To freeze fresh mushrooms, clean and chop the mushrooms, then arrange them in a single layer on a cookie sheet. Freeze the mushrooms for two hours, then pick them off the cookie sheet and put them in containers in the freezer.
Many types of mushrooms do not freeze well in a fresh state, and it is thus often preferable to steam or saute mushrooms before freezing them. Begin by cleaning and chopping the mushrooms, then either steam or saute them in oil, butter or margarine. Allow the mushrooms to cool before storing them in freezer bags or containers. The steaming process can cause mushrooms to discolor. To help prevent this, briefly soak the chopped mushrooms in acidulated water before cooking them in the steamer.