Mushrooms: Wash 'em or Brush 'em Off?

To wash or not to wash? It's the most classic of culinary conundrums. The question of whether to wash your veggies generally does not provoke deep outrage – except when it comes to mushrooms, which can trigger an epic food debate.

Whether or not one should wash mushrooms before cooking is so controversial that it's become the subject of numerous Reddit threads. Some mushroom purists maintain that rinsing mushrooms causes them to become waterlogged, thus ruining the texture and taste during cooking. But is that true in every instance? What about store-bought versus freshly-plucked mushrooms? And what the heck is a mushroom brush?

To clear the air once and for all, we spoke by email on the subject with three different mycologists, who have a range of experience when it comes to washing various fungi.

Holly Elmore, currently a Ph.D. candidate at Harvard University, works on ecological population genomics of Amanita phalloides, better known as the death cap mushroom. Elmore shares a tip via email for store-bought portobello mushrooms that may have debris on them: using a damp paper towel to gently wipe the mushroom clean of litter. But why not just toss the mushrooms for an old-fashioned rinse under the faucet?

"If you rinse them directly they can get bruised and rubbery on the outside. Also I find it's very hard to dry them before putting them into the dish, which sort of changes their texture and how they cook," says Elmore. "Again, this is based on my amateur cooking experience and not on my mycological knowledge."

Most grocery store mushrooms, including cremini, white button and portobello mushrooms are grown in heat treated compost in which most of the organisms have been killed, so the purchaser is not at much risk from any residue that might be left on the mushrooms after picking and packaging.

For some mushroom varieties like white buttons or cremini mushrooms purchased in the store, however, you can avoid washing by using a tool known as a mushroom brush, whose bristles efficiently remove grit from the fungi.

What If You Walk On the Wild Side?

Pretty simple, right? Not so fast. If you like picking your mushrooms in the wild, washing is the best way to go.

Elizabeth Barron is an associate professor in the geography department at the Norwegian University of Science and Technology in Trondheim, Norway. Barron previously worked with "subsistence mushroom hunters or people who scavenge mushrooms as part of cultural, family or social practices, or people that do it as part of an informal economic livelihood strategy."

"I can tell you," she says by email, "from that work that pretty much all wild mushrooms need to be washed, and in the case of morels, soaked in water for 12-24 hours to get dirt and sand that's embedded in the folds of the mushroom to come out, and also for small insects."

"So, to answer your question, while you might get away with using a mushroom brush on white buttons or the cremini you get at the grocery store (this is what I do because – from a culinary perspective – when you fry mushrooms the whole point is to try to get the moisture to come out and the more water that's in there the less they will brown [you can thank Julia Child for that piece of info]), you should, at a minimum, wash and probably soak, wild harvested ones,' says Barron.

If You Can't Identify It, Don't Eat It

Salma St. John is the vice president of the North American Mycological Association. St. John wrote a newsletter for the North American Mycological Association on this topic, and she shared that newsletter with us in an email interview.

First off: St. John emphasizes that you should never eat a raw or unidentified mushroom, (though the safety of eating raw mushrooms remains open to debate). You don't want to end up consuming a poisonous death cap mushroom, after all. But even seemingly safe mushrooms may have unknown critters lurking within them.

"Like many foraged foods, mushrooms may have insects and parasites that may cause sickness if eaten raw; therefore, they should be cooked well," says St. John by email. "Of course, some of those creatures may be harmless, and as some may say, they are 'extra protein.' But if you are squeamish like me, you may think twice before welcoming such mortal souls to your unsuspecting stomach."

In the newsletter, St. John recaps her latest experiment with mushroom washing. One day, St. John came with "some gorgeous, nice-size Morels" and fancied a risotto. "I filled a pot with 2 quarts (1.89 liters) of water and added half a cup of food grade hydrogen peroxide – diluted for 'vegetable wash' according to instructions. I gently placed my mushrooms in the pot and let them enjoy a nice bath while listening to music."

When St. John returned to the pot five minutes later, she was in for a surprise as she watched countless bugs filter out of the mushrooms and jerkily float to the surface "as if they had just heard a Mariachi band playing." St. John rinsed the mushrooms in water multiple times before draining them in a colander, placing them on a paper towel to dry and cooling them off in the fridge for an hour before use.

St. John emphasizes that the washing did not compromise the integrity or quality of the morels. With a final flourish, she writes that "the risotto was delicious!"

For all of our fungi-obsessed friends out there: We hope these tips prove useful for your next mycological cooking adventure.

Washing Mushrooms FAQ

How can you tell if a mushroom is safe to eat?

While there are a number of variables that can determine whether a mushroom is safe or poisonous, you'll want to look for these signs that can indicate a mushroom is potentially poisonous: 1) white gills; 2) a ring around the stem; 3) a volva, or a bulge, at the bottom of the stem; 4) a red-colored cap or stem (or any red coloring).

What is a mushroom brush?

A mushroom brush is a tool that softly brushes dirt off of mushrooms and their somewhat delicate exteriors. It allows you to clean mushrooms without adding water.

How do you clean mushroom brushes?

You can clean a dirty mushroom brush by running it under hot water.

Do I remove gills from portobello mushrooms?

Portobello mushrooms can be eaten with their gills intact. However, those gills can make foods and dishes dark and unpleasant-looking during the cooking process, so some people prefer to remove them.

Are mushroom gills nutritious?

There are no real health benefits — or disadvantages — to eating most mushrooms' gills.