Celebrating oysters

Steeped in tradition, oysters are celebrated for their nutrition, taste, and environmental benefits. They are packed with vitamins and minerals and, as filter feeders, they are great for the environment. 

Have you heard – the world is your oyster?  In Shakespeare’s Merry Wives of Windsor, the character Falstaff says, “I will not lend thee a penny,” to which Pistol replies, “Why, then, the world’s mine oyster, Which I with sword will open.”  

You definitely don’t need a sword to open an oyster, but the world of oysters is fascinating. 

What are oysters?

Oysters are a type of bivalve – a class of mollusc with hard shells in two parts that includes clams, mussels and scallops. Bivalves filter the water around them, cleaning the water and helping with pollution. 

 Are oysters alive? 

Yes – as a type of shellfish, they are alive, though they don’t move much. They are often found in large groups called reefs or beds, which provide protection for various species of fish, crabs, and other marine life. 

Types of oysters:

Globally, there are more than 200 varieties, with around 12 species being farmed commercially. 

The leading farmed species include: 

•      European flat or native oyster
•      Pacific, Japanese cupped or rock oyster
•      Kumamoto oyster
•      Atlantic oyster
•      Sydney rock oyster and New Zealand rock oyster
•      Olympia oyster

How do oysters make pearls?

Pearls are formed when an irritant (often a parasite) gets trapped in the mollusc.  

The irritant is coated with layers of aragonite and conchiolin which are the same materials that oysters use to build their shells. The pearl is then coated in nacre (mother of pearl), giving it the shine. 

All bivalves can make pearls, but not all can produce the nacre that makes pearls so precious.   

Are oysters nutritious?

Yes. Low in calories and high in vitamins and essential nutrients, they are a very nutritious food source. 

Containing high amounts of zinc, vitamin B12, iron, vitamin E, and calcium, oysters are a good source of omega-3 fatty acids, which regulates inflammation and support brain and heart health. 

How many calories in raw oysters? 

100 grams of raw oysters contain 51 calories, nearly 6 grams of protein, and about 2 grams of fat. They can have more calories when cooked, depending on the cooking method and any extra ingredients. 

Farmed oysters

How do oyster farms work? 

Oysters are very adaptable, making them a good species for seafood farming. And depending on the species, they usually take one to three years to mature.  

Farmed oysters begin life in a hatchery and are moved to nursery tanks or ponds to grow. When mature enough to attach themselves to a surface, they are moved to the sea. Once permanently attached to a surface, they are known as “spat”. 

Oysters are farmed in two main ways: bottom culture and off-bottom culture.  

With bottom culture, the sea floor itself is used as the base for the farm. Oysters need a surface to attach themselves to – in bottom culture, this is often an existing oyster bed. When mature, they are harvested like wild oysters, using “fishing” techniques like dredging. 

Off-bottom cultured oysters are grown off the sea floor, kept in a controlled, floating environment such as a cage or a tray, or stuck to ropes, and then collected by hand when they mature. 

Is oyster farming environmentally friendly?

Oysters are filter feeders, making them extremely environmentally friendly. Because they clean the water around them as they eat, oyster farms leave the surrounding water cleaner than it would’ve been otherwise. Other benefits include protecting shorelines, stabilising the sediment and creating a habitat for other organisms. 

Because oysters bind carbon in their shells, shellfish farming is a contributor in the fight against climate change and ocean acidification. 

What do oysters eat?

Like other bivalves, oysters eat phytoplankton or algae filtered from the water around them. Filtering up to 150 litres of water a day, they help to clean their environment. And because any toxins present in the water are deposited in the sediment, they are not contaminated during their filter feeding. 

When are oysters in season?

In the northern hemisphere, the old rule of thumb is to only eat shellfish in months with an ‘r’. This means they shouldn’t be eaten in May, June, July, or August. Oysters reproduce in the summer months, making their flesh too soft to eat. However, rock oysters are in season all year. 

Can you eat farmed oysters?

Farmed oysters are safe to eat and environmentally friendly, with farms often having a positive impact on the environment around them. 

Most oysters found in supermarkets and restaurants are farmed because wild populations are heavily overfished in many places, making farmed oysters the more sustainable choice. In addition to meeting the strictest environmental standards, oysters from ASC-certified farms are grown in a socially responsible manner. 

How to eat oysters

Oysters are very versatile and are classically eaten on the half shell. They are freshly opened, or shucked, with a special knife and served in half of their shell on a bed of ice. Raw oysters can be eaten just as they are. They can also be enjoyed with a splash of Tabasco sauce, a squeeze of lemon, or a French shallot vinegar. 

Cooking oysters 

Oysters can also be steamed, grilled, or fried. One way is to top them with a mix of breadcrumbs, parmesan, and fresh herbs, and grill for 2-3 minutes. They are also pan fried or eaten in an Irish steak and oyster pie. 

Are oysters alive when you eat them? 

Oysters are eaten raw, either while still alive or freshly killed through the shucking process and usually served on ice, ensuring they are still fresh when eaten. 

Dead oysters should not be eaten raw – discard any with cracked or damaged shells or that aren’t tightly closed. If they are open and don’t close when touched, they should also be thrown away. These are indications that the oyster inside is no longer living. 

How to shuck an oyster 

10 simple steps to shuck an oyster: 

1. Scrub the shell with a firm brush under cold running water 
2. Wrap your hand thickly in a tea towel for protection  
3. Hold the oyster firmly in the towel 
4. Place the cupped shell in the palm of your hand, with the hinge facing you.  
5. There’s a small gap in the hinge of the shell. Insert a shucking knife here, or a small, strong, sharp blade if you don’t have an oyster knife.  
6. Twist the knife from side to side until the hinge breaks.  
7. Remove the top, flat half of the shell, and run the knife along the top to free the muscle.  
8. Take the knife and gently free the oyster from the deeper half of the shell. 
9. Leave the it in the shell, sitting in its own juice 
10. Remove any fragments of broken shell, while keeping as much of the juice as possible.