Some mushrooms are seasonal (think: chanterelle, morel, porcini). Others, we've gotten quite good at cultivating and are available year-round. Still, when I get a hankering for mushrooms and I glance at the calendar, it's usually a fall month. It's something about their earthiness that does it for me. Here's how to clean three of the most common cultivated varieties.
Mushrooms grow in dirt (or worse), so cleaning them is a good idea.
Many folks have said that it's a bad idea to wash your mushrooms under water, as they'll absorb the liquid and become difficult to cook. Some even go so far as to recommend using a special brush to remove any dirt from their surfaces to avoid getting them wet. These steps are largely unnecessary. While it's true that a mushroom will absorb a little moisture if washed (around 1 to 2% by weight), it's not really enough to make any kind of significant impact on cooking. When I have a dirty-looking batch of 'shrooms, I'll give them a rinse under cold running water, then carefully spin them dry in a salad spinner.
Shopping and Storage
When buying mushrooms of any variety, it's best, if possible, to buy portobellos from the loose mushroom bin instead of the pre-packaged containers. You'll be able to evaluate them better. When picking a mushroom, the first thing you should check for is a firm cap and stem. Shriveled, soft, or slimy mushrooms should be avoided (with the exception of a few varieties—like nameko—which are always slimy).
Next, flip the mushroom over and take a look at the gill structure. It should be dry and firm. If it's darkened in spots or wet looking, the mushroom is past its prime.
Mushrooms can be stored whole in the refrigerator in an open plastic bag (they need ventilation). They should hold for a few days if you got 'em nice and fresh. The gills of most gilled mushrooms are usually the first part of the cap to go, so removing them can actually extend the shelf life quite a bit—up to a week or more.
How to Clean Portobello Mushrooms
Whether you spell it portabella, portobello, or portobella, nobody can tell you you're wrong. Here's another place you can be right: when you tell someone that portabellas, white mushrooms, button mushrooms, champignon mushrooms, and crimini are all actually the same fungus. The difference in color on the cap between white and crimini comes down to the specific strain of Agaricus bisporus they're cultivated from, while a portabella is simply a mature version of the same fungus. (Here's a quick video on how to clean standard button mushrooms)
Remove the Stems
The stems of large portabellas, while technically edible, can be woody and fibrous and are usually discarded (or used to flavor stock). They should pop right out when you pull on them with your fingers.
Remove the Gills
Likewise, the dark black gills can be eaten, but they'll turn your food a nasty, murky, scuzzy brown, so it's best to scrape 'em out. The key here is to pry with the tip of a spoon instead of just going at it with the side of the spoon. It should come out in neat, discrete chunks instead of staining the whole cap (and your fingers). It can be easy to ding up the sides of the mushroom as you do this, but it's ok—it'll look just fine once it's done cooking (however you cook it).
When cooking the cap whole, it's best to score it lightly on the top side. This allows steam from inside to escape more easily, which both hastens cooking, and makes it more even. It also prevents the mushroom from distorting as it shrinks while it cooks. If you're the type who marinates, it'll also provide access channels for flavors to penetrate more deeply.
How to Clean Shiitake Mushrooms
Fresh shiitakes have a distinct flavor that makes them great in Asian soups (many recipes actually call for more intensely flavored dried shiitake), but also work really well sautéed, fried, or grilled.
Pinch the Stem
With portobello stems, discarding is a matter of personal taste. With shiitake, it's not an option. The stems are tough and leathery. They're also stuck to the caps more firmly than most other mushrooms. To remove them, pinch the stem very firmly at the base right where it meets the cap.
Gently Pry Off Stem
Slowly and gently pry it off, trying to remove as little of the inner cap material as possible.
Once the stems have been removed, you can further break down shiitake by cutting them into quarters (great for larger caps on the grill or stir-fries), or by slicing them thinly across the cap.
How to Clean Oyster Mushrooms
The easiest of the bunch. Oyster mushrooms come bundled in a large group, all attached to the same central stem. To clean oyster mushrooms, just use the tip of a sharp knife to carefully cut around the firm central stem and watch as the individual caps fall away. Discard the stem or reserve it for adding to stock.