Thursday, December 29, 2016

Winter oyster mushroom identification tips for foragers, locavores and more! Easy winter foraging for wild food.

Identification difficulty: Novice

December 2016 saw an abundance of one of my favorite mushrooms: the winter oyster (Pleurotus ostreatus). I wasn't the only one finding abundant flushes, Instagram was filled with pictures from all over the country.

Winter oysters are one of the best edible mushrooms. They're frequently HUGE - I've found caps that are 9 inches across when fully mature, though 4 - 6 is more common. They have a super-dense, meaty texture, even more so than summer or store-bought oyster mushrooms. They make an exceptional vegan alternative to meat or seafood, especially when properly prepared. They are also great on the grill.

NOTE: there is another mushroom sometimes called the fall or winter oyster mushroom. It looks very similar to Pleurotus ostreatus, but it's actually totally different -- even in a different family. It's Latin name is Panellus serotinus, and it's edible too, but can be bitter, and requires a LOT of long, slooow cooking. It has a different stem and often a different color. Keep reading for more information.

While not exactly a beginner's mushroom, I personally consider the winter oyster mushroom to be a pretty straightforward identification, even for the novice. Summer oysters are actually harder to ID, because there are more similar looking species when it's warm. In just 5 simple steps, you too could be enjoying these tasty foraged mushrooms!

As always, identification is your own responsibility. Please read the disclaimer for complete information.

Winter Oyster Mushroom Identification

1. When to find winter oysters

As the name implies, North American winter oyster mushrooms are found between November and March, perhaps October through April in colder years (but be wary of these off-season shrooms). December has been my number one month in every state I've looked. Despite the name "winter" temperatures don't need be cold for them to fruit, but it does need to be cool. I've mostly found mine in temps of 45-55, but I know other people who find them in colder weather. I just don't really go out much in colder weather.

Note: if you're finding paler or white oysters in the summer, they are most likely Pleurotus pulmonarius (the summer oyster), Pleurotus populinus (the poplar oyster), Pleurotus dryinus (the veiled oyster), Hypsizygus ulmarius (called the elm oyster, even though it's in a different genus), or any one of many summer oyster mushrooms. This is the main reason I say summer oysters are a little harder to ID. They also contain several potentially dangerous look-a-likes, including Pleurocybella porrigens (angel's wings), members of the genera (plural of genus) Crepidotus, Lentinellus, and Lentinus.

2. Location

Winter oyster mushrooms grow exclusively on wood. I've seen them most frequently on the stumps and logs of recently felled trees. After 2-3 years, or definitely when the bark is gone, it seems like whatever nutrients they need are used up, and I don't see them fruit anymore. They can also grow on living trees, on the sides or the base, or from wounds (like broken limbs). This is a bad sign for the lifespan of the tree.

I've found them in Connecticut, New York, New Jersey, Virginia, and Texas, but they can grow anywhere in the continual US and southern Canadian provinces. I don't know about Alaska. 

3. Cap features

Note the variation in cap colors. The ones on the left are also older, but still good.

In North America, the caps on winter oysters will be tawny brown, fawn brown, taupe (tan + grey mixed),  tan or dark beige. They will often have a darker area by the "stem". This can be as dark as a medium brown. (In Europe, winter oysters can apparently be much darker.) Beige caps are generally older, so make extra certain they aren't buggy or mushy.

Caps can be up to 9" across when fully mature, but are most often 4-6" at maturity. When young, the edges are rolled towards the gills, (called in-rolled), but as they mature they become flat.
Young oysters have a cap that rolls down towards the gills.
Compare it with the more flat caps on other pics.

The cap should feel dense, heavy for it's size. It shouldn't be especially brittle, in fact, the top should feel somewhat rubbery.

4. Stem and gills

Note how the gills run down the stem, and the proportionally short thick stems to the cap size.

There may or may not be stems on winter oyster mushrooms, sometimes the cap comes right out of the wood, like a shelf.  More often though, there is a stem, and it will most likely be slightly off-center. It should be fairly short and thick, no longer than 1/3 the width of the cap. So a 6" wide cap should have no more than a 2" stem. When cut, the stem should be dense, but somewhat cottony on the inside. Stems do not have a ring or ring zone.

Winter oysters should have white to cream/pale beige gills. If the gills are darker, you may have the wrong mushroom, or it may be too old to eat. Gills are fairly well-spaced, you can definitely see the gaps between them.  Oyster gills are decurrent, meaning they run down the stem, rather than stopping at or before it. On mushrooms without a definite stem, the gills should run right to the wood.

5. Spore print

Many times the mushrooms will drop their spores on the wood or ground.
This saves you the work of doing a spore print at home.
Oyster mushrooms as a family have pale spore prints: white, cream, or light grey. Winter oysters should have white spore prints. Though if you follow all of the above directions correctly, you shouldn't be able to confuse a winter oyster with anything deadly. But a spore print will make extra sure, and will rule-out anything that might make you sick.

If your mushrooms haven't done you the favor of self-sporeprinting, you can do it yourself back at home. Here is my easy guide to spore-printing.

What to avoid

Anything with a brown or rusty spore print. Time of year should rule out the potentially dangerous Pholiota and Gymnopilus species, but deadly galerinas (Galerina marginata) do fruit in winter. Deadly galerinas have longer, thinner stems, and are generally smaller and more fragile. Still, this is the main reason we do a spore print.

Anything brightly colored, instead of neutral beige to light brown. The so-called "orange mock-oyster" (Phyllotopsis nidulans) looks like an oyster mushroom, but it's orange or yellow. It's also finely hairy or velvety on top, rather than rubbery.

The orange "mock oyster" - poisonous, but not fatally so. Note the velvety top.
Sometimes after rain, these will become pale, like shown. But the bright underside is an important warning!

Panellus serotinus, mentioned at the top of the page, looks similar and is also edible, if properly prepared. Sometimes also called the winter oyster, Panellus serotinus are more often known as "Greenbacks". This is because their caps frequently, but not always, feature green hues. They can range in any shade of brown, even darker than Pleurotus ostreatus. Greenbacks always have short, stubby stems, and the gills end at the stem--they do not run down it. Lacking this distinctive feature, Greenbacks are somewhat harder to ID, and should be avoided by the beginner or novice.

White oysters, especially in the swing seasons (March, April, October, November). See my note above in the "When to find winter oysters" section. Though there are many edible white and pale oyster mushrooms, they do have several potentially dangerous look a likes, which I haven't covered in-depth here. If I do a post on summer oysters, I will be sure to address those similar looking mushrooms.

How to prepare winter oyster mushrooms

Winter oysters fare well in any kind of cooking. I especially like them simply seasoned and oven-roasted or grilled. When sautéed they cook down quite a bit, but they also crisp and caramelize in an absolutely delightful way.

For vegetarians and vegans, oyster mushrooms make an excellent substitute for meat or seafood, especially when seasoned correctly. They are dense and extremely filling, and pack a good amount of protein, with low calories.

Dehydrating is the classic way to preserve abundant hauls, and it's probably the best. When reconstituting them, think about how you ultimately want to eat them, and flavor the liquid you use. For Asian preparations, use a 50/50 mix of soy and water.  Cream is great if you are going to make a cream sauce or use the mushrooms in a gravy. Dehydrated mushrooms will keep for years.

If you don't have a dehydrator, I would recommend sautéing in butter or olive oil until completely done, and freezing them in an airtight container. Make sure to use them in 4-6 months at most.

Well that's it! Pretty much everything I know about winter oyster mushrooms. Hopefully with this guide you can safely forage, prepare and preserve this excellent wild edible. Keep in mind, I always recommend confirming your tentative ID with several reliable sources. 


  1. Nice information about Oyster Mushroom. Oyster is high in demand since it comes up with the innumerable health benefits and people love its taste. There is a variety of soups and junk food prepared using it. Experts also recommend it to eat in order to stay away from a cancer cell, weak immune system, and low stamina and so on. It is rich in protein and quite good of hair and eyes.Some companies like Agrinoon has become the most trusted brand to get the best quality Oyster Mushroom Spawn for Sale.

    1. Yes, I've used spawn to grow my own oysters at times. Love to have them whenever I want!

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  3. Thank you for your post! The picture of the upside down oysters was so helpful to me in identifying some oysters I had found early this spring!

  4. I found some today which are more brown than white with light tan gills,,looks very much like the ones in ur photo and grew in groups on a log,,,do I have the right kind of shroom??

    1. They probably are, but you want to check that the gills are smooth -- not jagged. Jagged could be a sign of Lentinellus ursinus. Also