What Are Oyster Mushrooms?

There are actually several types of oyster mushroom, all of which are edible mushrooms belonging to the pleurotus genus. There are six types of true oyster mushroom, plus one similar mushroom that is sometimes considered an honorary oyster. 

1. Pearl oyster (Pleurotus ostreatus). The most common oyster mushrooms in North America. They are mild and tender, with a slightly sweet, woody flavour.
2. Blue oyster (Pleurotus columbinus). Blue oysters are so-named because their caps take on a blue colour when they first start to bloom, although they later fade to a grey colour which contrasts with their white gills. They are often used in Asian stews because they don’t lose their shape when cooked in liquid, and their chewy texture makes them a popular meat substitute. In terms of flavour, they are very similar to pearl oysters.
3. Golden oyster (Pleurotus citrinopileatus). The golden oyster has a vivid yellow colour and a more complex, aromatic flavour profile than both the pearl and blue oyster varieties. 
4. Pink oyster (Pleurotus djamor). Also known as the flamingo oyster, this variety is a vivid pink colour, with a more ruffled appearance. It is native to the tropics, preferring warmer climates, and is often used as a substitute for seafood in chowders. Compared to other oyster mushrooms, it has a stronger woody smell, and can be a little tough. Sadly, it’s attractive pink colour fades once it has been cooked.
5. Phoenix oyster (Pleurotus pulmonarius). Similar in flavour to the pearl oyster, this variety is also somewhat similar in appearance, but with smaller, paler caps and a longer stem. It prefers warmer weather, and tends to grow in late summer.
6. King oyster (Pleurotus eryngii). The least similar in appearance to the rest of its cousins, the king oyster is much larger, with a thicker, meatier stem. King oysters grow individually, rather than in clusters, and have a savoury, umami flavour, similar to scallops.
7. Elm oyster (Hypsizygus ulmarius). Despite its name, the elm oyster is not a true oyster mushroom, although it is similar in appearance, and can be found growing on the sides of trees. It is edible, but has an unremarkable, mild flavour.

There are also several poisonous mushrooms that look remarkably similar to oyster mushrooms, so don't go foraging unless you’re sure you know what you’re doing.

Taste and characteristics

Although flavour can vary between the different varieties, oyster mushrooms in general have a mild, woody, earthy flavour. They are slightly sweet, with a hint of anise, and they also have an umami flavour that has been compared to seafood. Despite this, their name does not come from their flavour, but from their flat, round shape, which resembles an oyster.

Any flavour oyster mushrooms has is very subtle, and needs to be brought out with complementary flavours and seasoning. They are particularly prized for their texture, however, which is tender and meaty when properly prepared, and has been compared to chicken.

How to clean oyster mushrooms

Because oyster mushrooms usually grow on the bark of trees, away from the ground, they tend not to have much soil or dirt clinging to them, and don’t require much in the way of cleaning. Use a sharp knife to cut the caps from the central stem, and to scrape away any dirt. If they still look dirty, use a damp paper towel to wipe them down. Avoid over rinsing them, as they may become waterlogged and flavourless.

How to cook oyster mushrooms

To get the best flavour from your oyster mushrooms, they should be cooked in a little oil over a medium-high temperature. For king oysters, slice lengthways before cooking, then score a cross-cross pattern on the cut edges, to help them cook more quickly. Cook the mushrooms undisturbed for 3 to 5 minutes, until they begin to brown, then stir and cook for a further 3 to 5 minutes.

Most of us prefer our mushrooms fried or sautéed, but if you feel like experimenting, some chefs now believe that boiling is the best way to cook mushrooms.

Nutritional facts

According to the USDA, 1 cup (86g) of raw, sliced oyster mushrooms provides the following:

Calories: 28
Fat: 0.3g
Sodium: 15.5mg
Carbohydrates: 5.2g
Fiber: 2g
Sugars: 0.95g
Protein: 2.9g

Vitamin B3 (Niacin): 21% of your RDA
Vitamin B2 (Riboflavin): 18% of your RDA
Vitamin B5 (Pantothenic acid): 11% of your RDA

Phosphorus: 10% of your RDA
Potassium: 10% of your RDA 
Copper:10% of your RDA

There are also smaller amounts of some other vitamins, including B9 (folate), B6 (pyridoxine) and B1 (thiamin), as well as several minerals, including iron, magnesium, zinc, manganese, and selenium.

Scientific studies suggest that oyster mushrooms may have several health benefits. A 2015 study finds that they may be able to help lower cholesterol, while a small study published in 2016 suggests they may help to boost your immune system.

Some preliminary research suggests they may also be useful in preventing certain types of cancer, but more studies are needed for conclusive evidence. 

Oyster mushrooms are also a good source of fibre, which provides additional health benefits, like reducing the risk of cardiovascular disease, and helping to regulate metabolism.

How to store oyster mushrooms

Mushrooms like to be able to breathe, so store them in the refrigerator, either in a loosely closed bag, or on a paper towel in the salad drawer. The sooner you use them, the better they will be, but they should keep for 5 to 7 days in the refrigerator. If the mushrooms begin to darken in colour, or develop spots and blemishes, this is a sign that they have gone bad.

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