Jonathan Swift is quoted as having said, “He was a bold man that first ate an oyster”, but evidence of oyster consumption goes back into prehistory, evidenced by oyster middens found worldwide. Oysters were an important food source in all coastal areas where they could be found, and oyster fisheries were an important industry where they were plentiful. Over-fishing and pressure from diseases and pollution have sharply reduced supplies, but they remain a popular treat celebrated in oyster festivals in many cities and towns.
It was once assumed that oysters were only safe to eat in months with the letter ‘r’ in their English and French names. This myth is based in truth, in that in the Northern Hemisphere, oysters are much more likely to spoil in May, June, July, and August.
Oysters are an excellent source of zinc, iron, calcium, and selenium, as well as vitamin A and vitamin B12. Oysters are low in food energy; one dozen raw oysters contains 110 kilocalories (460 kJ). Oysters are considered most nutritious when eaten raw.
Traditionally, oysters are considered to be an aphrodisiac, partially because they resemble female sex organs. A team of American and Italian researchers analyzed bivalves and found they were rich in amino acids that trigger increased levels of sex hormones. Their high zinc content aids the production of testosterone.
Dietary supplements may contain calcium carbonate from oyster shells, though no evidence shows this offers any benefits beyond what calcium may offer.
Selection, preparation and storage
Unlike most shellfish, oysters can have a fairly long shelf life of up to four weeks. However, their taste becomes less pleasant as they age. Oysters should be refrigerated out of water, not frozen, and in 100% humidity. Oysters stored in water under refrigeration will open, consume available oxygen, and die.
Oysters must be eaten alive, or cooked alive. The shells of live oysters are normally tightly closed or snap shut given a slight tap. If the shell is open, the oyster is dead, and cannot be eaten safely. Cooking oysters in the shell kills the oysters and causes them to open by themselves. Traditionally, oysters that do not open have been assumed to be dead before cooking and therefore unsafe. However, according to at least one marine biologist, Nick Ruello, this advice may have arisen from an old, poorly researched cookbook’s advice regarding mussels, which has now become an assumed truism for all shellfish. Ruello found 11.5% of all mussels failed to open during cooking, but when forced open, 100% were “both adequately cooked and safe to eat.”
Oysters can be eaten on the half shell, raw, smoked, boiled, baked, fried, roasted, stewed, canned, pickled, steamed, or broiled, or used in a variety of drinks. Eating can be as simple as opening the shell and eating the contents, including juice. Butter and salt are often added. In the case of oysters Rockefeller, preparation can be very elaborate. They are sometimes served on edible seaweed, such as brown algae.
Care should be taken when consuming oysters. Purists insist on eating them raw, with no dressing save perhaps lemon juice, vinegar (most commonly shallot vinegar), or cocktail sauce. Upscale restaurants pair raw oysters with a home-made Mignonette sauce, which consists primarily of fresh chopped shallot, mixed peppercorn, dry white wine and lemon juice or sherry vinegar. Like fine wine, raw oysters have complex flavours that vary greatly among varieties and regions: sweet, salty, earthy, or even melon. The texture is soft and fleshy, but crisp on the palate. North American varieties include: Kumamoto and Yaquina Bay from Oregon, Malpeque from Prince Edward Island, Canada, Blue Point from Long Island, New York, and Cape May oysters from New Jersey. Salinity, mineral, and nutrient variations in the water that nurtures them influence their flavour profile.
Oysters can contain harmful bacteria. Oysters are filter feeders, so will naturally concentrate anything present in the surrounding water. Oysters from the Gulf Coast of the United States, for example, contain high bacterial loads of human pathogens in the warm months, most notably Vibrio vulnificus and Vibrio parahaemolyticus. In these cases, the main danger is for immunocompromised individuals, who are unable to fight off infection and can succumb to septicemia, leading to death. Vibrio vulnificus is the most deadly seafood-borne pathogen, with a higher case-to-death ratio than even Salmonella enterica.
Special knives for opening live oysters, such as this one, have short and stout blades and the best have a downward curve at the tip.
Fresh oysters must be alive just before consumption or cooking. There is only one criterion: the oyster must be capable of tightly closing its shell. 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 be closed. These make a distinctive noise when tapped, and are known as ‘clackers’.
Opening oysters requires skill. The preferred method is to use a special knife (called an oyster knife, a variant of a shucking knife), with a short and thick blade about 5 cm long.
While different methods are used to open an oyster (which sometimes depend on the type), the following is one commonly accepted oyster-shucking method.
- Insert the blade, with moderate force and vibration if necessary, at the hinge between the two valves.
- Twist the blade until there is a slight pop.
- Slide the blade upward to cut the adductor muscle which holds the shell closed.
Inexperienced shuckers can apply too much force, which can result in injury if the blade slips. Heavy gloves are necessary; apart from the knife, the shell itself can be razor sharp. Professional shuckers require less than three seconds to open the shell.
If the oyster has a particularly soft shell, the knife can be inserted instead in the ‘side-door’, about halfway along one side where the oyster lips widen with a slight indentation.
Opening or “shucking” oysters has become a competitive sport. Oyster-shucking competitions are staged around the world. Widely acknowledged to be the premiere event, the Guinness World Oyster Opening Championship is held in September at the Galway Oyster Festival. The annual Clarenbridge Oyster Festival ‘Oyster Opening Competition’ is also held in Galway, Ireland.
The oyster is considered by some ethicists to be an appropriate food choice for those concerned with animal rights, arguing it is acceptable to eat oysters due to their lack of a central nervous system and the generally sustainable and environmentally friendly way in which they are raised and harvested.
One common ethical objection to the consumption of animals is that their cultivation is environmentally harmful. Regarding environmental impact, 95% of oysters are sustainably farmed and harvested (other bivalves are frequently harvested by harmful dredging), feed on plankton (very low on the food chain), and in fact improve the marine environment by removing toxins. As such, farmed oysters are listed as a “Best Choice” (highest rating) on the Seafood Watch list.
The view that oysters are acceptable to eat, even by strict ethical criteria, has notably been propounded in the seminal 1975 text Animal Liberation, by philosopher Peter Singer. However, subsequent editions have reversed this position (advocating against eating oysters). Singer has stated he has “gone back and forth on this over the years”, and as of 2010, says, “while you could give them the benefit of the doubt, you could also say that unless some new evidence of a capacity for pain emerges, the doubt is so slight that there is no good reason for avoiding eating sustainably produced oysters”.