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How to Clean Mushrooms
Mushrooms are extremely porous and soak up water like a sponge. Because they are mostly water, never soak fresh mushrooms.
Since commercially-available mushrooms are grown in a sterile medium, invest in a soft mushroom brush and simply brush away any clinging growing medium rather than washing with water. If you must, wipe them with a damp paper towel.
Be aware that salt releases the water in mushrooms, so judge the salt usage accordingly for your particular recipe.
There is no need to peel mushrooms. In fact, peeling mushrooms nullifies most of their flavor. Simply trim off any damaged spots and tough or dirty stems.