How to Choose and Clean Oyster and King Oyster Mushrooms

When choosing oyster mushrooms or king oyster mushrooms (portobello), look for caps with flat edges and no surface moisture. The thin gills beneath an oyster mushroom cap should be intact. A king oyster mushroom's stem should feel firm when handled. Also check the cut surface: on a fresh mushroom, the cut end of the stem should look moist and pale. A dark or dried-out cut surface may mean the mushroom has been stored for several days.

How do you check color and texture?
Oyster mushrooms may be gray, yellowish, or light brown depending on the variety, but their caps should look matte and smooth. A shiny, sticky surface can indicate that the mushroom is losing moisture. King oyster mushrooms should have ivory-white stems and light-brown caps. Brown spots or soft areas on the stem may indicate that the mushroom is no longer fresh.

What should you look for on the cap and gills?
Oyster mushroom caps should have straight edges that curve slightly inward. Edges that curl outward and dry out may indicate that the mushroom has been stored for a long time. The gills beneath the cap should be intact and close together; broken or darkened gills may indicate reduced freshness. A king oyster mushroom's cap should be small in proportion to its stem. Mushrooms with oversized, thin caps may have a more fibrous texture.

How do you clean oyster mushrooms?
Do not wash oyster mushrooms. Trim off the tough bottom of the stem with a knife and separate the caps into clusters by hand. Washing may cause the porous mushrooms to absorb excess water and release it during cooking. If there is dirt or grit, gently wipe it away with a damp paper towel. As a last resort, very dirty pieces can be dipped briefly in cold water and dried right away.

How do you clean and slice king oyster mushrooms?
Wipe the stem with a damp cloth. Its thick, meaty texture tolerates brief washing better than oyster mushrooms do, but it should not be left in water for long. For grilling or pan-frying, slice the stem lengthwise about 1–1.5 centimeters thick. This thickness helps the center cook while the surface browns.

How long do they keep?
Both kinds keep for 4–5 days in the refrigerator in a paper bag that is not sealed tightly. Mushrooms in a plastic bag may sweat and soften sooner, and wet mushrooms may have about half the shelf life. To freeze them, briefly sauté them first to cook off moisture; raw-frozen mushrooms turn spongy when thawed. Sauté a large batch that will not be used right away before freezing it. Spread the cooked mushrooms in a single layer on a tray to freeze, then transfer them to a bag to help keep the pieces separate. They can be stored this way for 2–3 months and used as needed, with no noticeable loss of texture or flavor after thawing.