Among the technologies applicable to restoration, vacuum technology made its appearance relatively recently as a cooking method and not just conservation.
Since vacuum technology appeared, it has had a fairly rapid application in the mechanical, chemical, and metallurgical industries. The agri-food industry was interested in its advantages in preserving manufactured food.
It was some time later that the idea of using this technique as a cooking procedure and not just preservation appeared. This is how the kitchen vacuum being able to distinguish now between kitchen vacuum as such, which would be vacuum packaging of previously cooked products and vacuum cooking, which is the technique of cooking food once packaged. A more detailed explanation of these differences can be found in the chapter dedicated to fundamental concepts.
This work is structured according to the order of information that a reader who is just beginning to read this topic would follow. We start with a brief explanation of the basic concepts that will be handled throughout our presentation and that the reader must take into account for a correct understanding of the terms that we will use.
The second chapter is devoted to exposing the history of the use of vacuum from the first experiences with it to the latest advances in vacuum cooking. The references that we will make about its use in the non-food industrial field will be very quick, and we will focus instead on the path followed to reach the use of this technique in catering.
The third chapter deals with the subject of the vacuum technique, considering general aspects of the use of the technique, such as the types of vacuum that can be achieved, the different types of vacuum machines available to date, the characteristics of the bags vacuum and the gases used to make the packaging in a modified atmosphere, etc.
Next, we focus on the subject of the vacuum technique from the two most common uses within the restoration, which are conservation and vacuum cooking. We address the issue of conservation by explaining the different options we have for packaging products according to their own characteristics and the advantages of keeping them stored under vacuum and even freezing them.
The subject of vacuum cooking deals with issues such as types of vacuum cooking, cooking times, some specific techniques for specific products, the advantages of such cooking, etc.
Finally we present some culinary preparations in which vacuum cooking intervenes on different products.
The Larousse encyclopedia defines the term "vacuum" as the environment corresponding to a state in which the pressure is lower than that of the atmosphere. Applying this definition to the kitchen, is a system for preserving raw, semi-prepared or cooked food, which, based on the absence of oxygen in the air, prevents the development of the aerobic bacteria that cause food rot.
This process has long been only a method of preservation, but not a technique of kitchen proper.
I.2. Vacuum cooking
One of the fundamental problems in cooking is the loss of flavors in the products due to oxidation during cooking in the open air. The ideal therefore would be to cook without the presence of oxygen. Vacuum cooking implies cooking at a lower temperature than usual (between 55ºC and 98ºC) for a longer period of time and without the presence of oxygen in contact with the products. This is achieved by packaging the products without air in airtight and heat resistant containers. For technical reasons, a small amount of liquid is added to the container, be it water or the product's own juice to obtain a humid environment.
I.3. Vacuum Cooking and Vacuum Cooking
There are differences between what is vacuum cooking and vacuum cooking. The main difference is that in vacuum cooking food is cooked in the traditional way and vacuum packed after rapid cooling. In vacuum cooking the food is vacuum packed in raw and cooked in this packaging.
I.4. Extraction Packaging
It consists of eliminating the air contained in the bag or tray where the food is located, with which the container takes the shape of the product. This method is used to package foods that are sufficiently rigid as meat or deformable as sauce.
I.5. Displacement Packaging
It consists of replacing the air contained in the bag or tray with a mixture of inert gases, creating a controlled atmosphere that prevents the proliferation of microorganisms. It is used for fragile products, those that would be crushed if the air were simply removed from the container.
I.6. Concentration cooking
It consists of cooking the food at low temperature and for a period of time longer than that used in traditional cooking. The action of heat is exerted on the entire surface of the food at the same time. It penetrates towards the interior in a uniform way, maintaining the texture and concentrating its aromas.
II. History of Vacuum and its Application in Kitchen
Vacuum technology is not new. Blaise Pascal (1623-1662) worked from a young age on problems related to emptiness. He is owed the laws on atmospheric pressure as well as a vacuum treaty.
In the seventeenth century the weight of air and the phenomenon of the ascent of liquids by aspiration became known. However, the relationship between the two was ignored and the suction phenomena were explained by a supposed "horror" that nature has for the vacuum. Galileo, Torricelli and Pascal then sought a scientific explanation for this phenomenon. Pascal finally found and explained the relationship between atmospheric pressure and height above sea level. In this way the existence of the void was also verified.
The industrial use of vacuum began with the preservation of consumer products such as coffee beans or ground coffee to preserve its aroma, milk, fruit juices, canned vegetables and fruits. Later it was used for the preservation of dishes already prepared.
Studies in gastronomy began in 1974 with Georges Pralus in his laboratory in Briennon, France. Faced with the problems of losing weight of foie gras during cooking (between 40 and 50% of its weight), Pralus tried techniques to reduce this loss, finding that cooking of foie gras in vacuum achieved only 5% loss of weight and quality end of the product was optimal.
In 1988 Yves Sinclair and Felipe Abadía gave the first vacuum cooking talks at the ALIMENTARIA fair in Barcelona. In the 1992 edition of this fair, the Vac Club appeared, bringing together the first professionals in the field.
III. The Void Technique
III.1. Different Applications of the Technique
a) Raw preservation
Once the genus is cleaned, we proceed to its raw packaging for storage in the cold room. We label with the packaging and expiration date. Then it is deposited in the cold room until it is used.
- b) Traditional cooking and vacuum packaging
When we have portioned the genre, we proceed to cook it in the traditional way. Once cooked we have two options:
- Rapid cooling and packaging of the product. The fabric must be quickly cooled to 10ºC in the center and 2ºC outside. Once cooled, it is packaged and labeled.
- Pack hot and then cool. Hot packaging is carried out once the goods have been cooked. Then we package and cool to 10ºC in the center of the product as quickly as possible.
The advantage of both options is to keep the traditional kitchen applying a modern and practical conservation system.
- c) Vacuum cooking proper
It consists of cooking the fabric after it has been vacuum packed. For meat cases, it is preferable to mark them on the plate beforehand so that they have a golden color. As in the previous case, a quick cooling must be applied to the product once cooked.
III.2. Different Types of Vacuum
The different nature of the products to be vacuum packed determines the vacuum technique to be used:
- Normal vacuum
Made on raw, marinated or cured products. It is simply a matter of extracting the air contained in the product and closing the bag by heat sealing. It can be total or partial, that is, close to 100% vacuum or with residual air inside the bag.
- Continuous vacuum
Extending the time in which the action of the vacuum is carried out to achieve a higher percentage of vacuum (also known as "vacuum improvement"). Large pieces are used that must then be cooked in the bag, such as York ham.
- Vacuum of a hot product
When packaging a hot product, a partial vacuum will be applied, proportional to its temperature, since in hot products the amount of oxygen is greater and more difficult to extract.
In general, the less water the product contains and the colder it is, the greater the vacuum obtained in the container. For example, with some spinach packaged at 70ºC only 69,2% of vacuum will be obtained.
In principle, it is not advisable to pack hot products because there is no real vacuum, apart from the risk of damaging the vacuum pump. For more details see section a) of point III.3.
- Vacuum compensated
It is used for the packaging of fragile products. Once the vacuum has been created, an inert gas or gas mixture is injected into the bag, thus obtaining a gas cushion that absorbs the external pressure. It is also used for raw red meats, when we want them to maintain their red color thanks to oxygen or in fresh vegetables, so that they can continue “breathing”.
III.3. Vacuum application precautions
a) Heat, enemy of emptiness
There is a close relationship between atmospheric pressure and the temperature at which water boils. Under normal conditions, corresponding to a pressure of 1 atmosphere, pure water boils at 100ºC. At a pressure less than one atmosphere, the water will also boil at a lower temperature. Thus, at a pressure of 0,1 atmosphere, water boils at 60ºC, and at 0,01 atmosphere, it boils at only 10ºC.
Therefore, in a vacuum machine, when the pump begins to produce the vacuum inside the hood, the atmospheric pressure decreases inside it and the water contained in the food begins to boil, even when it is at room temperature inside a kitchen.
When we apply a vacuum to a hot product, the pump is charged with air with water vapor, thus losing efficiency. To vacuum pack hot products, we must do a partial vacuum, this to prevent the atmospheric pressure from dropping too low and reduce the risk of boiling. The steam released by the hot food will condense as the food cools inside the bag, leaving it in a liquid state again. It is for these reasons that it is always best to cool food in a cooling cell before packaging.
- b) Food, before being vacuum packed, must be physiologically dead.
This is mainly the case for shellfish. For example, it is a serious mistake to vacuum-pack raw mussels in their shells and not cook them right away. The living animal, deprived of oxygen, suffocates, dies and quickly decays.
On the other hand, raw fruits and vegetables are always "alive", whether they are peeled, washed or chopped, so they can ferment and rot. For this reason, they must always be bleached before being packaged, in order to cut their enzymatic activity, or they can also be packed raw but cooked immediately under vacuum.
- c) Food must not have sharp or sharp parts
Vacuum bags do not support perforation, so caution should be exercised when packaging foods that have sharp points or edges, such as crustacean legs and claws, fish fins, etc.
III.4. Vacuum Machines
The vacuum machine is a complex apparatus, consisting of a series of sections specialized in extracting air from the bag and the product, injecting an inert gas if necessary, and sealing the bag. A pump is responsible for vacuuming up to 99%. It also has a stop system in the event that the suction force is excessive for a given product.
The injection of the inert gas is controlled by a program that controls the intensity and duration of the gas flow. The bag sealing system consists of two resistors that melt part of the plastic in the bag while a rapid cooling system allows the sealing to be completed before the hood is opened. Once the sealing process is finished, a valve allows air to enter the hood gradually.
Vacuum machines have the following basic components:
- vacuum gauge
Through it, the degree of vacuum inside the chamber is controlled. Some machines are equipped with the so-called Sensor Control. This system makes the vacuum pump work to the degree of vacuum preset by the user, without the user having to calculate the emptying time according to the type of part that is inserted into the chamber.
- Gas injection system
This system introduces the gas into the container once the vacuum has been made and just before sealing.
It is not something essential for all machines, since its need depends on the type and characteristics of the product to be packaged.
- Sealing system
The machine must be equipped with a system that allows the bags into which the food is introduced to be welded, so that, once it is out of the chamber, the oxygen in the air does not come into contact with the packaged material. Welding can be single or double.
- Progressive Atmosphere Valve
Controls the speed of the air entering the chamber once the vacuum has been created. It is also not an essential element in the emptying process, although it is highly recommended for fragile or sharp products, since by allowing the entry of air into the chamber to be delayed, it facilitates the bag to adapt without abruptness to the shapes of the packaged material.
III.4.1. Minimum maintenance of a vacuum machine
- Empty it regularly every 300 hours of use.
- Control that the hermetic seal of the hood lid is in perfect condition, that it is not broken, to prevent the entry of outside air.
- Make sure that the Teflon coating on the resistor solder is not burned. If this is the case, replace it quickly and pass an emery cloth through the resistors to extract the calamine. Put the Teflon back on.
- Thoroughly clean the inside of the hood and lid using warm water and antiseptic detergent, as well as the interior trays. Rinse well.
- Avoid pouring liquids into the pump port, as it reduces the efficiency and life of the pump.
- Never wash it under running water.
III.5. The bags
Bags are also of central importance in the vacuum process. For each case, you have to choose the type of bag appropriate to the requirements. The bags must have the necessary strength so that they do not break during handling or be damaged when heated or cooled. As they must also be able to be heat sealed, the bags are made of several layers of plastics that meet the desired characteristics, many of them contradictory to each other.
Thus, the outer layer should be resistant to heat and tampering. The intermediate layer will be of low gas permeability. The inner layer, on the other hand, will have a low melting temperature to facilitate sealing.
There is a type of shrink bag that is resistant to high temperatures for cooking and preserving food that needs to be well secured and also prevent exudation. Submerging the bag in water at 90ºC, it is possible to retract it and mold it to the product.
There are several types of bags:
- Conservation bags
These bags have a thickness of 100 to 150 microns, depending on whether the product contains bones or sharp points.
- Cooking bags
They are resistant to temperature within the range of + 120ºC to 40ºC below zero. However, these bags do not resist the heat of a conventional oven, or convection or infrared rays. If they resist microwaves as long as some perforation is made, with which, microwave ovens can only be used to regenerate.
There are also different types of plastics incorporated into the vacuum technique:
- Polypropylene (-20ºC to 120ºC)
Suitable for sealing, vacuum, gas vacuum, pasteurization and freezing.
- High density polyethylene (-40ºC to 110ºC)
Suitable for sealing, vacuum, gas vacuum, pasteurization and freezing.
Very permeable, used for dairy.
Disused by European economic and ecological policy
Union of two plastics. Normally one makes a barrier to gases and the other to water vapor.
- Apet (-40ºC to 65ºC)
Suitable for sealing, vacuum, gas vacuum, freezing and products to be kept refrigerated.
- Cpet (-40ºC to 220ºC)
Suitable for sealing, vacuum, gas vacuum, pasteurization, freezing and direct cooking in the same container.
- PS Expended + PE
Suitable for conservation in a protected atmosphere, replacing the current PS. Suitable for sale in large stores.
III.6. The gases
Under normal conditions nitrogen is a colorless, odorless and tasteless gas. Liquefied nitrogen is the cryogenic fluid par excellence for processes, cooling and deep-freezing. Its qualities are chemical inertness, that is, it does not attack or react with other bodies; its cooling capacity is also non-toxic and low-priced.
This liquefied gas is insoluble in water and gases. When injected into the bag, it produces the displacement of oxygen, thus preventing oxidation and inhibiting the growth of aerobic microorganisms, but not that of anaerobes. It also prevents deformation of the container.
b) Carbon Dioxide
Also called carbon dioxide, it is a colorless, odorless, and acid-tasting gas. It is not toxic or flammable. It displaces oxygen from the air with the same effect as nitrogen. Because it is an inert and antioxidant gas, it can be used to preserve food products whose contact with oxygen is harmful (meat and certain types of wine).
It is soluble in water and gases, it has bacteriostatic and fungicidal action in values higher than 10% and at low temperature, which allows to stop the growth of all microorganisms, be they aerobic or anaerobic. It also dissolves in water, leading to a slight reduction in the pH of the medium.
It's a colorless, odorless, and tasteless gas. It is a chemically reactive gas and combines with other elements. It is used almost exclusively to maintain the red color of the meat and help maintain the metabolism of vegetables, but its effect is negative on the vast majority of foods, since it produces their oxidation and also the rancidity of fats and oils. It is used in very low concentrations.
III.7. Basic Equipment
- Essential machinery
- Vacuum making machine
- Materials for cooking
- Convection oven
- Mixed oven (convection and steam)
- Water bath with thermostat
- Cooling materials
- Cooling cell
- Complementary materials
- Waterproof and heat resistant containers (bags or trays)
- Conservation materials
- Positive cold chamber (between 0ºC and 3ºC)
- Negative cold chamber (between 0ºC and –18ºC)
- Materials for regeneration
- Mixed oven
- Convection oven
- Water bath with thermostat
- Microwave oven
IV. Vacuum Conservation
IV.1. Fields of application of the procedure
- Cured products (hams, sausages, marinades)
These products, which in themselves are long-lasting, if we vacuum-pack them, extend their expiration dates even further and obtain additional advantages. For example, there is no weight loss or drying out. Furthermore, there is no risk of acquiring strange odors because each product is in its respective container isolated from the rest. We can even save products already filleted like Serrano ham.
- Fresh or semi-prepared products
In the case of meats, vegetables, pasta, fish, salads, marinades, etc., we were able to isolate them from the outside and therefore from any contaminating agent that may cause poisoning. Likewise, we extend its shelf life in the chamber and avoid drying out and acquiring strange odors.
- Traditionally cooked products
It consists of the semi-preparation of a wide range of cooked products, which will be vacuum-packed to improve their preservation.
Precooked products such as cannelloni, lasagna, etc., can be packaged at any time during their preparation, even when golden.
- Cooked and packaged products
Almost any product cooked in the traditional way can be packed, respecting rigorous temperature and hygiene controls. With vacuum packaging we achieve better preservation and save effort in the manufacturing process, since we can produce them in advance and keep them preserved until use.
IV.2. Food packaging in protective atmosphere (EAP)
This technique is used interchangeably for cooked and raw products. In the restoration it is used for products that due to their consistency could be crushed by the action of atmospheric pressure after vacuuming, for example salads, pastries, lasagna, etc.
The technique consists of practicing the total vacuum and injecting a gas or gas mixture into the bag and sealing it. The action of these gases has the objective of inhibiting the mechanisms of food deterioration due to the growth of microorganisms, oxidation and enzymatic action. The gases used are Nitrogen, Oxygen and carbon dioxide or mixtures of them.
To analyze the use of gases in product packaging, we must divide the products into three groups:
- Dry goods
For the packaging of products with a minimum water content, whose main problem is oxidation, we will vacuum and complete with a Nitrogen atmosphere. This would be the process for coffee, chips, nuts, etc.
- Products with medium water content
This type of products can present oxidation problems and the presence of bacteria and molds. In this case, a mixture composed of Nitrogen and carbon dioxide must be used, since the latter controlá bacterial growth. It should be stored at temperatures between 0 and 2ºC, since the bacteriostatic action of carbon dioxide is more active at low temperatures and decreases progressively as the temperature increases.
- Products with high water content
The main problem with these products is bacterial growth, so we opted for an oxygen-free atmosphere. But there is also the problem that meats turn brown due to the lack of oxygen. It is not so important to keep the red color of the meats compared to keeping them fresh and saving time in conservation and maturation. When you open the bag, the meat will slowly regain its red color.
If, on the contrary, we wanted to maintain the red color of the meats, the gas mixture would be 60% oxygen (for the color), 20% carbon dioxide (for bacteriostatic action) and 20% nitrogen as a neutral supplement.
The precooked ones are packed according to their fragility. Those that need a protective atmosphere are packaged with a mixture of gases, those that contain sauces can be packaged under total vacuum since it dampens the action of atmospheric pressure on the product.
IV.3. Freezing Vacuum Packed Products
Vacuum packed products can be frozen, however, it is advisable to pack them within a controlled atmosphere to avoid the product suffering negative vacuum pressure. To defrost them, simply follow the normal defrosting process, always preferring a slow defrost to a violent one.
V Vacuum Cooking
V.1. What is Vacuum Cooking
To cook in a vacuum is to place a food in a watertight and heat-resistant container, extract the air inside it, seal it tightly and subject it to the action of heat at a constant temperature and for the necessary time.
Cooking is carried out at temperatures below 100ºC and will necessarily be followed by a rapid drop in temperature. It is a concentration cooking, since the food is cooked at a low temperature inside the container and for a longer time than normal. The action of heat must be uniform to achieve perfect cooking.
Vacuum cooking requires a humid environment, whether the product itself contains plenty of water or a little water has been added at the time of packaging. For example, dried legumes will have to be soaked for hours before packaging, whereas potatoes and carrots will only need one tablespoon of water per kilo.
The temperature must be identical during cooking without varying more than 1ºC at all points of the cooking chamber. This is achieved with a water bath with a thermostat or a low pressure steamer.
A simple way to explain vacuum cooking is to say that instead of cooking, as is traditional, food at 130ºC heat for a relatively short period, here they are cooked between 65ºC and 99ºC in longer times depending on the nature of the genre and His weight. It is therefore a long and low temperature cooking. In a conventional oven, a piece of meat is cooked at 200ºC, which causes the exterior to toast, however, the temperature at the heart of the piece rarely exceeds 50ºC. Therefore, only a temperature equal to or slightly higher than 65ºC is necessary to cook a food, avoiding drying out and hardening of the muscle fiber as well as overcooking.
The rapid temperature drop must be carried out immediately after cooking and must be able to ensure that the temperature in the center of the product falls below 5ºC and in less than 90 minutes, for which the cooling cell is used.
To regenerate the product, that is, to bring it back to serving temperature, we can use a steamer, convection oven or microwave oven. In the latter case, it is necessary to previously make a hole in the bag to prevent it from bursting. We must achieve a temperature in the center of the piece of about 60ºC to 70ºC, which is the coagulation temperature of proteins, albumins and starches; otherwise we will be prolonging the first cooking and we will destroy the qualities of the food and the results of the process. Temperature recovery should not take more than one hour. And that's it. It only remains to cut the bag and give it a culinary touch when appropriate, such as the addition of certain sauces that must be tied according to the old way.
Once the product has been reheated, it is totally forbidden to package it again for a new conservation.
V.2. Basic Principles of Vacuum Cooking
- Rigorously apply hygiene in all its aspects during the phases to be followed for raw packaging, cooking or vacuum cooking. This implies the perfect cleaning of products, containers and the place where the process takes place. Never use a bag again.
- Use raw materials of an indisputable quality and degree of freshness.
- Achieve a 99% perfect vacuum
- Cook the product quickly rising to the desired temperature to exceed the danger zone (10ºC to 65ºC) as soon as possible, which is the range in which the bacteria develop more quickly.
- Quickly cool any cooked product to 10ºC. This operation should be done in less than 90 minutes.
- Control permanently the health of the staff, their hygiene and that of their clothing.
- Label the bags with the date of manufacture and expiration.
- Store packaged products in refrigerators at temperatures between 0ºC and 2ºC, and respect that temperature until heating and serving.
- When recovering the temperature, it is necessary to exceed 65ºC in the heart of the product in less than an hour.
- The authorized refrigerator storage time for cooked and vacuum-packed products is 6 to 21 days maximum. In freezing, the time may be longer depending on the product.
V.3. Types of Vacuum Cooking
Different cooking temperatures are used today depending on the chosen vacuum cooking procedure. So we can distinguish:
- a) Vacuum cooking at high temperature
Cooking between 100ºC and 135ºC. Especially used in large industries to ensure a longer shelf life of the product. Also for cooking certain vegetables and legumes.
- b) Vacuum Cooking Properly Said
High temperature of the cooking medium (water vapor), between 70ºC and 100ºC. Low temperature at the heart of the product (60ºC - 70ºC)
- c) Low Temperature Vacuum Cooking
Cooking temperature between 65 ºC and 70ºC. These temperatures are the same for the cooking medium as in the center of the product.
V.4. Cooking Temperatures and Times Chart
|PRODUCT||VACUUM INTENSITY||TEMPERATURE||COOKING TIME|
|Fruits and vegetables||4-5 or 40 seconds||100 ° C||Same as traditional|
|Fish and seafood||3-4 or 35 seconds||85ºC||Same as traditional|
|White meats||5-6 or 45 seconds||80ºC||Additional 50%|
|Red meats||7-8 or 50 seconds||75ºC||Twice the time|
|York ham||Three continuous minutes||65ºC - 70ºC||14-16 horas|
|Liver||1 min continuous or 10 on the knob||70ºC if it is first, 65ºC if it is second||9 min for every 100g.|
- Asparagus must be blanched first because they need oxygen to fix the chlorophyll. Then they are packaged and cooked for 4 min at 99ºC. In traditional cooking, the asparagus are cooked in an upright position because in their lower part they have more fiber than in the heads; This way, even cooking is obtained. In vacuum cooking, this difficulty is overcome because the pressure they receive makes the distribution of extracellular water uniform over the entire surface of the asparagus. Thus the fiber will be well irrigated and cooking will not require a different time for the heads and stems. The flavor obtained by vacuum asparagus is unsurpassed.
- To cook carrots, turn them and pack them only with 2 tablespoons of water. Potatoes the same. Without salt. Cook in a steamer at 99ºC for 20 min. Then cool.
- Mushrooms are packaged washed only. They are cooked for 3 min at 99ºC. Vacuum cooking preserves them from oxidation, for which they are so sensitive.
- Artichokes are packed without adding anything. They are cooked at 99ºC for 20 min.
- Endives are packed without adding anything.
- To confit potatoes, package them turned with 1 tablespoon of oil. Cook at 99ºC for 20 min.
- If raw vegetables are packaged to keep them raw, make a partial vacuum at 80%
- The lettuce once washed is packaged at 70% vacuum
- The zucchini is cooked at 99ºC for 4 min.
- The rabbit is candied with 1 dl. of oil and aromas for 20 min. at 80ºC
V.5. The Marinades
A complementary application to vacuum cooking is vacuum marinade. The pressure obtained inside a vacuum bag and the absence of air make the acquisition of flavors and aromas in a marinade amplify and accelerate. Therefore, the marinade that we will obtain will be more defined and in a shorter time. The marinade will always be carried out at a temperature of 3ºC.
V.6. Advantages of Vacuum in Today's Kitchen
- Preservation of organoleptic qualities
Vacuum cooking preserves and enhances the natural flavor of food, since when cooking in an airtight and air-free room there are losses of volatile aromas. Also, there is no loss of flavors when reheated. The products to be used must be of the best quality, which will be optimally preserved by vacuum.
Vacuum cooking results are particularly good on fresh fish, foie gras and legumes.
Let's not forget that vacuum cooking is a more technical way of cooking in papillotte, in which all the flavors are imprisoned inside the bag, that is, they are not lost with evaporation. Perhaps we could assure that this is one of the main qualities of this technique. It favors the concentration of aromas and accentuates the natural appearance of the products.
Another advantage is that when cooking at low temperature and in a humid environment, the heat is evenly distributed throughout the product, obtaining a very regular cooking quality.
- Great dietary and nutritional value
The heat always destroys some small part of the nutrients and if it is very intense heat, as in roasts, the losses are greater. Some of the water-soluble nutrients, particularly vitamin C from fruits and vegetables and vitamin B, from meats, remain in the water used for cooking. These vitamins are used if the juices resulting from the same cooking are consumed.
According to the cooking method and the medium used (water, fat, etc.), physical changes will occur in the structure of the food, which is good to keep in mind. In any of the traditional cooking methods, the change in volume of the cooked products is perceived with the naked eye. The loss of water is accompanied by the disappearance of properties and elements of the composition of food.
In a vacuum, cooking without oxidation of the product avoids alteration of taste and its molecular conception, due to the absence of changes in vitamins, fats and enzymes.
Dietetically it is also an improvement compared to traditional cuisine, since when cooked under vacuum the food does not lose moisture and is cooked at low temperatures, with which we manage to keep almost all of the vitamins, especially water-soluble ones. Food remains juicy and does not require long sauces, being able to dispense with fats almost entirely.
It is an important technique not only for people in the world of catering, but it is also of great interest to dietitians and nutritionists since, in addition to preserving the properties of food, it makes it more digestive by eliminating the fermentation phenomenon produced by the air. It is even being carried out in hospital centers for the treatment of different diseases.
Regarding the physical modifications produced within food, some aspects such as the following should be highlighted:
- Proteins, when they reach 50-60 degrees, change color and tend to coagulate.
- In some foods, burning or browning too much forms toxic substances.
- Starches cooked in liquids tend to inflate by the absorption of the liquid and change their structure to form a high-viscosity colloid making the food unattractive, as in the case of rice and pasta that become sticky.
- Fats at very high temperatures break down forming toxic substances such as acroleins.
- Vitamins are denatured in prolonged cooking. They withstand high temperatures for a short time better than low temperatures for a long period of time.
- The mineral salts do not change but they can pass to the cooking medium, therefore losing the food part of its nutritional value that passes to the liquid.
- Perfect freshness and hygiene
The elimination by the vacuum of the aerobic microbes, makes that during cooking a type of pasteurization is achieved that lengthens the shelf life of food.
The bags also protect the transmission of flavors or odors foreign to the product inside the refrigerator, as well as drying.
Avoid further contamination, both in stock and in transport, since the product is heat-sealed. It also prevents possible liquid spills.
The problem of leftovers is eliminated, since the trays, until they open (loss of vacuum) can be used until the expiration date (up to 21 days depending on the product), keeping them at 3ºC. There is also the possibility of freezing before the expiration date, thus extending the life of the product (from 3 to 6 months).
The vacuum preservation system helps us keep the aromas of freshness both in cooking and in the natural. The preservation of all the aromas will be possible as long as we buy the products as fresh as possible; We will never pretend to enhance a mediocre product as vacuum is not a panacea of good quality. Thus, one of the golden rules of vacuum is to buy freshly harvested products, with which we will obtain a maximum quality for our restoration, which, in fact, is what interests us. And at harvest times, the products will be more affordable, achieving better yields.
- Work organization
Distributing work during periods of lesser influx of public allows to better organize work, make staff more profitable, distribute schedules in a more rational way avoiding overtime and allowing a better distribution of free hours. Thus, a mise en place is achieved for the busiest moments. Pre-preparation of banquets and buffets can be advanced. In this way, we will be able to expand the number of dishes on the menu and a faster service of constant quality will be obtained.
With this system we ensure that the service is never lacking and we reduce the consequences of a strike, vacation, casualties, etc.
It also enables the creation of a great variation of menus with the range of dishes on offer or even à la carte dishes.
- Economic Advantages
You can increase the profitability of products by making advance purchases in times when each product is of better quality. This way we will get better prices and better quality in the products we buy. The portioning of the products is improved by doing it without haste, the portions are more even and the leftovers can also be packed for future uses. Simultaneous cooking of several products is possible.
The products have lower losses by reducing the evaporation of liquids. We also increased the storage capacity of the cameras by having everything bagged, since products can be stored together that without vacuum packaging would be impossible. When packaging rationed products, stock control is real and therefore the purchase forecast is made with greater accuracy.
There is a significant reduction in general expenses (electricity, water and gas). Cleaning costs are also reduced in the sense that the food at the time of being served is heated directly in its bag without the need for other utensils. With this, time, detergents, water and labor are saved.
If we make a comparative table of the cost of a kilo of foie gras, beef tenderloin, salmon, tuna and chicken, we will notice the savings achieved by using the vacuum cooking technique, which constitutes the amortization of the cost of the necessary machinery to apply this technique.
|TRADITIONAL COOKING||VACUUM COOKING|
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SAW. Application of the Technique
VI.1. General applications
In this section we present some examples of application of the vacuum technique according to food groups.
- a) Sauces
Once finished making the funds, we proceed to make the sauces according to the usual way. It is recommended to prepare them in a traditional way. Once the reduction and wetting of each sauce has been carried out, it is rectified with salt and, if necessary, they foam and strain. Then they are vacuum packed and pasteurized or sterilized. The bagging must be done as in the bottoms, in half or one liter bags and followed by rapid cooling, for subsequent storage in a cold store without losing the cold chain.
The vacuum percentages range between 90 and 100%, they can be packaged in a modified atmosphere and the shelf life is similar to that of the kitchen stock.
- b) Hors d'oeuvres and Deli
To preserve canapés, the percentage of vacuum ranges between 90% and 99%, and we will normally use gas in their packaging (from 20 to 30%).
For hors d'oeuvres with vinegar, vacuum packaging further prolongs the preservation of the vinegar.
- c) Delicatessen
The delicatessen products extend their shelf life without being 100% vacuum-packed. For products such as pates and terrines, the expiration period will be determined by the sterilization pasteurization process to which it is subjected.
- d) Soups and Creams
Soups and creams are made in the traditional way and are packed with an 80 to 100% vacuum. In the case of crushing or straining, it is necessary to re-boil (lift) them before packaging.
- e) Meats
Vacuum packaging facilitates the rest to which the meat must be subjected so that the fibers soften. If we take this rest with the packaged product, we will avoid the dryness and the taste and odor of the chamber that the meats acquire. The percentage of vacuum applied is 100%.
Vacuum packaging is also suitable for fish and shellfish.
- f) Pastry
Raw creams, sauces and doughs can be vacuum packed for better preservation with or without fermentation. In the case of the masses, they must be frozen before packaging and kept like this.
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Monograph Posted by Carlos Del Pozo in Monografias.com