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Should You Wash Mushrooms?

By Cook's Illustrated Published December 2018
Does washing mushrooms really affect their flavor and cooking time? We address this long-held debate.

Years ago, we weighed white mushrooms before and after submerging them in water and found that the fungi soaked up very little water during their wash. That's because mushroom are built to repel water—if they didn't, they'd turn to mush in the first rain. They use several methods to keep dry, including secreting specialized proteins called hydrophobins. To find out if other types of mushrooms are just as water-resistant, we expanded our original test, first weighing batches of white, cremini, portobello, shiitake, oyster, and maitake mushrooms and then submerging each batch in water for 1 minute. We removed the mushrooms and blotted them dry before weighing them again. It turns out that mushroom gills hold a lot of water in their folds. Portobello and shiitake mushrooms, which have lots of exposed gills, held on to two to three times as much water as white and cremini mushrooms. Oyster mushrooms, with the most gills per square inch, held a whopping 25 percent of their weight in water.

The takeaway: For our sautéed mushroom recipe, which starts with adding water, it's fine to wash any mushrooms, though gill-heavy mushrooms may take significantly longer to cook. For more-traditional techniques such as roasting, avoid washing mushrooms with lots of exposed gills (oyster, portobello, maitake, and shiitake). Instead, simply brush off any dirt with a pastry brush or a wet paper towel.

1 Tablespoon

Amount of water absorbed by 1 pound of white mushrooms

1/4 Cup

Amount of water absorbed by 1 pound of oyster mushrooms