meat glue as it’s affectionately nicknamed by chefs. No, it’s not glue, but an enzyme that bonds proteins together. To quote Dave, you can use it to “glue chicken to cow to pig to donkey to horse to fish to scallop to anything.” (Please don’t post comments on animal cruelty; we’re not gluing donkeys to horses—I promise.) Nils continues, “You can glue chicken to salmon if you wanted, but it’s the worst idea in the world.” To demonstrate what a good transglutaminase idea is, they glued chicken skin to skirt steak and then deep-fried it to make the best damn Chicken-Fried Steak that you’ll ever have. The class is also lucky enough to get a lesson on rolling chicken or salmon into tubes from the tube expert himself, Nils. Tubes allow for perfect portioning (discs of equal weight and size) of whatever protein you’re cooking.

“The sitting portion of this class is now over!” Dave commands in order to get everyone out of his or her seat to get a closer look at the vacuum. Dave explains the vacuum chamber and how pressure and air are removed, then reintroduced, and what affect that has on what’s inside the chamber, i.e., porous items in a liquid bath or bag or whatever else. Students get to witness texture modification and vacuum infusion, and see elements of that afternoon’s dishes and cocktails being prepared. Apple cubes are placed in a container of chilled, bright yellow curry-infused oil and vacuumed. Students watch as air from tiny pores within the apple escape out of the chilled oil, bubbling its surface. The apples are allowed to sit under vacuum until it appears that most of the air has escaped, i.e. the bubbles have stopped. When air and pressure are reintroduced into the chamber, the curry oil is forced into the empty voids in the apple created by the vacuum, and the cubes become bright yellow and translucent.

Pressure cookers (aptly named) are another great example of how pressure is used in cooking. We used it to trigger the alkaline reaction in Hamine Eggs in about 30 minutes, not the traditional preparation which requires eggs to sit overnight. Our eggs are then used to turn a classic into a modern masterpiece: Deviled Hamine Eggs. I can take down a whole tray of these treats, but luckily there are never that many left over for me to do so.

As always with a Nils and Dave class, a cocktail is served at the end of class… and it’s always served in a liquid nitrogen-chilled glass (have liquid nitrogen, will use). It’s a reward to students and staff alike for making it to the end of an information-packed day. It’s not a bad way to help wash down an afternoon’s worth of meat tasting, either. Delicious, infused, carbonated liquors garnished with texture modified fruits (or flash-pickled watermelon rinds—my favorite), also seem to be a great way to coax students into asking questions that may have not come up yet during the class.

I can’t stress enough that the best part of this—and all of Nils and Dave’s classes—is the interactive environment. I’ve been asked so many times what it’s like to work closely with Nils and Dave—this is probably one of the best ways to get that experience yourself. There’s no better opportunity to observe how they work, what their thought process is, or to ask them questions about your own cooking techniques. The goal of the class is to provide the foundation necessary to start using low temperature and sous-vide (if you are HACCP-ly able) techniques on your own. Nils and Dave try and stay as long as possible to answer any lingering questions, especially since questions emailed to Dave later “might as well be sent to a trash can.” He would love to be able to answer them, but email is just one of those things our resident-genius can’t seem to get a handle on.

Of course the only real way to experience this class is to actually take it! Luckily, the Sous-Vide Intensive class is being taught again on May 28th & 29th. The class is limited to 16 participants, so if you are interested in taking the class, I highly recommend that you contact the school to reserve your place as soon as possible. For information about this class and all of Food Technology classes offered, please visit our Advanced Studies page.