What is the vacuum?
The vacuum packed it is a food preservation technique which is carried out by eliminating, from the inside of a container, the air (up to 99.9%) by suction. Consequently, the food present inside the container finds itself in a negative environmental pressure condition.
Many do not know that the vacuum is also used in the conservation of wine, directly in bottles that are already open; to do this, a hermetic rubber stopper is used to insert into the neck and a manual pump to extract the air. Recently, bottle-shaped wine dowels have also been patented which automatically create a vacuum in the container. This allows the drinks to be preserved. totally your own original bouquet.
Obviously, the vacuum treatment of beverages aims at eliminating as much air as possible, but it is far from the percentages indicated for food vacuum packing. This is mainly due to the rigidity of the container (glass) which does not allow the air contained in it to be completely extracted.
Vacuum packed frozen food
Why also vacuum a frozen food?
With regard to this "last technique, certainly little used compared to the others, many readers will wonder what its usefulness could be. The answer is quite simple; it is not a question of shelf-life (life of the product or shelf life), but rather to maintain the organoleptic and taste characteristics.
The "vacuumed" foods, especially those cooked and then frozen (preferably chilled), totally preserve the original flavor and aroma. With this technique, the classic drawbacks of storage at negative temperatures are avoided, which are:
- Deterioration ("cooking" with the cold) of the food surface and discolouration as well as of the consistency
- Acquisition of a smell and a taste that can be better identified as "taste / aroma of the fridge or freezer".
It follows that vacuum-packed frozen foods can prolong their integrity longer than normal and that they make use of greater organoleptic and gustatory characteristics even near the shelf life (for a product processed at home, no more than 1-3 months, depending on the temperature).
Means and tools
To induce vacuum in food, two fundamental components are required: the machine and the containers.
The vacuum machine, also called vacuum, is an instrument that extracts the air from the bag containing the food and seals it by heat sealing in two strips, respectively placed at the top of the container. There are two versions: bell and bar; the bell is certainly the most effective.
The vacuum bags are plastic (or polyethylene) or aluminum containing bags, suitable for food. They can be smooth and single-portion, embossed and in rolls, for cooking, or even anti-UV rays (usually used for meat).
The vacuum packing process is quite simple. The food is put back in the bag, the opening of the same is placed in the machine and then, once started, the air is extracted and the heat sealed. ATTENTION!
The most common mistake in vacuum packing is to dirty the top of the bag; in doing so, the heat sealing will not be completely effective and will suck (more or less quickly) the external air through the defective closure.
Effectiveness
The effectiveness of the vacuum method for preservation is mainly linked to the elimination of oxygen. This gas, which is present in the air only for 21%, is a powerful oxidizing agent and causes the browning of foods. part of the microorganisms responsible for food degeneration is type aerobic, that is, it lives and multiplies thanks to the presence of oxygen (a bit like the human being!). In practice, thanks to the vacuum, food preservation is prolonged by acting on two distinct fronts: bacterial inactivation and the reduction of non-enzymatic oxidation of food.
Contraindications
Certainly, reading what has been written so far, it would seem that vacuum packing is the definitive solution to all food preservation problems. Obviously this is not the case!
First of all (fortunately, today less than in the 90s) a good professional bell vacuum has a very low cost. You can find first choice instruments ranging from 1500 € up to almost 13000 €; it's not cheap! As if that weren't enough, even vacuum bags (plastic or aluminum) are certainly not among the "cheapest" items; we specify that they are "disposable" containers, at least in theory! The multiple use of these bags causes a considerable increase in the risk of food contamination, which totally nullifies the use of vacuum packaging for conservation.
There is also another rather important vacuum defect. In the heat-sealing component of the machine (especially when storing liquid food or using used bags) there is an accumulation of food residues as a critical point of the so-called cross-contamination. Once again, the risk is that of totally nullifying the use of vacuum packing for conservation.
Another very important clarification must then be made; the vacuum does not destroy the mixed bacterial load nor does it completely inhibit it. This happens because many microorganisms are able to live or survive even in promiscuous conditions; it is the case of bacteria facultative aerobes / anaerobes. These microorganisms, which tolerate the environment with and without oxygen, while boasting greater proliferation in one or another circumstance, are always active. obligate anaerobes, that is, those that grow only in the absence of oxygen; it is therefore deductible that the vacuum can only facilitate its life cycle. It's not all; even taking into account only the bacteria obligate aerobes, which should perish in the absence of oxygen, some of these still manage to survive. This adaptability is due to its potential sporogenous; they are able to protect themselves from within spores which act as real armor. The microorganisms therefore fall into "hibernation" until the optimal conditions for hatching / germinating are reached.
By "cutting off the bull's head", to prevent one or more of the aforementioned circumstances from manifesting itself, vacuum cooking was invented. By applying heat treatment to already vacuumed foodstuffs it is possible to induce the pasteurization of the food and, at times, ALMOST achieve sterilization. Obviously, not all microorganisms are the same. NON-spore-forming ones that grow at low or medium temperatures are the first to die; at the same time, others resist higher temperatures and, finally, the spores do not perish even at boiling temperature.
Vacuum cooking
As anticipated, the last frontier of the vacuum is that which allows the application of cooking. This, originally applied only in a steam or mixed oven, for medium and large sized foods (mainly meat), is now widely used also by boiling or in a pressure cooker and also affects vegetable foods.
The process of vacuum cooking in the oven is simple: after creating the vacuum (sometimes with the integration of modified atmosphere), cooking is applied (more or less prolonged depending on the product) at programmed temperatures of 65-98 ° C.
As for the vacuum cooking of small foods, perhaps of vegetable origin, it is instead sufficient to immerse the vacuum bag in boiling water up to the desired cooking level. The BIG advantage of short vacuum cooking for vegetables is due to the fact that these, due to the degradation of cellular enzymes, DO NOT oxidize and totally maintain the original color, taste, aroma and consistency.
Another plus
We conclude the article by mentioning a big advantage of sous-vide cooking. Due to a matter of environmental pressure inside the vacuum-sealed bag, which we remember to be NEGATIVE (ie <1 bar atmospheric at sea level), the boiling temperature drops considerably. This means that if I immerse a vacuum packed food in cold water in a pan and then if I put this last on the fire, the food will start to cook faster and at lower temperatures. Obviously, due to gas expansion, the atmosphere inside the envelope will also slowly become positive; however, if the heat sealing is successful, this (once the original temperature is restored) will again become negative and vacuum.
The advantages of this system are different; in addition to the shelf life, which we have already talked about, the following are observed:
- A greater freshness of the food at the time of use, therefore an optimal maintenance of color, aroma and taste
- An exceptional preservation of food liquids.
This last point therefore allows to gain greater food yield and lower the costs of raw materials.
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