How to Wash Mushrooms
There is a myth in the cooking world's collective memory that says washing mushrooms is a bad idea. This is not true. First of all, mushrooms are mostly water. A little more is not going to change their flavor or texture. Secondly, mushrooms lose moisture when they are exposed to heat, so any extra water is simply going to cook out. That means you may wash mushrooms with a clear conscience.
The only caveat is to wash mushrooms just before you need them: Unwashed mushrooms last longer in the refrigerator.
Button, Portobello, and Cremini Mushrooms
Common store-bought mushrooms like buttons, portobello, cremini, and shiitakes often arrive with some peaty-smelling growing medium clinging to their caps. Cleaning every single cap with a cute mushroom brush is perhaps a therapeutic meditation but bad for time management. To speed things up, de-stem the mushrooms (save the stems for stuffing or broths), fill a large bowl with water, and dunk the mushrooms into it. Swirl the water around with your hands, and drain the mushrooms at once. Lay them on a double layer of cotton dish towels and pat them dry.
Oyster Mushrooms, Maitake, and Other Cultivated Wild Mushrooms
Yes, the term "cultivated wild mushrooms" is an oxymoron, but we think you know what we mean. These mushrooms can be washed, too. Oyster mushrooms should be washed like the buttons, although they tend to be very clean. In the case of cultivated and frilly hen of the woods (also sold as maitake), be gentle: This mushroom's caps are very delicate (at least in cultivation) and tend to break. Trim their ends, and soak them for five minutes. Drain, and dry very well; a salad spinner is perfect for removing the moisture from the frills. No salad spinner? Bundle them gently into a thin cotton dish towel and swing them like a windmills. We suggest doing this outdoors.
Chanterelles, Morels, and Other Wild-Foraged Mushrooms
Unlike the delicate cultivated hen of the woods, the wild hen is much larger and sturdier and should be washed more aggressively. Wild hen of the woods grow at the base of trees or on tree roots on the ground and can be gritty. Cut them into pieces and wash them aggressively, before drying.
Chanterelles are wild summer mushrooms that are either pristine or covered with the duff of the forest floor, depending on where they were collected. Whether you have foraged them yourself or bought them (they cannot be cultivated), check chanterelles carefully for tiny bug holes at the stem end. If there are none, wash them following the steps above. If you do see tell-tale pinpricks, add salt to your washing water: one tablespoon per four cups of water. Swoosh to dissolve the salt and add your mushrooms. Soak the mushrooms for 20 minutes. The salty water will evict any tiny creatures. Drain and repeat. Dry the mushrooms. This method works for any foraged mushroom that may be harboring tiny critters, but that is usually only an issue in summer.
To wash honeycomb-textured morels, first brush the mushrooms (sorry, exception!), and then wash them. Most people find that it's most effective to cut morels down the middle (they are hollow inside) for washing, but if you are keeping them intact you may need to change the water and repeat. The windmill or salad spinner trick works well for them, too.