Under a vacuum : nm The vacuum is a state corresponding to the total absence of any real particle: state of a rarefied gas. Atmosphere corresponding to a state where the pressure is lower than that of the atmosphere ”. But there is a clearer definition which is the following: method of preservation consisting of packaging the product in an airtight packaging from which the air is partially removed. The lack of oxygen prevents the proliferation of microbes.
There are thus 4 types of vacuum, allowed by 4 types of pumps:
- coarse vacuum, obtained from a mechanical pump, used in catering.
- the average vacuum obtained from depressants.
- high vacuum, enabled by turbo-molecular or diffusion pumps.
- ultra-vacuum, obtained by means of ionic or cryostatic pumps.
However, we speak of vacuum, in restoration, only in the case of coarse vacuum. The technique then consists of rarefying a gas or a gas mixture by applying a pressure lower than normal atmospheric pressure (also called depression). Food is cooked for a long time, sometimes well over 24 hours. But unlike a slow cooker, sous-vide cooking uses airtight pouches placed in hot water well below the boiling point (usually around 60 ° C = 140 ° F).
The method was developed by Georges Pralus in the mid-1970s for the Troisgros restaurant (de Pierre et de Michael Troisgros) in Roanne in France. It has been found that food cooked in this way retains its original appearance, does not lose its nutritional properties, and maintains its normal texture. The method is used by a number of major restorers such as Paul Bocuse, Joel Robuchon and many other great chefs.
Non-professional cooks are also beginning to use sous vide cooking.
Clostridium botulinum, a pathogenic bacteria causing fatal food poisoning, can thrive in food in the absence of oxygen, so sous-vide cooking should be done under carefully controlled conditions to avoid botulism poisoning.
To obtain safety and good taste, relatively expensive water bath machines are used: they circulate the heated water with precision, a variation of a few degrees which can affect the finished product.
History of the vacuum: The philosopher Blaise Pascal was the first to work on the vacuum, and in particular on atmospheric pressure. He thus wrote a treatise on the void. With his brother-in-law Périer, Pascal carries out the first experiment. Using two Torricelli tubes, the first installed in the plain, the second placed at the top of the Puy de Dôme, Périer notes that the column of quicksilver (mercury) contained in the two tubes is different. In short, the higher the tube is placed, the more obvious the difference in height of the column. Pascal then redoes the experience, in Paris, at the Saint Jacques de la Boucherie tower. It measures a difference in height of the column of mercury also, of 0,5 cm, between the top and the bottom of the tower, with a height of 50 meters.
Otto de Guérique also highlights the phenomenon of atmospheric pressure, by means of the "experiment known as of the hemispheres of Magdeburg". A metallic sphere is made up of two hemispheres of the same diameter, then they are joined together by means of grease, wax and turpentine. A vacuum is then made in the sphere. Atmospheric pressure brings the two parts together and its action is such that the pulling power of 8 horsepower does not allow the hemispheres to separate again. On the other hand, when a small opening lets air into the sphere, the two parts separate easily.
Evolution of Sous-Vide Equipment: The low-temperature sous-vide cooking method is used by chefs around the world. Enlightened cooking enthusiasts are beginning to learn this technique. The simplest and cheapest equipment is to keep the temperature of the water in a large, heated saucepan as stable as possible using a hotplate and a thermometer. Other enthusiasts buy second-hand laboratory immersion heaters on ebay that must be sterilized and disinfected before use. In early 2008, manufacturers like Auber Instruments and Fresh Meals Solutions offered inexpensive solutions for precise control of the water temperature of a rice cooker coupled with a PID temperature controller and a thermocouple probe.
At the end of 2009, Sous Vide Supreme offered a thermostatically controlled bain-marie (without water circulation pump) and Addélice swid the first immersion heater in the world dedicated to vacuum cooking, both accessible to individuals.
Sous-vide cooking: In general, sous-vide cooking is carried out at low temperature, i.e. between 65 ° and 100 ° C. Food must in fact be pasteurized before being placed under vacuum, which makes it possible to extend the shelf life of the product. However, depending on the type of food, the cooking temperatures differ:
- 100 ° C for vegetables and fruits,
- 90 ° C for fish, seafood or terrines,
- 80 ° C for white meats, poultry and certain sensitive fish,
- 70 ° C finally for red meats, whether roasted or sautéed.
For hygiene reasons, the packaging used must be smooth bags that can only be used with vacuum chamber machines. The heat source must be moist, so that the heat penetrates gradually and evenly inside the food. Cooking times are therefore regular and long. The advantages of sous-vide cooking, or reheating under vacuum, are numerous:
- the product loses little weight;
- vacuum cooking preserves the nutritional and organoleptic qualities of the product;
- cooking is homogeneous;
- it is possible to reheat without destroying the product.