The oyster, which is a bivalve mollusc (a valve, each of the two parts of their shell), is an excellent source of vitamin B12 , copper , iron , zinc , as well as several other nutrients. In addition, the lipid content of the oyster, slightly higher than that of other seafood, gives it the advantage of being a good source of vitamins A and D , these vitamins being soluble only in oil. .

Active ingredients and properties

The active ingredients of the oyster have not been the subject of specific studies. However, we note a few studies showing interesting results on the benefits of eating fish and seafood. First, a study of more than 14,000 women showed that the more they eat fish and seafood. sea, the lower their risk of colorectal cancer ¹ . Another study, carried out with Chinese, showed that the weekly consumption of at least one meal of fish or seafood would be associated with a lower risk of fatal myocardial infarction , compared to a lower consumption ². At present, the beneficial effects of the consumption of these marine products cannot be associated with a particular active ingredient; clinical studies are necessary to identify the components involved. On the other hand, the presence of omega-3 fatty acids in fish and seafood could have an important role to play.

Omega-3 fatty acids . The oyster contains eicosapentaenoic acid ( EPA ) and docosahexaenoic acid ( DHA ), two fatty acids from the omega-3 family. The oyster is a very good source of these two fatty acids, providing an amount comparable to certain fatty fish such as mackerel and sardines. Omega-3 fatty acids act as precursors of chemical messengers promoting the proper functioning of the immune, circulatory and hormonal systems. Several epidemiological and clinical studies have shown that the consumption of omega-3 fatty acids (mainly from fatty fish) could exert favorable effects on cardiovascular health., including reduced mortality from cardiovascular disease ³ . These fatty acids are known to reduce blood pressure , blood triglycerides and the formation of blood clots .

The fat content of the oyster is somewhat higher than that of most other seafood, hence the particularly high amount of omega-3 fatty acids it contains. Even if the optimal amounts of omega-3 fatty acids to consume have not been firmly established, scientific evidence shows that the daily consumption of 500 mg to 1,800 mg of EPA and DHA would make it possible to benefit from the related benefits. ⁴ . The consumption of 100 g of oysters (about two medium raw oysters) provides almost 1,400 mg. For comparison, the oyster contains 1.5 times less EPA and DHA than salmon, a fatty fish.

Most important nutrients

See the meaning of the nutrient source classification symbols

 Phosphorus. The oyster is an excellent source of phosphorus, the second most abundant mineral in the body after calcium (see our Phosphorus nutrient fact sheet ). Aside from its essential role in the formation of bones and teeth, it participates, among other things, in the growth and regeneration of tissues. It helps to keep the pH of the blood normal. It is also one of the constituents of cell membranes.

 Iron. The oyster is an excellent source of iron. A portion of four cooked oysters provides 50% and 100% respectively of the daily iron requirements of women and men, the latter having different needs for this mineral. Iron contributes to the transport of oxygen in the blood and the formation of red blood cells. It also plays a role in the production of new cells, hormones and neurotransmitters. An iron deficiency leads to anemia, causing weakness, fatigue and sometimes depression.

 Zinc. The oyster is an excellent source of zinc. Zinc is involved in particular in immune reactions, in the production of genetic material, in the perception of taste, in the healing of wounds and in the development of the fetus. Zinc also interacts with sex and thyroid hormones. In the pancreas, it participates in the synthesis (production), the storage and the release of insulin.

 Copper. The oyster is an excellent source of copper. As a constituent of several enzymes, copper is necessary for the formation of hemoglobin and collagen (protein used for the structure and repair of tissues) in the body. Several copper-containing enzymes also help the body’s defense against free radicals.

 Selenium. The oyster is an excellent source of selenium. Selenium works in concert with one of the main antioxidant enzymes, preventing the formation of free radicals in the body. It also helps to convert thyroid hormones to their active form.

 Vitamin B2 . The oyster is an excellent source of vitamin B2, also known as riboflavin. This vitamin plays a role in the energy metabolism of all cells, in addition to contributing to the growth and repair of tissues, the production of hormones and the formation of red blood cells.

 Vitamin B12. The oyster is an excellent source of vitamin B12; a single cooked oyster provides three times the recommended nutritional intake. Also called cobalamin , vitamin B12 helps in the production of new cells, contributes to the maintenance of nerve cells, makes folic acid active and participates in the metabolism of certain fatty acids and amino acids.

 Vitamin B3. The oyster is a good source of vitamin B3, also called niacin . It takes part in many metabolic reactions and contributes especially to the production of energy starting from carbohydrates, lipids, proteins and alcohol which we ingest. Niacin also participates in the DNA formation process.

 Vitamin A. The oyster is a good source of vitamin A. This vitamin is one of the most versatile, playing a role in several body functions. Among other things, it promotes the growth of bones and teeth, keeps skin healthy and protects against infections. In addition, it plays an antioxidant role and promotes good vision.

Manganese. The oyster contains manganese. Manganese helps several enzymes in their functions, thus facilitating a dozen different metabolic processes. It also participates in the prevention of damage caused by free radicals. There is no recommended nutritional intake for manganese, but sufficient intake.

Iodine. The oyster contains iodine. This is part of the composition of thyroid hormones, necessary for the regulation of growth, development and metabolism. The exact value for oyster iodine content is not available from the Canadian Nutrient File .

Pantothenic acid. The oyster contains pantothenic acid, also called vitamin B5. This acid plays a key role in the energy use of the food we eat. It also participates in several stages of the synthesis of steroid hormones, neurotransmitters and hemoglobin. There is no recommended nutritional intake for pantothenic acid (vitamin B5), but sufficient intake.

Vitamin D. The oyster contains vitamin D. A single oyster alone fills 40% of sufficient intakes of this vitamin. Vitamin D is closely linked to bone health, making calcium and phosphorus available in the blood. It also plays a role in the maturation of cells, among others the cells of the immune system. There is no recommended nutritional intake for vitamin D, but sufficient intake.

Source: Health Canada. Canadian Nutrient File , 2005.

Precautions

The oyster is a food rich in purines, precursor substances of uric acid. Thus, people suffering from gout must limit their consumption in order to prevent the onset of seizures. In people with this condition, there is an abnormally high amount of uric acid in the blood, causing specific symptoms, such as joint pain. The purines in certain foods help to further increase the concentration of uric acid in the blood, which is why it is important for people with gout to limit their consumption.

Fish and seafood are among the nine most common food allergens in Canada. According to the Canadian Food Inspection Agency, it is possible that a person with an allergy to a given fish or seafood is also allergic to other species belonging to the same type (fish, crustacean or mollusk) , without necessarily being allergic to other types. For example, a person with an oyster allergy could also be allergic to clams, both of which are molluscs. It is still strongly recommended to people allergic to these foods to consult an allergist before introducing new ones in their diet.

If you eat raw oysters, you should know that bacteria multiply at a phenomenal rate in dead molluscs, hence the capital importance of ensuring that these oysters are alive and well (see the Good section). to choose).

The pregnant women and breastfeeding should avoid eating raw oysters, given the risks of foodborne illness that can have serious consequences for the fetus or baby. Particular attention should also be paid to cross-contamination between raw seafood and other foods.

Requiring no tools, the harvesting of molluscs on beaches and sandbanks by our prehistoric ancestors would have long preceded hunting and fishing, at least in coastal or lake regions. It was enough to bend down to pick them up and, in a few minutes, we had enough to support the whole family, even the tribe.

Among the products of the sea, the oyster has always occupied a place of choice, except among the Egyptians and the Hebrews, who considered it as an impure food. The Greeks, on the contrary, ate it with pleasure, while the Romans made it a real passion. They knew, from the Greeks, the conditions necessary for its growth and raised it in parks from spat (oyster embryos) taken from the sea. At the time of the conquest of Gaul, whose coasts abounded with this mollusc, this breeding constituted one of the main resources of the Empire.

The two stages of oyster farming

After four centuries of Roman occupation, the Gauls had reached a very high degree of perfection and technical expertise in the culture of the oyster and their products were renowned throughout the Roman world. Much of the harvest was brined in barrels and shipped to all corners of the Empire to feed the soldiers.

During the Middle Ages and the Renaissance, the fresh oyster was very popular with the wealthy in Europe, including in cities far from the coast, as evidenced by the remains found in Geneva. In France and England, it was eaten cooked, in the form of a meatless stew. Moreover, between the XIV ^th  and the XVIII ^th  century, there is no mention in the culinary works of its consumption in the raw state, probably because she could not stand the long commute from the sea to cities inside. The first settlers, who will be impressed by the size, abundance and excellence of the oysters they find along the North American coast, will cook them according to the recipes of their native country. century, on the other hand, it is common to consume it raw simply seasoned with a little pepper.

However, the uncontrolled looting this resource, combined with damage caused by storms, lead to a considerable decrease in inventories, both Europe and America, so that, between the middle and the end of XIX ^th  century, each of them aside, the French and the Americans will develop oyster farming: oyster farming. Depending on the species and the region, the oyster raised in “parks” takes two to seven years before reaching a size allowing it to be marketed.

Oyster “grands crus”

Today, cultivated species represent 95% of trade in oysters worldwide. They belong to two genera, different by their mode of reproduction: Ostrea (flat oysters) and Crassotrea (hollow oysters); each genus includes hundreds of species. Only a few are of economic importance, in particular:
– the Pacific oyster ( Crassotrea gigas ), large in size and native to Japan, it is now the most cultivated species in the world;
– the Kumamoto ( Crassotrea sikamea ), closely related to the Pacific oyster, but much smaller in size and with a milder flavor;
–the Atlantic oyster ( Crassotrea virginica ), one of whose shells has a clearly rounded hollow, is sometimes called American because it is native to the east coast of North America;
– European ( Ostrea edulis ), a small flat oyster with a particularly sweet flavor, one of the most famous varieties of which is Belon , named after a bay of Brittany (but this variety is also cultivated in North America) .

Climate, water temperature and degree of salinity, the nature of the bottom where it is high and the plankton it consumes contribute to the flavor of the oyster , which varies accordingly and which has given rise to regional “vintages” : green from Marennes, bouzigues from Languedoc, cantals from Manche (France), Whitstable, Helford, Colchester from Great Britain and, in the United States, Blue Point and Cape Cod. In Canada, the Caraquet and Malpèque from the Maritime provinces are of the Atlantic species. While some prefer the salty taste of Malpeque, both are highly prized by Canadian consumers, who buy all fresh stocks, and are not processed or exported very little.

In order of importance, the main world producers are China, Japan, the United States, Korea and France. After the harvest, the oysters are packed in wooden or cardboard boxes and shipped to the markets. They can live a few months in a humid environment and at a temperature just above the freezing point.

Choose well

To preserve themselves, fresh oysters must remain alive: their shell should be closed and intact. If it is open, hit it gently; live oysters will close. Otherwise, leave them out. On the fishmonger’s stall, oysters should not be buried in ice, but placed on its surface, rounded side down. Their aroma should recall that of the sea breeze. In addition, they should be heavy for their size, a sign that they have preserved all their liquids and have not dried out.

In Canada, oysters are classified according to the shape of the shell and the relationship between length and width, characteristics that do not change the taste qualities of the flesh: commercial, normal, choice and luxury.

In Europe, depending on the special treatments applied at the end of the breeding cycle, varieties of gastronomic quality are called fine, special, clear or refined , the latter category representing the end of the end. As for the size, it is indicated by the letters P, M and G, or by numbers from 0 to 5, to which is added the “long” size for poorly formed shells.

The shelled oysters are presented in a mixture of water and their own liquids. In high season, they are found in bulk in the fish department. If prepackaged, check the expiration date. As for smoked oysters , they are found canned.

Until recently, the norm required that oysters should only be eaten in the months containing an “r”, because those picked in late spring and summer are less tasty. But current methods of cultivation and conservation make it possible to find at least certain varieties throughout the year .

Culinary dishes

Preparation

Wash and brush oysters only at the last minute. When opening an oyster, always place it with the rounded side down so that it preserves all of its internal liquids. To remove the shell, cut the abductor muscle using a knife intended for this use.

Culinary uses

• Raw  : simply season with pepper or a little lemon juice or a red vinegar in which will have macerated gray shallot.
• Steam  : allow four to seven minutes of cooking once the shell is open (about 10 minutes in total).
• In the oven  : at least 10 minutes at 230 ºC (450 ° F).

In terms of seasonings , the oyster goes perfectly with chives, parsley, thyme, garlic, dill, celery seed, cayenne pepper, nutmeg, paprika, curry, juice lemon or lime, Worcestershire sauce and tabasco.

In soup  : take shelled oysters, heat their juice to its maximum point without boiling, then place the oysters in it and poach them for a few minutes until their outline is close, which means that they are cooked; we will have previously heated whole milk to which we will have added a little butter or cream, as well as salt, pepper and a little nutmeg; pour the hot oysters, with their juice, into the hot milk, sprinkle with paprika – or another seasoning, to taste – and serve immediately (this soup must be prepared at the very last minute).

On the barbecue  : prepare a sauce with sesame oil, soy sauce, lime juice, a little grated ginger, garlic and a thinly sliced ​​green onion. Refrigerate two hours. Open the oysters, remove the upper shell, put them on the grill, add a little sauce in each of them and cook until the liquid boils. Serve immediately.

At tempura  : dip the oysters in a donut batter and cook them in a deep frying pan. Serve with vegetables cooked in the same way, a garnish of white radish and grated ginger and a sauce of dashi, soy sauce and mirin.

Rockefeller oysters  : prepare a puree by finely chopping spinach, a heart of lettuce, parsley, a few celery leaves and mixing them with softened butter, Worcestershire sauce, salt, pepper and, if desired, a few drops of Pernod. Put in the fridge to harden the puree. Garnish the oysters in their half-shell with a teaspoon of green mash, sprinkle with grated Parmesan cheese and breadcrumbs. Spread a good layer of coarse salt on a baking sheet, place the oysters in it and cook for eight minutes under the grill (placing them 8 cm from the heating element).

On pasta  : steam oysters until they open, making sure to place them so as to preserve their internal liquid. Extract the oysters and reserve their liquid as well as the cooking broth. Sauté garlic, green onion and red pepper for a few minutes in olive oil. Add the oyster liquid and the cooking broth and parsley. Thicken if desired with cornstarch. Add the oysters, reheat, serve over pasta and sprinkle with grated Parmesan.

In a stew  : cook the shelled oysters for three to five minutes in a little water to which we will have added a finely minced gray shallot. Drain and reserve the cooking water. Cut the oysters into pieces, put them back in the pan with the cooking water. Thicken with flour and add milk and a knob of butter, salt, pepper and season with a little tabasco. You can replace the milk with chicken broth or fish stock and the wheat flour with rice flour.

In a salad  : serve them steamed on a bed of young vegetables with a remoulade sauce.

Refrigerator  : one week at most for whole oysters, in a shallow container, covered with a damp cloth. Avoid keeping them in a plastic bag or airtight container.

Freezer  : shelled oysters presented in their juice can be frozen for three months. As their texture changes when frozen, it is best to cook them afterwards.

As is the case with other molluscs, oyster farming has little harmful effect on the environment, unlike their fishing, which is carried out by dragging and can have a negative impact on the habitats of several marine organisms.

In addition, scientists are very interested in the role that molluscs can play in the depollution of marine waters . In fact, only one of these organisms can filter from two to five liters of water an hour, taking in the process the phytoplankton found there to feed on it. However, it is precisely the proliferation of phytoplankton (which is made up of micro-algae) that is attributed today to eutrophication, that is to say oxygen depletion, of stagnant waters of lakes or marine berries, and the destruction of marine plants.

Formerly of great purity, the water of Chesapeake Bay, in Maryland, supported the life of numerous colonies of submerged plants which, in turn, contributed greatly to its sanitation. However, today, it is polluted by the proliferation of phytoplankton, and marine plants, lacking oxygen, can no longer develop there and now cover only 15% of the surface they once occupied. According to the researchers, this pollution is partly due to the almost complete disappearance of the huge oyster beds that lived there in the wild and filtered the water, ridding it of its phytoplankton overflow. In 1988, one of these researchers estimated that, 100 years ago, the oysters completely replaced the water in the bay in just six days, while

In addition to the efforts devoted to the reduction at the source of pollutants of terrestrial origin, the State of Maryland therefore set up a vast program of reintroduction of the American oyster in the bay and created, for strictly ecological purposes. , several sanctuaries reserved for this mollusk. Other such experiments are underway in the United States.