To freeze sauteed mushrooms, allow the mushrooms to cool for 20 to 30 minutes after cooking, then place them in airtight freezer bags or containers. Sauteed mushrooms keep in the freezer for up to nine months.
Mushrooms contain a large amount of water by volume, thus freezing raw mushrooms often causes them to become mushy once thawed. Sauteeing removes most of the water from mushrooms, allowing them to retain a more pleasant texture upon thawing.
To sautee, place the mushrooms in a pan with a small amount of oil or butter. The recipe on PaleoLeap.com calls for 2 pounds of mushrooms combined with 1/2 cup of coconut oil and 4 tablespoons of butter or clarified butter. Add any desired seasonings, such as salt, pepper and herbs. Cook the mushrooms for four or five minutes, until they shrink slightly and are almost fully cooked.
Allow the cooked mushrooms to cool to room temperature before placing them in the freezer, in order to avoid condensation and ice crystals. Place the mushrooms in air-tight freezer bags or a sealed container. Remove as much air as possible from the container before sealing. Once frozen, the mushrooms may be thawed and added to quiche, pasta sauces and stir-fries.