My immersion circulator is working again! And the first thing I decided to do was to cook eggs at 63.0 °C for 40, 60, 75, 110 and 155 min and show you the results. If you read my last blog post on Perfect egg yolks or have stumbled across the paper Culinary Biophysics: on the Nature of the 6X°C Egg you may recognize that these times correspond to egg yolks with textures similar to sweetened condensed milk, mayonnaise, honey, cookie icing and Marmite respectively. I used the iso-viscosity graph from the paper mentioned to determine the cooking times as shown below.

The figure shows how cooking times at 63.0 °C are determined to achieve different textures. (The figure is used with kind permission from Springer Science+Business Media: César Vega and Ruben Mercadé-Prieto in Food Biophysics 2011, 6:152-159, Culinary Biophysics: on the Nature of the 6X °C Egg, figure 8, page 158. The legend overlay has been added by me for clarity.)

As the individual eggs reached their cooking times they were held in cold water until the last egg was finished. I then cracked all the eggs and took the pictures below to illustrate the differences in textures. I think the picture speaks for itself. The amazing thing is that the only difference between the eggs is the cooking time!

It can be difficult to judge textures properly from still photos, so I also shot a few video clips to illustrate the texture of the 40, 75 and 155 min eggs (by the time I shot the videos the yolks had become more viscous, possibly due to cooling and/or evaporation). The texture ofthe 155 min egg yolk was perhaps the most fascinating with a tremendous plasticity. There must be some exciting culinary uses for this!

If an egg is to be served by itself one will typically also want to set the white. There was a question about this to my previous post, and a reader even tried with 2 min pre- or post-boil. Without cooling the difference between pre- and post-boil was quite significant as evidenced from the pictures. I did a similar experiment but cooked the eggs at 63.0 °C and opted for a 3 min pre- or post-boil with the small difference that I cooled the egg back to room temperature after/prior to the pre-/post-boil to avoid any interference between the 63 °C and 100 °C treatments. This worked very well and I wasn’t able to detect any difference between the pre- and post-boiled eggs.

It doesn’t matter if you pre- or post-boil your egg as long as you cool it to room temperature inbetween the boiling water and the temperature controlled water bath.

Bruno Goussault started the sous vide master class at The Flemish Primitives 2011 by arguing that precise temperature or right temperature cooking is a better term than low temperature cooking. It’s really about knowing at which temperature the desired change takes place (or even better: knowing which time-temperature combinations will yield the desired results – this is a topic I will come back to soon).

Recounting the early days of sous vide, Bruno Goussault explained how he was once asked about how to produce prepare tender meat from a though cut. He was aware of a science paper on a slow cooking technique from USA (anyone know which paper this was?). It utilized a water bath, but the water washed away the juices. To avoid this Bruno wrapped the meat in cling film. A roast beef cooked at 58 °C turned out tender with a nice pink color. Then a friend working with plastics suggested that he should look into polyethylene (PE) bags in combination with a sous vide machine (boil-in-bag had already been around for some time apparently). Interestingly Bruno mentioned that during a recent Bocuse d’Or competition in USA where Bruno trained the American team, they replaced the plastic with a “skin” made from shrimps. Maybe we will see more “edible” skins used in sous vide in the future?

VACUUMING
Bruno then went on to talk about the vacuuming process and how time/pressure profiles should be adjusted to respect the shape and properties of the product, in particular when working with fish. A challenge with vegetables is the enzymatic release of ethylene, causing the bags to inflate (resulting in a poor heat conduction). The advice for vegetables and potatoes: use maximuum vacuum. But if you use the same setting for poultry the bones will turn out black because you extract bone marrow through the bones. Thus the vacuum should be sufficient to extract air from the bones, but not so high that the marrow is extracted.

Vacuum packing turns out to be a great way to impregnate food with flavors. As an example Sang-Hoon Degeimbre prepared oysters impregnated with champagne, cooked for 5 min at 83 °C and served with kiwi extract and an oyster leaf, Mertensia maritimia (Thanks Arielle!).

COLOR
When working with vegetables it is always the chlorophyll which causes problems (not the red/orange carotenes or the red/blue/purple anthocyans). This is due to the loss of the central magnesium ion. The easiest way to prevent this is by raising the pH. This can be done with baking soda (sodium bicarbonate), but gives an awful taste according to Bruno (and personally I would add that bicarbonate easily gives a mushy texture as well). A more advanced way to preserve the bright green color would be to add some other alkalizing/buffering agent such as sodium triphosphate (aka as sodium polyphosphate) or sodium hexametaphosphate (if you’re really interested, check out the paper Effect of pH on chlorophyll degradation and colour loss in blanched green peas for instance). And while we’re discussing color:  a side effect of the vacuum packaging of vegetables is that the air cells collaps, thereby reducing the diffraction of light which results in a darker and more intense green color.

Sang-Hoon Degeimbre shows how vacuuming gives greens a darker green color

STEPWISE COOLING
In restaurants sous vide is often used in a cook-chill-reheat fashion. For such a setup Bruno argued that it is vital to cool the meat or fish stepwise to allow a readsorption of the exudated juices (which also dissolve/carry away spices and Maillard products on the surface). If plunged directly into ice water fat and gelatin can cause the juices to gel, thereby effectively preventing a readsorption of the liquid. By taking the temperature down in a more controlled way the water holding capacity of fish/meat is improved and a portion of the exudated juice will be readsorbed (together with the flavors from the surface). A suggested stepwise cooling protocol for fish could be as follows: 10 min at room temperature, 10 min in cold water followed by 2 h in ice water. And it’s even possible to elaborate further on this – Bruno mentioned that he had developed a 4 step SV procedure followed by a 3 step chilling for Joel Robuchon. To me this also suggests that meat which is inteded for immediate serving should also rest a couple of minutes in the presence of the exudated juices. Would be interesting to know more about which factors influence this readsorption actually (maybe an interesting topic of a masters/PhD project?).

FISH
When preparing fish it is recommended to allow the fish to soak in a 5% brine for 10 min (Bruno lived for 3 years in Stavanger in Norway, and learnt this from a Norwegian chef during his stay – unfortunately he could not remember his name). This increases the osmotic pressure in the cells and prevents albumin from escaping (think of baked salmon with lot’s of white albumin leaking out) according to Bruno. After brining the recommended cooking times for a fish filet is then 1-3 min at 83 °C for pasteurization followed by 5 min at 58 °C for finishing.

Water baths set at 58, 66 and 83 °C. For a restaurant with only three water baths these are the recommended compromise temperatures.

TEMPERATURE
The many recommended temperature settings for meats and fish can be a challenge in a restaurant setting with a limited number of water baths. Bruno’s simplified approach was therefore to have three water baths at the following temperatures:

• 58 °C (and in any case below 62 °C): At 56 °C albumin is sill runny, at 58 °C it begins to whiten (and the overall color of meat is actually a result of seeing the red meat color through a white “fog” of albumin covering the muscle fibres. This temperature is recommended for fish and meat that is to be served red.
• 66 °C (in any case below 68 °C): The water holding capacity of the muscle tissue is dramatically reduced when heated above 68 °C. A temperature of 66 °C is therefore appropriate to retain the juiciness of meat. This temperature is recommended for poultry and well done meat.
• 83 °C (in any case below 85 °C): This temperature is suitable for vegetables as they need a temperature above 80 °C to be properly cooked, but at 85 °C pectin begins to hydrolyze so it’s important to stay below that temperature. This temperature is also suitable for a quick pasteurization of the surface of fish and meat.

Potatoes cooked for 3.5 h at 83 °C turn out really delicious.

HYDROLYSIS OF CONNECTIVE TISSUE
The hydrolysis of connective tissue was also briefly mentioned. For a though cut of meat such as shoulder or top blade 4 h at 100 °C are needed to break down the connective tissue. At 66 °C the same process takes 76 h, and further lowering the temperature to 56 °C will require a full 120 h for the similar break down of the connective tissue. But in return the low temperature gives a meat with a very nice color. Interestingly, Bruno mentioned that due to different aging practices a similar cut in the USA typically would only require 72h at 56 °C to reach the same tenderness! So the time/temperature combinations should only be used as rough guides.

Lamb cooked for 36h at 66 °C has a very nice texture!

Other tips & tricks:

• Rabbit and game are difficult to cook sous vide: sugar/glycogen in the muscles is converted into lactic acid which inhibits the cooking process (does anyone have more background information on this?)
• The boling point of water at 10 mbar is 6.9 °C. This is the reason why everything you plan to vacuum pack at this temperature should be cooled to below 6 °C, otherwise the liquid will start to boil in the vacuum.
• Regardless of what is cooked Bruno recommended a quick dip into a 83 °C water bath for pasteurization.
• It is better to generate Maillard flavors before sous vide cooking: the flavors will dissolve in the exudated meat juices and then be readsorbed by applying a proper stepwise cooling. If desired a short browning can be applied after sous vide cooking for crisping of the surface.

A very engaged Bruno sharing his knowledge about sous vide cooking

At the end of the session I got to chat a little with Bruno. He said that he was very happy about the wide spread use of sous vide, but also emphasized that it is a technique that can amplify mistakes as well as successes. -Many chefs don’t respect the temperature recommendations! I visited a chef who cooked meat at 54 °C and it smelled terrible, Bruno told me. The different bacterias can greatly influence the flavor of the resulting product if care is not taken to eliminate them. I asked Bruno about low temperature/long time combinations, but he said that chefs generally are not patient enough. They already complain that they don’t have time for the long sous vide preparations. Bruno does a lot of sous vide consulting for chefs and restaurants (in France/Europe through CREA founded by him in 1991 and in the US as a consultant for Cuisine solutions), but does not have big hopes for sous vide in home cooking: - No, it’s a gadget! Sous vide works best for cook & chill in a restaurant setting.

Thomas Bühner explaining how his “raw” meat jus is prepared. In the background the minced meat is being prepared.

(RAW) MEAT JUS
In the last part of the master class the German chef Thomas Bühner (La Vie, Osnabrück) demonstrated the preparation of meat jus (i.e. the natural juice given of by meat when heated). Ground meat was vacuumed and cooked for 2.5 h at 56 °C. The meat juice was then collected using a chinois and further concentrated using a rotary evaporator operated at 120 mbar and a water bath temperature of 40-50 °C (important to keep the water below the temperature of the sous vide water bath in order to retain the raw meat flavor). Compared to a conventional cleared stock the reddish meat jus is opaque. The meat jus is devoid of Maillard flavors due to the low temperature used, and this ensures a raw and bloody taste. The taste was interesting I would say, but perhaps not very delicious on it’s own … But I’m curious how it’s actually incorporated in his restaurant.

Conventional stock (left) and evaporated meat jus (right)

Thomas Bühner also demonstrated vacuum infusion using the Gastrovac. Potatoes were pierced/scorched, submerged in the truffle jus and then placed in the vacuum of the gastrovac. Thomas then repeatedly let air into the Gastrovac to allow cells to collapse and improve the impregnation.

When I wrote about Nathan Myhrvold’s book project in November he estimated the book to reach 1500 pages. But what originally started out as a 300-page book on sous vide has now, with the help of a 20-person team, grown to a total of 2200 pages spanning five volumes! Need I say more? Finally the long wait is over: The Modernist Cuisine: The Art and Science of Cooking is now available for pre-order at Amazon, and the expected release date is December 1st. One could almost be afraid that there will not be anything more to blog about here at Khymos as everything will be covered in Modernist Cuisine (but I know better – every previous talk about “end of science” has turned out to be more a starting point than a final destination)

Ferran Adrià says that “This book will change the way we understand the kitchen”, and according to Heston Blumenthal it’s “A fascinating overview of the techniques of modern gastronomy”. And if that’s not enough – take a look at this 26 minute video which guides you through the almost endless amount of high-tech equipment Nathan Myhrvold and his team have available. Oh boy, oh boy!

Other links:
The lecture “Cooking in Silico: Understanding heat transfer in the modern kitchen” by Nathan Myhrvold and Chris Young is available for streaming/download from University of Washington.

Nathan Myhrvold giving a TED talk about some of his many interest (click image to see video). Photo by Neil Hunt from flickr.com (CC BY-NC 2.0).

If you’ve played around with sous vide cooking there’s a good chance that you’ve visited the massive eGullet thread on sous vide (currently spanning more than 100 pages and 3000 posts), and in that case you’ll be familiar with Nathan’s many well informed posts on sous vide. There have been rumours about an upcoming book for quite some time, and things are getting more and more exciting. The last I heard was that he had a team of 5 people working on a book about sous-vide. This has now increased to a team of 15 people, including 5 professional chefs, a photographer, an art director, writers and editors. And there’s more:

“The project has grown in size and scope. Originally planned as a 300-page discussion of sous vide, an increasingly popular restaurant technique of cooking food in vacuum-sealed bags in warm water baths, the book has swelled to 1,500 pages that will also cover microbiology, food safety, the physics of heat transfer on the stove and in the oven, formulas for turning fruit and vegetable juices into gels, and more.”

Wow! Let’s hope that Nathan’s “one year left” statement is actually true this time. I’m really looking forward to see this book!

Many cookbooks suggest the following for boiling eggs: 3-6 min for a soft yolk, 6-8 min for a medium soft yolk and 8-10 min for a hard yolk. If you are satisfied with this, there is no need for you to continue reading. But if you’ve ever wondered whether the size of an egg has any impact on the cooking time you should read on. And if you search the ultimate soft boiled egg we share a common goal! From a scientific view point, a cooking time of approximately 3-8 minutes to obtain a soft yolk is not very precise. A number of important parameters remain unanswered: What size are the eggs? Are they taken from the fridge or are they room tempered? Are they put into cold or boiling water? And if using cold water – when should the timer be started? When the heat is turned on or when the water boils? And would the size of the pan, the amount of water and the power of the stove top matter?

A formula for boiling eggs?

I still remember the very first time I heard about a formula to calculate the cooking time for eggs. I was in high school and as a recipe for the ultimate nerd the egg formula gave me a good laugh. Now – many years later – I count myself to this group of nerds And thanks to the internet, google and Peter Barham’s book “The Science of Cooking” – I have been able to find out much more. I haven’t been able to track down the formula I heard mentioned, but the best documented formula nowadays is derived by Dr. Charles D. H. Williams, a lecturer in physics at University of Exeter. He has set up a nice page on the science of boiling eggs and there’s even a pdf with the full derivation of the formula. Given the starting temperature of the egg T_egg, the temperature of the water T_water and the desired temperature T_yolk (all in °C) at the yolk-white boundary, the cooking time t (in minutes) of an egg with mass M (in grams) is given by:

Whenever possible one should use weight measurements in the kitchen, but some times an accurate balance is not available and in those cases we can turn to the Peter Barham’s formula which is published in “The science of cooking”. The circumference of an egg is easily measured around the thick end using a piece of string and a ruler. I used to have a piece of string with three knots at 13, 14 and 15 cm respectively to make it even simpler. The cooking time t (in minutes) for an egg with a circumference c (in centimeters) is given by:

Former colleagues of mine at the University of Oslo have made a nice flash animation to do calculations with Barham’s formula if you’re not too keen to dig out your calculator. Barham states that his formula gives the time for the centre of the yolk to reach the temperature T_yolk whereas Williams mention in the derivation of the formula that it calculates the time for the yolk-white boundary to reach T_yolk. I’m not able to tell whether the formulas actually differ in this respect or not (comments are welcome on this issue!). A comparison of the two formulas for a set of 50 eggs which I weighed and measured shows that for T_yolk = 63 °C and T_water = 100 °C they are quite similar, except for the larger spread of the circumference measurements (see plot below). For higher T_yolk or lower T_water Williams’ formula consistently gives longer cooking times than Barham’s formula. It remains to be seen which of the formulas will be closer to the truth.

The graph shows the cooking time for 50 eggs (sorted by increasing mass) calculated from the mass and circumference using the two formulas shown above with T_yolk = 63 °C, T_water = 100 °C and T_egg = 4 °C. For the given conditions the two formulas give similar results. The most striking lesson learnt is that measuring the circumference is in fact not very accurate, hence the larger spread of these points.

The doneness of the egg depends on the temperature of the white and the yolk. Egg white starts to coagulate in the range 62-65 °C. At these temperatures it is the most heat sensitive protein, the ovotransferrin, which constitutes 12% of the egg white, which coagulates. The major protein of egg white, ovalbumin, makes up 54% of the white and doesn’t coagulate until the temperature reaches 80 °C. The yolk begins to thicken around 65 °C and sets around 70 °C. Further heating to around 80-90 °C produces the crumbly texture typical of hard boiled eggs. Many of these changes are nicely illustrated in the picture of sous vide cooked eggs below, but the changes are also summed up in the following table:

At sea level, the temperature of boiling water is 100 °C. At higher altitudes, the boiling is lowered. As a rule of thumb, the boiling temperature of water is lowered 0.3 °C for each additional 100 m above sea level. For an accurate calculation, check out his calculator. As we shall see later, the formula can of course also be used prepare eggs at sea level, using water kept at temperatures less than 100 °C. Lastly we must know the starting temperature of the egg which will typically be 4 or 20 °C.

Based on T_water = 100 °C, T_egg = 4 °C and T_yolk = 63-67 °C I’ve prepared plots for the range of 50 eggs used in the previous graph. If the circumference or mass of an egg is known, the boiling time in minutes can easily be determined from the graphs. I’ve also prepared downloadable pdfs with the circumference and mass plots.

Cooking time for eggs with given circumference or mass to reach to reach 63, 65 and 67 °C respectively at the yolk-white boundary with T_water = 100 °C and T_egg = 4 °C (click for larger image or download pdfs with circumference and mass plots)

But is this the perfect egg?

No actually not… keep reading! The problem with using boiling water is that while you do heat the yolk to the desired temperature, you have virtually no control with the temperature of the white. If your water holds 95-100 °C, so will the white (or at least the outer most part of the white). This gives it a firm, rubbery texture. So the problem is, to put it differently, that we want to heat the yolk to somewhere above 65 °C, but we do not want to heat the white above 80 °C. The solution to this problem is to “boil” the egg at a temperature lower than 100 °C, which means not to boil it at all but rather sous vide it! Eggs are perfect for sous vide because you can just drop them into the water bath as they are. No plastic bags or vacuum packaging are required. Douglas Baldwin has cooked eggs sous vide for 75 min at different temperatures ranging from 57.8 to 66.7 °C as shown below. Notice how the egg whites and egg yolks change at the different temperatures.

Composite image of eggs cooked sous vide for 75 min at the indicated temperatures (Photo: Douglas Baldwin. Picture used with permission.)

The surprising thing with some of the sous vide eggs is that they are inverted (or opposite boiled). The white is still runny while the yolk is set. If you would like to try this but don’t have a thermostated water bath for sous vide you can improvise a little. The thermostat most people do have in their kitchen is the baking oven (at least those with electric stoves). Preheat your oven to 70 °C. Then heat 1 L of water to 65-70 °C, put the eggs in, cover with a lid and leave the pan in the oven for one hour. The tricky thing here is that oven thermometers are notoriously wrong so use a separate handheld thermometer to check your oven. With some trial and error you should be able to obtain an inverted egg with a runny white and a yolk that has set.

Although scientifically amusing the inverted egg isn’t really desirable form a culinary viewpoint – the white is a little to runny. Regrettably the formulas presented above aren’t of much help either. They fail because they only take time and not temperature into account. The perfect soft boiled egg in my opinion would have an egg white which is heated to around 70-80 °C and a yolk with temperatures ranging from 64 °C at the yolk-white boundary to about 60 °C in the center. I guess it would be possible to prepare such eggs in a sous vide water bath held at 75-80 °C in less than an hour. A further complication of cooking eggs in real life is that they continue to cook when removed from the hot water. Normally this is alleviated by shocking the eggs in cold water, but if cooked at a lower temperature this could possibly be omitted. I will start experimenting to find a perfect mass-time-temperature combination with a time window that’s as large as possible, and I’ll report the results in a future blog post. And these experiments will also include a test of the recipe for eggs cocotte by Joël Robuchon, found via Chubby Hubby’s post on slow-cooking an egg.

Exotic soft boiled eggs

In his book “Off on a comet”, science fiction author Jules Verne shows that he was actually aware of the possibility of “boiling” eggs at a temperature lower than 100 °C. He has correctly observed that water boils at lower temperature in high altitudes, and that on a fictional comet of appropriate mass, water will boil at 66 °C. The temperature is wisely chosen, because by keeping eggs at 66 °C, you really can’t do anything wrong. From the last paragraph of the excerpt it seems that the eggs were not fully cooked after “a good quarter of an hour”. Of course, there is also no mention about the size of the eggs, so any further speculations end here. But I’ll rather leave it to you to read the excerpt from the Gutenberg e-text version – it’s quite amusing:

The skillet was duly set upon the stove, and Ben Zoof was prepared to wait awhile for the water to boil. Taking up the eggs, he was surprised to notice that they hardly weighed more than they would if they had been mere shells; but he was still more surprised when he saw that before the water had been two minutes over the fire it was at full boil.

“By jingo!” he exclaimed, “a precious hot fire!”

Servadac reflected. “It cannot be that the fire is hotter,” he said, “the peculiarity must be in the water.” And taking down a centigrade thermometer, which hung upon the wall, he plunged it into the skillet. Instead of 100 degrees, the instrument registered only 66 degrees.

“Take my advice, Ben Zoof,” he said; “leave your eggs in the saucepan a good quarter of an hour.”

“Boil them hard! That will never do,” objected the orderly.

“You will not find them hard, my good fellow. Trust me, we shall be able to dip our sippets into the yolks easily enough.”

The captain was quite right in his conjecture, that this new phenomenon was caused by a diminution in the pressure of the atmosphere. Water boiling at a temperature of 66 degrees was itself an evidence that the column of air above the earth’s surface had become reduced by one-third of its altitude. The identical phenomenon would have occurred at the summit of a mountain 35,000 feet high; and had Servadac been in possession of a barometer, he would have immediately discovered the fact that only now for the first time,

as the result of experiment, revealed itself to him–a fact, moreover, which accounted for the compression of the blood-vessels which both he and Ben Zoof had experienced, as well as for the attenuation of their voices and their accelerated breathing. “And yet,” he argued with himself, “if our encampment has been projected to so great an elevation, how is it that the sea remains at its proper level?”

Once again Hector Servadac, though capable of tracing consequences, felt himself totally at a loss to comprehend their cause; hence his agitation and bewilderment!

After their prolonged immersion in the boiling water, the eggs were found to be only just sufficiently cooked; the couscous was very much in the same condition; and Ben Zoof came to the conclusion that in future he must be careful to commence his culinary operations an hour earlier. He was rejoiced at last to help his master, who, in spite of his perplexed preoccupation, seemed to have a very fair appetite for breakfast.

There is in fact no need to head off to other planets to find examples of low temperature prepared eggs. If you go to Japan you’ll find onsen tamago which litteraly translates to “hot spring eggs”. Originally baskets of eggs were lowered into hot springs, but the temperature of hot springs vary so I imagine that there were several types of onsen tamago available (does anyone happen to know the exact temperature of the hot springs used?). After cooking the egg is typically cracked into a bowl of dashi soup with mirin and soy sauce. The challenge of preparing onsen tamago eggs at home is accurate temperature control (just as with sous vide in general). One tip I found was to place the egg on top of rice that has just cooked in a rice cooker. Leave the eggs to “cook” for about one hour while the “keep warm” function of the rice cooker is turned on.

Eggs boiled in onsen (japanese: hotspring), Nagano, Japan (Photo: Miya.m. Permission: GFDL, cc-by-sa-2.1-jp).

I’ve been told that in Finland some saunas are equipped with egg racks. Depending on where the rack is placed one could probably chose between hard boiled and soft boiled eggs. But the sauna would have to be kept warm for a long time due to the slow heat transfer from the hot air. And talking about eggs and saunas: If the eggs are placed directly on the hot stones they will not only be hard boiled, but actually turn completely brown and acquire a nutty flavor. In Korea such sauna eggs are known as Maekbanseok gyeran.

Other aspects to consider when boiling eggs

An egg has somewhere between 7000 and 17000 pores, meaning that water slowly evaporates (the density decreases from 1.086 g/cm³ by 0.0017 g/cm³ daily). This is also why eggs age faster at room temperature than in the fridge. Because of the pores, eggs should not be stored next to foods with a strong smell such as onions (unless of course, you want onion flavored eggs). When boiling eggs it is not uncommon that they crack. The most obvious reason is that they are dropped into the water and hit the bottom of the pot. Another reason for cracking is the expansion of trapped air at the blunt end of the egg. This air cannot escape fast enough through the small pores. Conventional wisdom has it that piercing a small hole in the blunt end will let expanding air escape to avoid cracking. It turns out someone has actually scientifically tested this (with 1000 eggs) and their finding was that there was little cracking for fresh eggs, regardless if they were pierced or not. Piercing reduced the cracking of 5-day old eggs and totally eliminated cracking of 28-day old eggs. The authors theorize that the air pocket grows due to evaporation (meaning there is more air to expand) and that the egg shell of fresh eggs is porous but that the pores gradually become clogged upon storage. Curiously the abstract concludes with the following sentence (this was written in 1973, but it’s still quite unusual for a scientific journal):

Housewives should pierce eggs before boiling them, since if they are fresh it will do no harm and if they are stale it will prevent splitting.

We can safely assume that the advise holds true for men as well! Apart from piercing holes to avoid cracking it is possible to reduce the potential damage from cracking by addition of salt or vinegar to the water. This will help the egg white coagulate faster and thus plug any crack formed.

Picture of egg shell pore (Photo: Jim Ekstrom. Permission: Freeware for non-commercial use).

If you’ve read this far, make sure to also read how the egg yolk problem was finally solved and my follow up post with pictures and a video of egg yolk cooked at 63.0 °C for 40 to 155 minutes!

Since I got my immersion circulator in December I’ve discovered that there are two critical questions that always come up as I hold a piece of meat in my hands, ready to cook it sous vide: At what temperature should I cook this? And for how long? Despite the fact that two books were published on sous vide last fall it is the short yet comprehensive guide “A Practical Guide to Sous Vide Cooking” by Douglas Baldwin that I’ve found most useful to answer these questions. Those who have followed the eGullet thread on sous vide cooking will probably recognize Douglas Baldwin as one of the major contributors alongside Nathan Myhrvold. Out of curiosity and eager to learn more I therefore emailed Douglas and asked if he would be interested in doing an email interview.

ML: From your homepage I see that you are a PhD student in applied mathematics, how did you become interested in sous vide?

DB: I have always loved to cook. Before last January, though, I mainly cooked slow food. That is when I saw sous vide mentioned in one of Harold McGee’s NY Times articles. Wow. Cooking meat at its desired final core temperature is so obvious! As a mathematician, I kicked myself for never asking “if overcooked meat is bad, what temperature should the meat be cooked at?” A question which many mathematician would instantly answer, “just above the temperature you want it to end up at.”

A quick search of the web led me to the massive eGullet thread on sous vide cooking. While the thread contains a treasure-trove of practical information — especially Nathan Myhrvold’s posts — it left me with a lot of unanswered questions. Being an academic, I turned to the scientific literature for answers; as expected, I found many answers and many more questions.

ML: Your excellent sous vide resource, “A Practical Guide to Sous Vide Cooking” has a wealth of information. What drove you to write this article? And have you ever considered publishing it in a peer reviewed journal?

DB: Thank you. I’m very glad to hear you find my guide to be useful.

As a scientist, I am driven by two things: an insatiable curiosity to learn everything I can about a topic and the desire to freely share what I have learned with the world (so others can extend and build on what I have done). After spending hundreds of hours researching sous vide cooking and discovering how much of the information online was incorrect (and potentially dangerous), I felt compelled to write up what I had learned and post it as soon as possible. I am still actively working on my guide, and hope to complete another major revision in February.

I have not submitted my guide to a peer reviewed journal because its intended audience is chefs and foodies. Though I did ask a number of food scientists to review my guide for technical accuracy, and I was recently asked to referee a paper for the Journal of Food Science.

ML: From your viewpoint, what is the biggest advantage of sous vide over conventional cooking?

DB: Control. Precise temperature control gives incredible choice over the doneness and texture of meat, poultry and fish. Tough cuts can be made tender. Tender cuts are the same perfect doneness from edge-to-edge. Fish and light meat are moist and flavorful. Pork and poultry no longer needs to be brined to be juicy (because they can be made safe without being cooked well-done).

ML: Do you think sous vide cooking will ever become so common that the equipment will be available in regular kitchen stores? And if yes – when will that be?

DB: I don’t think sous vide cooking will ever be so common that immersion circulators will be sold next to microwave ovens. But I fully expect them to be as common as smokers in 5–10 years. Like smoking, sous vide cooking requires a little knowledge and planning — an easy request of the average Khymos reader, but a lot to ask of most consumers. This is unfortunate, because I find sous vide cooking to be convenient, energy efficient, and versatile.

ML: What kind of equipment are you using yourself at home for sous vide? And how often do you typically cook sous vide?

DB: I use a Minipack-torre MVS31 chamber vacuum sealer and a PolyScience 7306C immersion circulator for most of my sous vide cooking. I usually attach the immersion circulator to a full-size countertop food warmer with a lexan lid I made — the lid limits evaporative cooling and the food warmer speeds the (initial) heating of the water and limits heat loss from the bottom and sides of the water bath. I also have a couple Iwatani butane blowtorches, a used PolyScience immersion circulator, a couple PID controllers from Auber Instruments, a Ranco ETC temperature controller, a FoodSaver vacuum sealer, and a bunch of thermocouples and meters from ThermoWorks.

I eat food cooked sous vide almost everyday. As a single guy, I batch cook most my meat in single servings pouches, rapidly chill and then freeze them until needed. While this `cook-freeze’ sous vide is very convenient, the freezing and reheating of the meat does causes small, but noticeable, degradation in taste and texture.

ML: Have you compared DIY bagging with zip-lock bags, food saver bags and vacuum chamber packs? I know that liquids are challenging with the food saver, but does the bagging method affect flavor (or even texture)? Does the small amount of oxygen in the DIY version have any effect?

DB: For meat, different bagging methods have little or no effect on flavor and texture. The primary purpose of bagging is to allow the efficient transfer of heat from the water (or steam) to the food (while still keeping the food and water separated). Sealing the food in a bag has the added benefit of preventing evaporative losses of flavor volatiles and moisture. Even when using a chamber vacuum sealer, the majority of bags have high levels of residual oxygen. The main difference between using a zip-lock bag and a chamber vacuum sealer is the extent to which the bags balloon when heated; (when heated over about 65C/150F) both bags will start to balloon because of the vapor pressure of the liquid in the bag, but the zip-lock bag will balloon more because the residual air in the bag will also expand. It is important that the food is kept from floating to the surface of the water to prevent uneven heating.

While meat can easily be cooked in a zip-lock or food saver bag, fruit and vegetable compression requires a chamber vacuum sealer. Moreover, zip-lock and food saver bagged vegetables balloon excessively in the 85C/185F water bath they are (typically) cooked in because it very difficult to remove all the air in the bag.

Liquid in the bag is indeed problematic when using a food saver, but is easily solved by freezing the liquids before bagging. (Although, I might add that freezing often traps air bubbles in the liquid which cause the bag to balloon more than it would have if a chamber vacuum sealer was used.)

ML: What are your favorites cuts of meat for sous vide?

DB: With the faltering global economy in mind, I love showing off sous vide cooking’s ability to transform inexpensive cuts of meat into something amazing. Consider the humble chuck roast, a flavorful cut of beef which is usually relegated to stews and hamburger because of its abundant connective tissue. Vacuum sealing, cooking for 24 hours at 55C/131F, and searing to a beautiful mahogany color transforms this humble cut into something akin to prime-rib! Pork shoulder vacuum sealed with lard and cooked for 24 hours at 68C/155C, torn into bite-sized hunks and fried in a little oil is always a hit at my dinner parties. Even the the lowly chicken breast can be made into something moist and flavorful by pasteurized in a 60C/140F water bath (see my guide for pasteurization times).

ML: Is there any meat that you would prefer not to cook sous vide?

DB: I don’t like some types of fish cooked sous vide. When cooked too slowly, the enzymes in the fish remain active and cause the flesh to become mushy. [This can be mitigated by using a water bath temperature 5--10C/10--20F higher than the desired final core temperature and using a needle temperature probe inserted through closed-cell foam tape to determine when the fish is done heating.] Also, fish which is not extremely fresh will taste too fishy because the flavor volatiles remain sealed in the bag with the fish —this is a particularly irksome problem for me in land-locked Colorado.

ML: Some critics claim that with sous vide, even though you brown the surface, you loose some flavor since temperature is kept so low (I believe this applies especially for pork). Do you share this experience?

DB: It is a very reasonable concern, but can be mitigated by quickly searing the meat before vacuum sealing and cooking. While the initial Maillard reaction occurs noticeably above 150–180C/300–350F, many of the subsequent reactions can occur at the low temperatures used in sous vide cooking. Personally, I feel searing after cooking is sufficient and almost never take the time to pre-sear my meat.

ML: From your experience, what is most difficult to achieve when cooking sous vide?

DB: A great sear without overcooking the meat. While a blowtorch works wonders on beef and (most) pork, it tends to burn poultry. A pan with a little oil over medium heat (so the oil is between 150–180C/300–350F) works fairly well for poultry, but may overcook the meat before the surface is golden brown.

ML: With Keller’s recent book “Under pressure” and your guide (and an extremely long thread at eGullet) being available now: Which areas would you say need further exploration?

DB: Sous vide cooking is still relatively young and there are hundreds of interesting questions yet to be answered! Some of the questions I’m currently interested in are: How long does it take all the soluble collagen to unfold into gelatin at 55–65C/130F–150F? What is the role of enzymes when cooking at low temperatures for long times? Is it better to thaw the meat or cook it from frozen? If cooking from frozen, how long does it take to heat a piece of meat (such as foie gras) stored at -80C/-110F? Which foods can be frozen or refrigerated after cooking (and for how long?) without significantly degrading taste or texture? How and why should fruits and vegetables be cooked sous vide? Why does fish retain so many more of their essential fatty acids when cooked sous vide (compared with conventional cooking methods)? . . .

In addition to the many unanswered questions, there are also many topics which are understood but have yet to be discussed in sufficient detail. For example, many people’s intuition about clamp and chamber vacuum sealers is wrong. The importance of food shape in predicting heating times has not been discussed — spherical and cylindrical foods heat much faster than slab shaped food. The relatively fast onset of warmed-over-flavor after the food is removed from its vacuum pouch is absent. And even how large and powerful the water bath needs to be for a given quantity of food has not been discussed.

Hopefully I, Nathan Myhrvold, or someone else will have the time and resources to answer all these interesting questions.

ML: Thank you very much!

Thomas Keller, known from the French Laundry, Bouchon and per se, has written the book “Under Pressure – Cooking Sous Vide” (the Under Pressure title was also used by NY Times in a 2005 feature article on sous vide). According to the publisher, Keller and his chefs de cuisine have blazed the trail to perfection through years of trial and error and they show the way in this collection of never-before-published recipes from his landmark restaurants.

The book “Sous-Vide Garen im Vakuum” (Sous vide cooking under vacuum) by Viktor Stampfer (known from the Ritz-Carlton in Dubai) has received much less attention, but certainly deserves to mentioned. The title is in German, but do not despair – it seems to be a bilingual edition with German and English text (can anyone confirm this?), but so far it’s only available for preorder from the German Amazon. According to the publisher the book gives an introduction to the equipment used including sealing devices and recommended temperatures for cooking together with numerous recipes.

These are not the first books to appear on sous vide – enthusiasts have probably obtained one or more of the books by Roca, Farber, Ghazala, Leadbetter, Choain/Noël and Calmejane/Barrier – but I’m quite sure that the new books will complement these very nicely, and they will certainly be more available as several of the others have unavailable for some time.

There is however an easier way to make a perfect steak! In restaurants the method has been around since the 70′s and is known under the name sous vide (fr. under vacuum, more info on history of sous vide in this NY Times article). The meat is packed in plastic bags, vacuumed and put into thermostated water baths. This equipment is not (yet?) found in the average kitchen. So here is a simple DIY procedure. You just use a normal plastic bag, leave the meat in the water bath for 30 min (or longer) and then quickly fry both sides to generate the products of the Maillard reaction. You do need a thermometer though to control the temperature of the water bath, preferably one with a dip in probe.

1. Put the meat (I used a rib eye steak for this experiment) in a thick plastic bag. Only put one or two pieces of meat in each plastic bag – this ensures a greater contact surface with the water.

2. Add any spices you like (salt and pepper always works well – for the experiment shown I used curry paste, soy sauce and chili sauce in stead), press (or suck) out the air and close the plastic bag tightly by tying a knot (or use a zip-lock bag). You don’t want any water to enter the bag!

3. Heat a pot of water to the desired temperature (or use hot tap water) and place the plastic bag with meat in the water. Cover with a lid (not shown in the picture) to reduce heat loss. If you use a large pot of water it’s easier to keep the temperature constant. Also, it’s easier to control the temperature with an induction or gas stove top than with an electric plate since there is no additional heating once you turn them off. Regarding the temperature, start with 60 °C (140 F) and experiment from there (or check this table at Wikipedia for doneness temperatures of meat). You should leave the meat in the water for at least 30 minutes – more for a thicker cut. But the good thing is you can leave it for much longer (several hours) provided the temperature does not come above 60 °C (or whatever temperature you decided on). A convenient way to keep the temperature constant for a long time is to put the pan with water into the oven and use the thermostat of the oven.

4. Heat a frying pan, add a fat of you choice, remove meat from plastic bag and brown both sides of the meat. Since you take the meat directly from the water bath it’s already at about 60 °C. Therefore the browning is very fast.

5. A temperature of 60 °C (140 F) gives the meat a pink interior. It’s succulent and juicy. The short frying gives it a nice browned crust and the chewing resistance is perfect. All in all a wonderful combination of taste, aroma, texture and mouth feel!

Note added January 2009:
Since I published this procedure the first time I’ve learnt a lot more about sous vide. The procedure above is a rather crude procedure, but it works. If the meat turns out grey you’ll need to turn the temperature somewhat down. If you’re interested in reading more about sous vide, the best discussion I know of which also includes important safety aspects is Douglas Baldwin’s “A Practical Guide to Sous Vide Cooking”.

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