Oyster

The name oyster is used for a number of different groups of mollusks which grow for the most part in marine or brackish water. Inside a usually highly calcified shell is a soft body. The gills filter plankton from the water. Strong adductor muscles are used to hold the shell closed.

Oysters are highly prized as food, both raw and cooked

Perhaps the definitive work on oysters as food is Consider the Oyster, by M. F. K. Fisher.

True oysters

The "true oysters" are the members of the family Ostreidae, and this includes the edible oysters, which mainly belong to the genera Ostrea, Crassostrea, Ostreola or Saccostrea. Examples are the Edible Oyster, Ostrea edulis (others are just as edible); the Olympia Oyster Ostreola conchaphila; Wellfleet oyster and the Eastern Oyster Crassostrea virginica.

Oysters as edibles

Oysters can be eaten raw, or smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, or broiled (grilled). Preparation can be as simple as opening the shell, while cooking can be as spare as adding butter and/or salt, or can be very elaborate.

Oysters are low in calories, one dozen raw oysters contain approximately 110 calories (460 kJ), rich in iron and high in calcium and vitamin A.

Like all shellfish, oysters have an extremely short shelf-life, and should be fresh when consumed. Precautions should be respected when eating them (see below). Purists insist on eating oysters raw, with no dressing save perhaps lemon juice or vinegar. Raw oysters are regarded like wines in that they have complex flavors that vary greatly among varieties and regions: some taste sweet, others salty or with a mineral flavor, or even like melon. The texture is soft and fleshy, but crisp to the tooth.

Oysters are generally an expensive food in places where they aren't harvested, and often they are eaten only on special occasions, such as Christmas. Whether oysters are predominantly eaten raw or cooked is a matter of cultural preference. In the United States today, oysters are usually cooked before consumption; canned smoked oysters are widely available as preserves with a long shelf life. Raw oysters were, however, once a staple food along the East Coast of the US, and are still easily found in states bordering the ocean. Oysters are nearly always eaten raw in France.

Fresh oysters must be alive just before consumption. There is a simple criterion: oysters must be tightly closed; oysters that are already open are dead and must be discarded. To confirm if an open oyster is dead, tap the shell. A live oyster will close and is safe to eat. Opening oysters requires skill, for live oysters, outside of the water, shut themselves tightly with a powerful muscle. The generally used method for opening oysters is to use a special knife (called a shucking knife), with a short and thick blade, inserting the blade (with some moderate force and vibration if necessary) at the hinge in the rear of the shell, and sliding it upward to cut the adductor muscle (which holds the shell closed). Inexperienced cooks tend to apply excessive force, which may result in injuries if they slip; this is said to be a significant cause of domestic accidents in the Christmas season in France.

An alternative to opening raw oysters before consumption is to cook them in the shell – the heat kills the oysters and they open by themselves. Cooked oysters are savory and slightly sweet-tasting, and the varieties are mostly equivalent.

A piece of folk wisdom concerning oysters is that they are only safe to eat in months containing the letter r. This is because oysters spawn in the warmer months, from roughly May to August in the Northern Hemisphere. They are safe to eat at all times of the year, although their flavor when eaten raw can be somewhat watery and bland during spawning season. Oysters from the Gulf of Mexico spawn throughout the year, but are delicious cooked or raw.

Oysters are sometimes cited as an aphrodisiac. It is disputed whether this is true. If there is such an effect, it may be due to the soft, moist texture and appearance of the oyster; it may also be due to their high zinc content. Another joking theory states, "If you can get a woman to eat a raw oyster, you can get her to do anything!" referring to their visual nature, unappealing for some people.

History

Within the United Kingdom, the town of Whitstable in the county of Kent is particularly noted for oyster farming from beds on the Kentish Flats that have been used since Roman times. Similarly the seaside resort of Cancale in France is noted for its oysters which also date from Roman times.

In the early nineteenth century, oysters were very cheap and were mainly eaten by the working classes in steak and oyster pies. However, increasing demands from the rapidly-growing cities led to many of the beds running short. To increase production, foreign varieties were introduced and this soon brought disease which, combined with pollution, resulted in oysters becoming rare. This rarity increased prices leading to their current status as a delicacy.

In the United Kingdom, the native variety is still held to be the finest, taking five years to mature and protected by an Act of Parliament during the May-August spawning season. The current market is dominated by the larger Pacific oyster and rock oyster varieties which are farmed all year round.

Pearl oysters

All oysters (and, indeed, many other bivalves) can secrete pearls, but those from edible oysters have no market value. The Pearl Oysters come from a different family, the Pteriidae (Winged Oysters). Both cultivated pearls and natural pearls are obtained from these oysters, though some other mollusks, for example freshwater mussels, also yield pearls of commercial value. The largest pearl-bearing oyster types is the Pinctada maxima, which is roughly the size of a dinner plate. Not all oysters produce pearls. In fact, in a haul of three tonnes of oysters, only around three or four oysters produce perfect pearls.

These oysters, and other mollusks, produce pearls by covering an invading piece of grit with nacre (or as most know it, mother-of-pearl). Over the years, the grit is covered with enough nacre to form what we know as a pearl. There are many different types and colours and shapes of pearl, but this depends on the pigment of the nacre and the shape of the piece of grit being covered over.

Pearls can also be cultivated by pearl harvesters placing a single piece of grit, usually a piece of polished mussel shell, inside the oyster. In three to six years, the oyster has produced a perfect pearl. These pearls are not as valuable as natural pearls, but look exactly the same.

Dermo

"Dermo" ( Perkinsus marinus) is marine disease of oysters, caused by a protozoan parasite. It is a prevalent pathogen of oysters, causing massive mortality in oyster populations and poses a significant economic threat to the oyster industry.

Other molluscs named "oyster"

A number of other molluscs not falling into either of these groups have common names that include the word "oyster", usually because they either taste or look like oysters, or because they yield noticeable pearls. Examples include:

• the family Spondylidae, the Thorny Oysters;
• the Pilgrim oyster, a kind of scallop.
• the Saddle oyster (Anomia ephippium)
• the Mountain oyster, not an oyster at all but the inner testicles of a bovine animal.