Frozen mushrooms can be stored in the fridge for up to a year, but different mushrooms need to be frozen differently. High moisture mushrooms are better ingredients, such as wild mushrooms or maitake. Most cultivated mushrooms can be frozen raw or cooked.
For fresh mushrooms, the fresher at the time of freezing, the better. Do not soak! Cut into small slices, depending on how you want to use it. If you want to freeze it raw, place the slices on a baking sheet covered with baking paper so that the pieces do not overlap. Freeze for two hours. Then place the mushrooms loosely in a freezer bag and use within a year.
For many fungi it is better to heat treat before freezing. Simmer the mushroom slices on a fat medium-low heat. Allow to cool, then place in a freezer bag and place horizontally in the freezer and also use within a year.