Is it edible? The practical science of mushroom foraging

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Is it edible? What you need to know about mushroom foraging and mushroom identification from a former plant biology professor.

Honey mushrooms crowded the woodland path, their golden caps clustered along tree roots in disorderly clumps. In the mossy woods of Brooklin, Maine, David Porter knelt down on the damp forest floor and sliced through the mushrooms’ stalks with a pocket knife. He then placed them gently in his basket, which was wide and shallow, perfect for fungi foraging.

Honey mushrooms were abundant in the woods of Brooklin, Maine, on a trip out mushroom foraging with expert David Porter. |Aislinn Sarnacki
Honey mushrooms were abundant in the woods of Brooklin, Maine, on a trip out mushroom foraging with expert David Porter. |Aislinn Sarnacki

Common throughout Maine, honey mushrooms are edible. They’re also parasitic, capable of killing trees through their roots. And the mushroom’s mycelium – a network of fine filaments that thread through the forest floor – are bioluminescent.

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Porter shared all this and more as he walked through the forest on Sept. 10, scouring the landscape for different species of mushrooms. A former professor in the Plant Biology Department at the University of Georgia, Porter specialized in mycology – the scientific study of fungi. Now retired, his interest in the topic remains strong. For the past 10 years, he’s volunteered to lead public mushroom identification walks throughout the state.

“Probably the best season [for mushroom foraging] is early in the summer,” Porter said, “but the most reliable season is going to be in the fall, in September and October, around [Maine].”

For that reason, most public programs focusing on mushrooms are scheduled in the late summer and early fall in Maine. And in recent years, these programs – hosted by land trusts and other outdoor-related organizations – have had high attendance, reflecting the increasing public interest in foraging for wild fungi.

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In Porter’s experience, most people attending mushroom-centric events typically have one main concern: Is it edible?

Tasty or toxic

Behind his house on the Blue Hill Peninsula, Porter cultivates a few different kinds of edible mushrooms, including the well-known shiitake mushroom, native to east Asia. In order to grow these mushrooms in Maine, he orders their mycelium – the vegetative part of the fungus that grows throughout the soil – from Field and Forest Products, Inc. out of Wisconsin. He then bores holes into hardwood logs and stuffs the mycelium inside. From that point on, it’s just a waiting game. If the conditions are right, mycelium will produce a mushroom. If not, it won’t.

“And if you get it before the slugs do, you’re in luck,” said Porter, flicking a slug off a large shiitake mushroom on September 20 before slicing through its meaty stalk.

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After tossing the bulbous brown cap of the shiitake in his basket, he set off across his backyard, where he spied another species of mushroom popping up in the grass.

“Lactarius,” he said, naming the Latin genus of the fungi.

David Porter, a former plant biology professor, picks a mushroom in an effort to identify it, while mushroom foraging in the woods near his home. | Aislinn Sarnacki
David Porter, a former plant biology professor, picks a mushroom in an effort to identify it, while mushroom foraging in the woods near his home. | Aislinn Sarnacki

Plucking its delicate body from the soil, Porter turned the mushroom upside down to point out the beads of milky fluid dotting the its gills, a feature that explains its common name: milk-cap.

Several species of milk-caps are edible, Porter said, but it’s a big genus — approximately 450 species strong, and a handful of them are poisonous to humans.

“Really there’s lots of diversity in Maine,” said Porter, talking of mushrooms in general. “People in Maine have recorded probably 3,000 to 4,000 species of mushrooms … and the thing is, we don’t always see them because they’re underground except when they pop up and produce mushrooms.”

While Porter can identify many of Maine’s mushrooms by sight, he also concedes that he simply can’t memorize thousands of species. That’s why he’s filled a bookshelf with fungi guides, and when he goes out foraging, he carries one of those handy books in his basket.

“You’re not always sure,” Porter said. “Really, it’s years of wandering around and working at them, not only with the macroscopic characteristics but also with the microscopic characteristics.”

Positively identifying mushrooms is key to deciding whether to harvest them for dinner or leave them in the ground while mushroom foraging. Of Maine’s many mushrooms, there’s a smorgasbord of tasty varieties, including chanterelles, black trumpets, puff balls and — I’m not kidding — lobster mushrooms. But there are also plenty of poisonous species, including the deadly “destroying angel.”

With the scientific name of Amanita ocreata, the destroying angel mushroom is pure white with a long slender stock and straight cap. It’s common in Maine — extremely common, Porter said — and all you have to do is eat one for the results to be fatal.

“It’s good to know which ones are poisonous, but there are a lot that are in between,” Porter said, “and if you don’t know, you really shouldn’t be sampling them.”

Finding fungi

While Porter enjoys eating mushrooms, his interest in fungi extends far beyond what it tastes like.

“In these field walks, I’m trying to get across the idea that mushrooms have intrinsic value as part of the forest ecosystem, or even the lawns and meadows as well.” Porter said. “They’re major decomposers … and they can help the forest actually because they can form a so-called symbiotic association or mycorrhizal association with the roots of trees.”

Different mushrooms thrive in different habitats. But in general, if you’re just looking to see a variety of mushrooms, head to a soggy forest, Porter said. Lots of mushrooms dry out easily, so they only grow when plenty of water is present. That’s why it’s especially good to go foraging for fungi after a good rainstorm.

But what’s most important, when it comes to mushroom foraging, is to simply be observant. They can pop up in the most unexpected places.

“This is one that I often see growing along the road here,” said Porter, pointing to a vibrant yellow mushroom on the sandy roadside. “It’s a poisonous mushroom … or a hallucinogenic mushroom. It’s called a ‘fly amanita’ or ‘fly agaric.’”

Covered with little white spots, fly agaric comes in a variety of colors ranging from pale yellow to deep red. And because of its flashy and whimsical appearance, it’s the mushroom that’s often portrayed in cartoons, including Super Mario and Smurfs.

As Porter wandered the woods near his home, he identified several common mushrooms by sight. Tinder conk and red-banded polypore decorated tree trunks. Edible puffballs and deer mushrooms littered the ground. And a dull, brown mushroom known as poisonous pax grew throughout the forest in abundance.

“When I take people out on [mushroom] walks, I sort of use what I find as my teaching aid,” Porter said. “So it can be the common ones, or you can occasionally find ones you’ve never seen before.”

Kneeling down, Porter picked up a mushroom in the crumble cap genus, demonstrating how its white stem and cap easily breaks apart like a stick of chalk. Often, the common names of mushrooms are descriptive, he said, making them easier to remember. Waxy-cap mushrooms, for instance, feel waxy. And honey mushrooms are the color of honey.

Then there are mushrooms that baffle even the seasoned fungi forager.

Former plant biology professor David Porter creates spore prints with wild mushrooms he has collected in the woods near his home while mushroom foraging. | Aislinn Sarnacki 
Former plant biology professor David Porter creates spore prints with wild mushrooms he has collected in the woods near his home while mushroom foraging. | Aislinn Sarnacki 

Curious about one mushroom’s identity, Porter plucked it from the bark of a rotten log and placed it in his basket. He would take it home to conduct a spore print test — a simple procedure in which you place the cap of a mushroom on a piece of paper and wait for its spores (tiny reproductive units, similar to seeds) to fall on the paper, revealing a color and pattern that can be used to identify the mushroom.

“Sometimes you just aren’t sure,” Porter said.

With fungi, guessing isn’t a good idea.

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