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The common name oyster is used for a number of different groups of bivalve mollusks, most of which live in marine habitats or brackish water. The shell consists of two usually highly calcified valves which surround a soft body. Gills filter plankton from the water, and strong adductor muscles are used to hold the shell closed.
Some types of oysters are highly prized as food, both raw and cooked. Other types, such as pearl oysters, are not widely eaten.
Oysters can be eaten half shelled, raw, smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, broiled (grilled) or used in a variety of drinks. Preparation can be as simple as opening the shell and adding butter and/or salt, or can be very elaborate.
Oysters are low in food energy; one dozen raw oysters contain approximately 110 kilocalories (460 kJ), and are rich in zinc, iron, calcium, and vitamin A.
Unlike most shellfish, oysters can have a fairly long shelf-life: up to around two weeks; however, they should be consumed when fresh, as their taste reflects their age. For maximum shelf life, oysters should be stored out of water in refrigeration but not frozen and in 100% humidity. Oysters stored in water under refrigeration will open, utilize the small reserves of oxygen and die. Precautions should be taken when consuming them (see below). Purists insist on eating oysters raw, with no dressing save perhaps lemon juice, vinegar (most commonly shallot vinegar) , or cocktail sauce. Raw oysters are regarded like wines in that they have complex flavours that vary greatly among varieties and regions: some taste sweet, others salty or with a mineral flavour, or even like melon. The texture is soft and fleshy, but crisp to the tooth. This is often influenced by the water that they are grown in with variations in salinity, minerals, and nutrients.
Oysters are generally an expensive food in places where they are not 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 personal preference. In the United States today, oysters are most often cooked before consumption, but there is also a high demand for raw oysters on the half-shell (shooters) typically served at oyster bars. Canned smoked oysters are also widely available as preserves with a long shelf life. Raw oysters were once a staple food for the poor in many countries with coastal access such as the United Kingdom and along the East Coast of the US and are thus still easily found in any areas bordering a sea or ocean. Oysters are commonly eaten raw in France in bars and as a 'bar fast food' but the home use tends to be mixed with a large usage in cooking - steamed or in paella or soups.
Fresh oysters must be alive just before consumption. There is a simple criterion: oysters must be capable of closing the shell tightly. Any open oysters should be tapped on the shell: a live oyster will close up and is safe to eat. Oysters which are open and unresponsive are dead, and must be discarded. Some dead oysters, or oyster shells which are full of sand may also be closed, but they will make a distinctive noise when tapped: they are known as "clackers" for this reason.
Opening oysters requires skill, for live oysters, outside of the water, tend to shut themselves tightly with a powerful muscle thus sealing in their fluids. The generally used method for opening oysters is to use a special knife (called an oyster knife, a variant of a shucking knife), with a short and thick blade about 2 inches long.
The blade needs to be inserted (with some moderate force and vibration if necessary) at the hinge in the rear of the shell. with the blade inserted slightly you need to twist until a slight pop is heard/felt. Then the blade should be slid upward to cut the adductor muscle (which holds the shell closed). Inexperienced shuckers tend to apply excessive force, which may result in injuries if the blade slips. A heavy glove should always be worn: if you don't cut yourself with the knife you can just as easily cut yourself on the oyster shell itself, which can be razor sharp.
A good demonstration of the opening technique is available here. There is also a second way in, referred to as the "sidedoor", which is about halfway along one side where the lips of the oyster widen so there is a slight indentation where a knife may successfully be inserted. This is generally a better way to open an oyster when it is a "crumbler" (i.e. one with a particularly soft shell either due to drills or the amount of calcium in the water). Either way, however, can be tricky when an oyster's shell is in such a poor condition.
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 slightly sweet-tasting and considered savoury, and all the different varieties are mostly equivalent.
A piece of folk wisdom concerning oysters is that they are best to eat in months containing the letter r, as illustrated by the famous phrase: "oysters 'r' in season." This is because oysters spawn in the warmer months, from roughly May to August in the Northern Hemisphere, and their flavour when eaten raw can be somewhat watery and bland during spawning season; additionally their meats are much reduced in size. Oysters from the Gulf of Mexico spawn throughout the year, but are delicious cooked or raw to the oyster connoisseur.
Oysters are sometimes cited as an aphrodisiac. It is disputed whether this is true. According to the Telegraph of London a team of "American and Italian researchers analysed bivalve molluscs - a group of shellfish that includes oysters - and found they were rich in rare amino acids that trigger increased levels of sex hormones." 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.
How much does one cup of oysters weigh?
Estimated US cup to weight equivalents:
|225 grams||8 ounces|
Every ingredient has a cups to ounces or grams conversion table. Search for the ingredient, cup to weight conversions are at the end of each ingredient page.
Seasonal Information: Oysters
This information is specifically for countries in the northern temperate zone of the Northern Hemisphere; particularly the United Kingdom, however it should be applicable for northern USA, northern Europe, Canada, Russia, etc.
Oysters are at their best and in season during the following months: October, November, December, January, February & March.