When a cooking method rhymes with taste, health and efficiency, it opens up countless opportunities for foodservice professionals and amateurs alike. In 12 questions and answers, this article gives you the keys to understanding and mastering sous-vide cooking at a precise temperature.
What is cooking?
The aim of "cooking" is to transform food by means of heat, modifying the functional properties of its components and thus improving its taste (aromas and flavors), texture, color, tenderness and digestibility.
The second objective of cooking is to ensure food safety and durability.
"When it comes to cooking, look for what tastes good, and you'll get what's healthy.
Bruno Goussault
What is low-temperature cooking?
Low-temperature cooking is a technique that involves cooking food at a lower temperature than traditionally used, but for a longer time, to achieve better texture and juiciness. Low-temperature cooking is usually contrasted with traditional high-temperature cooking.
What is precise-temperature cooking?
Precise-temperature cooking is a technique for cooking to a precise core temperature, achieved in several stages in environments of decreasing temperature.
What's the difference between low-temperature and precise-temperature cooking?
Low-temperature cooking is different from precise-temperature cooking, and lacks the precision and rigor of the latter. It follows current trends, using temperatures that can sometimes prove dangerous. Lower than low, you don't know where to stop: the 52°C limit, which is the starting point for the destruction of the vegetative forms of pathogenic bacteria, is little known, and this worries the food and hygiene authorities.
For meat and fish served raw or cooked below this 52°C temperature, which I call "hot sushi", the food must be used very freshly and served immediately after preparation, which is not always the case in some restaurants where dishes are prepared in advance and left to stand before being served.
Meat or fish cooked at low temperature is not necessarily interesting from a sensory point of view, as it tends to be completely soft. On the other hand, cooking at just the right temperature produces a texture with chewiness on the outside, while keeping the soft, melt-in-the-mouth texture on the inside.
What are the maximum core temperatures for preserving flavor?
Generally speaking, the taste of a food is preserved up to 66°C for animal products (meat, fish) and 83°C for vegetable products. An exception is poultry thighs, which remain juicy up to 74°C.
How to cook to the right temperature?
Water is the best heat-transfer fluid, and can easily be regulated to within 1/10th of a degree, allowing precise control of cooking temperature. Of course, we need to wrap the product we want to cook so that the water doesn't denature it, and to that end we put a second skin on it. Today, this skin is a plastic bag in which a vacuum is created to ensure that the film adheres to the product and that the heat transfer with the cooking bath is optimal. This is the basis of the vacuum cooking technique. It's a demanding technique, requiring investment in equipment, but one that offers many advantages.
What can science contribute to the art of cooking?
To achieve the desired visual and taste results, chefs and amateur cooks need to understand the functional properties of a food, and therefore what the product is useful for in their recipe. Functional properties have a direct relationship with sensory properties.
How do the functional properties of foods change during cooking? The example of the egg.
Eggs have 4 main functional properties of interest in cooking:
The transparency of egg whites:
It allows the color of other foods to be seen through it. This transparency is maintained up to 58°C. Above this temperature, the albumin is altered and white spots appear. Color perception is altered, like a "London fog"! The same phenomenon occurs with proteins present in red meat, which goes from red in the open air, to blue when cooked to medium-rare (below 62°C), to gray when cooked to well done (above 63°C).
The coagulation property of egg whites:
It enables several proteins to stick together. This "cementing" capacity begins to break down at 60°C. The rate of degradation depends on the temperature and duration of cooking.
Using egg white to glue proteins together avoids the use of transglutaminase, an additive found in surimi and certain vegan dishes, which can cause allergic reactions and is also suspected of creating an environment conducive to bacterial growth.
The foaming property of egg whites:
Egg whites can be used to create foams and lighten preparations.
This property degrades with temperature, ceasing to exist above 60°C.
The emulsifying property of egg yolk:
It is used to make sauces such as mayonnaise or Béarnaise.
This functional property degrades with temperature at around 65°C.
What are the advantages of sous-vide cooking at precise temperatures?
1. Enhanced flavor
During cooking, food loses water, and with it, flavor.
For example, when blanquette de veau is cooked in the traditional way, i.e. in boiling water at over 95°C, the meat loses its flavor, which goes into the cooking water.
If you cook it using the "precision-temperature vacuum cooking" technique, at 66°C throughout, the meat retains most of its water. The small amount of juice can then be recovered from the cooking water and used to make a roux, which will recover the flavor elements for a sauce. The roux makes use of the functional property of starch, which swells in a liquid and gels the taste elements together.
2. Enhancing the value of meat trimmings
Cooking at just the right temperature makes it possible to achieve high-quality sensory properties (texture, color, juiciness) with pieces of meat that are generally destined to be processed into minced meat, used for pet food or thrown away.
Vacuum-cooking a dish of beef ribs for 72 to 120 hours (depending on the quality of the beef) at 56°C produces taste values similar to those of the best cuts. A chef can thus offer a plate with a range of beef muscles cooked to just the right temperature (fillet, cheek, shank, etc.), reducing production costs while offering an incomparable taste experience.
3. Consistency
"Vacuum cooking is to cooking what cinema is to theater! It's reproducible and delivers the same performance every time, making it easier to achieve the desired result and improve food cost management.
4. Preservation
Very good results are obtained when food cooked at just the right temperature under vacuum is stored in its cooking bag in cold storage at 1-3°C, in order to preserve its pasteurization. I hope to be able to show that carrots cooked at 83°C can be stored for up to 1 year without losing their taste.
5. Food safety
Compared to low-temperature cooking, this is essential for food safety, as it helps kill harmful bacteria and parasites that can cause food poisoning. Very precise time and temperature conditions must be respected. The sous vide technique avoids the risk of contamination during storage after cooking, since the food can be kept in its cooking bag, unopened, until use.
6. Nutrient preservation
It can help preserve food nutrients thanks to its conservation bag, which stops the dilution of vitamins and minerals in cooking water or fat. What's more, while high temperatures often result in considerable vitamin destruction, reducing the nutritional value of food, cooking at just the right temperature is less harsh on the product.
However, degradation is a function not only of temperature, but also of nutrient type and cooking time. Researchers have shown that there are cases where high-temperature cooking preserves more nutrients.
7. Innovation
Precise-temperature cooking provides innovative solutions to the constraints of professional kitchens.
For example, as cooking at just the right temperature is slow and precise, an innovative solution to optimize the use of infrastructure is to cook at night, or between services, without requiring a chef to be present.
Another example: health regulations require community kitchens to use pasteurized eggs, so they can't make homemade mayonnaises. Chefs and researchers wondered whether it would be possible to make an emulsified sauce with an egg yolk pasteurized at 63.2°C for at least 45 minutes. I've shown that it is possible to make such a sauce using precise-temperature cooking, not only with the "perfect egg", but also with the "clay egg" - which opens up interesting possibilities for chefs in the catering trade.
The "clay" egg is a culinary technique I've developed. It involves cooking an egg in its shell at a constant temperature of 63.2°C for 90 minutes. This slow cooking allows the egg proteins to coagulate gently, giving the yolk a texture similar to modeling clay when handled cold.
8. Loss management
Cooking at just the right temperature under vacuum enables you to manage the use of cooked food more precisely. Indeed, as long as they are in their closed cooking bag, shelf life is greatly increased. What's more, depending on the style of catering, individual portions can be prepared, considerably reducing wastage during use.
What are the tips for successful sous-vide cooking at the right temperature?
- Maintain impeccable hygiene, especially if you want to achieve a core temperature close to the minimum required to neutralize bacteria.
- Avoid products touching each other during vacuum packing.
- Check both temperatures: the ambient temperature (the cooking bath) and the core temperature.
- Measure core temperature exactly.
- Take inertia into account when stopping cooking - the greater the difference between the cooking bath and the desired core temperature, the greater the inertia. Cooking in stages helps control inertia.
- For charcuterie, aim for a temperature of 68°C to stabilize color, but avoid going above this to retain the water contained in the meat. A 20% reduction in weight due to water loss has been measured at a temperature of 72°C, with a corresponding loss in sales for products sold by the kilo.
- It's important to work on product preparation and cooking protocols to ensure consistency and reproducibility.
How to cook meat to the right sous-vide temperature?
The cooking bath should be 2°C above the desired final core temperature.
- Vacuum-pack the meat (at a temperature below 6°C) and plunge it into the cooking bath.
- Heat to 83°C for a few minutes to destroy surface bacteria and give the product texture.
- If the meat is to be served colored, it should be colored both before and after sous-vide cooking, to give it the benefits of the Maillard reaction. Be careful not to overheat the meat when coloring.
- If you wish to preserve the meat, leave it in the vacuum bag without opening it, and do not use a cooling cell. Cool in stages, 10 min at room temperature, 10 min in a tap water bath, and 2 hours in an ice water bath, to ensure that the core temperature of the product is below 10°C.
- If you wish to reheat the meat before serving, and there is going to be a further branding operation, it is important to ensure that the core temperature of the meat is not higher than the cooking temperature.
- Meat cooked at the right temperature under vacuum can be kept for over 30 days in cold storage.
- For beef, cook to between 54 and 66°C core temperature, depending on the desired taste qualities. Be careful when cooking at 54°C: you need to be very precise and maintain impeccable hygiene to avoid the development of saprophytic bacteria.
- For a chicken fillet, aim for a core temperature of 62°C at the end of cooking, and use a cooking bath temperature of 66°C.
- Poultry thighs are an exception, as a higher temperature is required to fix the color (avoid pink) of the protein along the bone, which is not really a problem, as it retains its water at higher temperatures than other proteins. We therefore aim for a core temperature of 74°C.
- It's also very difficult to cook game and rabbit at the right temperature under vacuum, because there's too much lactic acid inside the muscles, giving them a cottony texture.
Cooking fish is more delicate than cooking meat, because the shapes and thicknesses of the fillets are not homogeneous, and the flesh is more fragile to work with. But a well-mastered cooking technique yields very interesting results. Especially when using the liquid brine salting system I've developed. This allows you to control the osmotic pressure in the myotomes of the fish before cooking, giving the fillet a beautiful texture and pearly appearance.
How to cook vegetables at just the right temperature sous-vide?
Cooking vegetables to just the right temperature requires a different approach to meat, as the cellular structures are very different. The correct core temperature for vegetables is generally 83°C for an "al dente" texture, and over 85°C for a melt-in-the-mouth texture.
The breakdown of starch, whose hydrolysis is essential for digestion, begins at around 78°C.
The fashion for "al dente" vegetables often leads some chefs to offer vegetables that have been cooked too quickly to boiling or below 78°C, making them particularly difficult to digest. By taking into account the two above-mentioned temperature parameters, cooking at the right temperature under vacuum achieves the right balance between digestibility and texture.
- After washing the vegetables in vinegar and water, season them directly in the cooking bag with 0.5% salt and 1% fat. Fat plays an essential role in fixing the flavors of sous-vide cooking.
- Preferably use grapeseed oil, ideal for its neutral taste.
- Before vacuum-packing vegetables, make sure they are evenly arranged in the bag.
It takes about 10 times longer to cook vegetables at 83°c through than at 100°C (200 minutes instead of 20). - If you're new to sous-vide cooking, limit the use of blended flavors. Prefer simple seasoning, as sous-vide cooking sublimates flavors, and an addition of flavors to the cooking bag could overpower the main taste.
- Once you've gained experience with this cooking method, you can give free rein to your creativity - Expert Chefs and MOFs from EHL have experimented with their creativity by adding a precise amount of orange peel to the endive cooking bag, with delicious results for some, but masking the taste of the endive for others.
Vegetables cooked at just the right temperature under vacuum can be kept for 40 days in cold storage, if the various cooking, cooling and storage parameters are followed precisely.
Note that for green vegetables, cooking at just the right temperature (83°C) will not preserve the green color, which is linked to chlorophyll, which degrades under the influence of heat and time.
Finally, nutrients such as vitamins do not evolve in the same way during cooking. Their degradation varies according to cooking time and temperature. If you want to preserve one vitamin rather than another, you need to choose the right cooking method. Research is currently underway at EHL's Institute of Nutrition R&D to define these phenomena more precisely.
Please note that cooking temperatures and times do not apply to fruiting vegetables, such as eggplants, cucumbers, zucchinis and tomatoes. For the latter, times are highly variable in view of their level of ripeness.
Conclusion
Sous-vide cooking at precise temperatures, the fruit of the application of scientific knowledge to the art of cooking, offers a wide range of possibilities for cooks of all levels. Thanks to the creativity of chefs and the experimentation of nutrition researchers, the properties of food cooked at just the right temperature will continue to open up new sensory experiences.
This article is drawn from discussions at the first conference on precision-temperature cooking, organized by EHL's Institute of Nutrition Research & Development and EHL's Chefs and Culinary Arts Experts, with scientific and technical contributions from Dr. Bruno Goussault, world expert in precision-temperature cooking, and Alain Briquet, Chef and former Hospitality Catering Engineer.
