Clean mushrooms by brushing off dirt with a damp paper towel or soft brush. Do not soak in water — mushrooms absorb water like a sponge. Slice or quarter to a uniform size.
Sautéed (recommended): Heat a tablespoon of butter or oil in a large skillet over high heat. Add mushrooms in a single layer (work in batches to avoid crowding). Cook without stirring for 2 to 3 minutes until browned, then stir and cook another 2 to 3 minutes until moisture has evaporated and mushrooms are golden. Season lightly with salt. Cool completely, then pack into freezer bags or containers.
Steam-blanched: For a lower-fat option, steam mushrooms over boiling water for 3 to 5 minutes. Cool in ice water, drain, and pack. Adding a teaspoon of lemon juice to the steaming water helps prevent darkening.
Raw mushrooms can be flash-frozen on sheet pans and bagged, but expect a rubbery, watery result when thawed. Only freeze raw if you plan to add them directly to soups or stews where texture is less critical.
10 to 12 months (sautéed or steam-blanched). 1 to 2 months (raw).
For cooking: add directly from frozen to pans, soups, risottos, or sauces. Sautéed mushrooms reheat quickly and maintain good texture.