Generality
Oysters are fishery products of animal origin, belonging to the Phylum of Molluscs, the Class of Bivalves and the Ostreidae family. There are therefore different types of oysters, belonging to different genera and species; of all, the most used and known ones undoubtedly belong to the Genus Ostrea (common oyster - Ostrea edulis ) and Crassostrea (Pacific oyster or Japanese oyster - Crassostrea gigas ).
Oysters have a very low energy supply and contain mainly proteins; lipids are scarce but the cholesterol content requires moderate consumption. The hygienic-sanitary risk linked to the consumption of raw oysters from the wild or not guaranteed origin is not negligible.
Some oysters (not the ones mentioned above) produce pearls and are widely used in the jewelery industry.
Description
As anticipated, the oysters are molluscs belonging to the Bivalve Class; the common ones have an external shell (valve) that protects the soft part. Externally, this sort of armor is wrinkled, lamellar, irregular, of a white - shaded gray color; internally it appears smooth and mother-of-pearl in color. The shell of the oysters, besides shielding the animal, is essential for anchoring it on the rocks. The lower segment is larger and concave, while the upper segment is flat. THE
The inner body of the common oysters is discoid, gray-beige and greenish in color, bordered by small cilia and attached to the inside of the flat valve. Outside, the shell acts as an adhesive on solid bodies (rocks, poles, wrecks etc.). The common oysters are medium in size, just over 10cm, while the C. gigas reaches decidedly larger dimensions and presents a very strong polymorphism, that is a remarkable irregularity of the overall shape; however, the anatomical organization is similar to that of common oysters.
Outline of biology
Oysters live in salty or brackish waters, possibly rich in organic residues and small organisms, which are fed by filtering water (similar to mussels). They colonize bathymetric variables ranging from 0 to tens of meters deep (some remain uncovered at low tide) and are present in seas all over the world.
At European level, Specie edulis is cultivated / bred especially in Italy, France and Croatia. In addition to the Mediterranean basin, common oysters are also present in the Atlantic Ocean, in the North Sea.
In parallel, the Pacific oysters (which, as the term suggests, are typical of that area) have reached and colonized both the Atlantic Ocean and the Mediterranean Sea. They have a proliferation and a higher yield than common oysters and this is determining their commercial imposition compared to their European cousins.
Oysters in the kitchen
Oysters owe their fame to the unmistakable taste perceived in "raw" recipes. In reality, oysters are not the only bivalve molluscs that lend themselves to such consumption; also mussels, scallops, fasolari, clams etc. they represent real delicacies.
As far as oysters are concerned, probably the only useful observation is that concerning the cleaning of raw food . The breeding ones are already sufficiently clean oysters; however, sometimes it is still necessary to apply an energetic brush to the shell to remove sand residues and any algae. This is a particularly important procedure since, whether in the raw consumption (where it is still served in the shell), or in the one that involves cooking (sauté, au gratin, etc.), the presence of impurities can compromise its pleasantness. Moreover, for raw oysters, it is also essential to have a good technique for opening the valves; this process is carried out by means of a special tool consisting of a steel blade (not sharp), drop-shaped and provided with a handle. Holding the oysters with a hand appropriately protected by the characteristic metallic glove, proceed with the identification of the point where the two shells are joined. Right there, with energy, it will be necessary to insert the blade and force the opening of the valves using the lever of the instrument. WARNING! For the most inexperienced it is advisable to check that, in the opening phase, the shell splinters do not fall inside the mollusc. Once the opening of the oysters is complete, it is then sufficient to season them with black pepper (or white, depending on taste) and lemon juice; for some it is also appreciated the combination with a bit of caviar and / or a drop of extra virgin olive oil; ABSOLUTELY to avoid adding salt! The sea water contained within the oysters, in fact, is already sufficient to give flavor to the dish.
Obviously, for raw consumption, the choice of a good and safe source of supply is decisive, which, in addition to ensuring the freshness and organoleptic quality of the oysters, will guarantee the complete healthiness of the shellfish, protecting the consumer from food poisoning. Some examples of contractable diseases by consuming raw contaminated oysters are: HAV viral hepatitis, cholera, gastroenteritis from faecal coliforms etc. Obviously, at the time of purchase, the oysters must be alive, then sealed, and give off a pleasant scent of sea and fresh seaweed. In the event of any doubt about the state of conservation, avoid them.
Oyster sauté is an almost banal preparation; after having brushed them, fry them with oil and garlic, blending with white wine as soon as the shells begin to open. From there, wait for it to hatch completely (less evident than that of the clams or mussels) and add ground pepper and fresh parsley.
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Nutritional values (per 100 g of edible portion)
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Gratinated oysters are prepared by opening the mollusc (as described above) and lightly smudging it with a "panure" flavored with EVO oil, pepper, fresh parsley and garlic. The addition of little bottarga, capers, anchovies and cubes of fresh tomato is very pleasant. For some, a pinch of grated pecorino cheese does not hurt. The cooking should be done in the oven (or in salamander) at very high temperatures (> 200 ° C) for a few minutes (from 5 to 10).
Nutritional characteristics
Oysters are foods that can be defined as having a low energy intake. Suitable for feeding against overweight, however they have a big limit to the portions; this is due to the reduced digestibility of the food which, in case of excess, could be the cause of annoying adverse reactions (gastric cramps and vomit, not to be confused with the symptoms of a possible food poisoning). The oysters are therefore not suitable for those who suffer from digestive problems (eg hypo and hyperchlorhydria).
We also remind that oysters are potentially allergenic foods and that their consumption is not recommended in: pregnancy, lactation and early childhood.
It should also be remembered that oysters are molluscs capable of retaining high concentrations of sea water; this characteristic gives it a very high sodium content, an element potentially responsible for the onset or aggravation of arterial hypertension. Oysters are not suitable for the low-sodium diet, so they should be excluded from the hypertension diet, which may include them only occasionally.
From the point of view of energy nutrients, oysters are distinguished by the prevalence of proteins (with high biological value) compared to sugars (the latter present in a few grams of glycogen) and to fats (of the three, the most deficient element).
Oysters are also rich in cholesterol; this aspect contextualizes them in the diet of the healthy subject but precludes its use in the diet of suffering from hypercholesterolemia.
As far as the mineral salts are concerned, as well as sodium, the oysters are very rich in iron (important to prevent iron deficiency anemia especially in fertile women) and calcium (useful for bone metabolism especially in growing and elderly people).
From a vitamin point of view, oysters contain good concentrations of retinol equivalent (vit. A). It is interesting to learn that in some types of oysters (for example, Olimpia) good amounts of vitamin C have been detected (38mg / 100g - not mentioned in the table).
