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.

Pia Snitkjær’s thesis on Investigations of meat stock from a molecular gastronomy perspective can be downloaded free of charge. Part I includes an excellent introduction to molecular gastronomy, part II covers meat stocks with and without red wine.

Pia Snitkjær was the first student in the molecular gastronomy project at the University of Copenhagen to complete her studies. She defended her PhD thesis on Investigations of meat stock from a molecular gastronomy perspective in December last year, and this was also the topic of her presentation at the recent seminar on molecular gastronomy at the University of Copenhagen. Meat stock is typically prepared by boiling meat, bones, vegetables, spices and herbs, and after straining the remaining liquid it is reduced in volume by further boiling. The central question in the thesis was how the reduction affects the flavor and texture of the stock. Cookbooks only specify the concentration factor, but not the time needed to achieve this reduction.

If you’re only interested in the conclusion from a gastronomic perspective the take home message was that the reduction time has a significant impact on flavor. For more flavor you want to do a slow reduction over low heat (see illustration below). But you should not overdo it as this will result in bitter and burned flavors. A reduction time of 15-20 hours seems to be optimal. The simple explanation is that with a high power input volatiles evaporate from your stock pot before they have time to react to generate new flavors (for instance in Maillard type reactions).

Figure from Pia Snitkjær’s thesis showing the effect of the reduction time on the aroma concentration of the resulting stock (Copyright Pia Snitkjær, used with permission)

Pia’s thesis (free download, 0.7 Mb) has two parts. The first is an introduction to molecular gastronomy, and frankly this is the best introduction that I’ve read to date on molecular gastronomy! The second part covers preparation of meat stocks with and without red wine.

Pia did two sets of experiments to arrive at these conclusions. In the time experiment she prepared stocks with concentration factors (CF) ranging from 2-12 as a function of the reduction time (3-36 h). Studying the volatiles she found that they fell into three categories:

1. Decrease: 2-pentanone and 2-propanone (boiling points: 101-105 °C, 57 °C)
2. Increase up to 15-20 h followed by decrease: 1- butanol and nonanal (boiling points: 118 °C, 195 °C)
3. Increase: acetic acid and 3-methyl butanal (boiling points: 118 °C, 91-93 °C)

The boiling points illustrate that category 1 is driven off fast due to lower boiling points whereas category 2 will evaporate very slowly (and possibly only be removed through an aerosol). The last category has lower boiling points suggesting that these compounds were not present from the beginning and are only formed after an extensive reduction.

Similarily she observed the following flavor changes of the same time span:

1. Decrease: boiled meat, nutty, sweet flavor
2. Increase up to 15-20 h followed by decrease: tar, roast crust
3. Increase: bitter, burned, sour, astringent

In the power experiment she studied the effect different power inputs (corresponding to reduction time of 4-30 h) have on a stock reduced to the same concentration factor. The resulting flavor profiles were very different with a key result being that a high power input results in a rapid loss of volatiles. A slower reduction leaves more time for new flavors to develop. Further details can be found in the thesis and in the paper Flavour development during beef stock reduction [1].

Pia Snitkjær presenting her results at the recent MG seminar in Copenhagen

There was no time to go into details of her second research paper on red wine in stocks, but the results have been published: Beef stock reduction with red wine – Effects of preparation method and wine characteristics [2]. An important finding was that wine and stock should be reduced together, not separately – this diminished the astringency from the tannins, most likely due to precipitation of insoluble protein-tannin complexes (just like the ones which make Norwegian egg coffee easy to drink). Furthermore it was shown that the initial differences in the aroma profile of the wines was partly eliminated by boiling. The choice of wine however still had an impact on the resulting flavor because the non-volatiles such as sugars, acids and phenolics of a wine did influence the end result. More specifically a reduced stock made with Zinfandel had bread, herb, wine-vinegar and chicken notes whereas a reduced stock made from Cabernet Sauvignon was dominated by beef and onion odors accompanied by a “salt taste and a significantly higher intensity of particulate mouthfeel and bitter taste”.

[1] Snitkjær, P.; Frøst, M. B.; Skibsted, L. H.; Risbo, J. Food Chemistry 2010, 645. DOI: 10.1016/j.foodchem.2010.03.025

[2] Snitkjær, P.; Risbo; J.; Skibsted, L. H.; Ebeler, S.; Heymann, H.; Harmon, K.; Frøst, M. B. Food Chemistry 2011, 183. DOI: 10.1016/j.foodchem.2010.10.096

The fascinating thing about a filtration like this is that you can also remove color. At the EuroFoodChem XIV conference I was told by Jorge Ruiz of Lamaragaritaseagita that you can make perfectly clear tomato juice by succesive filtrations, starting with a coarse filter and moving to finer filters. All in all, 3-5 filtrations should be sufficient.

This month’s TGRWT is hosted by Le Petite Boulanger, and the foods to pair are chocolate and meat. The recipe for the chocolate beef stock cream is inspired by the Iberian Ham Cream by Ferran Adrià/El Bulli (the recipe can be found on p. 21 in the hydrocolloid recipe collection). I used anis because it brings out the meatiness very well. After mixing in the olive oil I saw that the droplets were not properly dispersed. Addition of some lecithin which solved this problem.

Chocolate beef stock cream
100 g water
2 g beef stock powder
10 g chocolate (70%)
1/4 t anis, powdered
0.5 g xanthan
0.2 g lecithin
20 g olive oil
honey and chili oil to taste

Heat water to dilute beef stock and melt chocolate. Cool. Add xanthan and lecithin. Mix with immersion blender. Add olive oil. Mix until smooth texture. Sprinkle with chives.

Grilled pork tenderloin
pork tenderloin, cut in 3 cm thick pieces
oil
powdered anis
crushed garlic

Marinate meat with oil, garlic and anis mixture. Grill. Serve together with the chocolate meat broth cream.

Verdict: The chocolate beef stock cream has very meaty and almost nutty flavour. Honey is important to round of the otherwise slightly bitter taste of the chocolate. Chili oil gives it a bite, but can be omitted.

You can get an impression of the texture from this video: