Portobello mushrooms can be frozen for several months in an airtight container. Uncooked mushrooms do not freeze as well as those that are cooked first.
Wipe dirt from the mushrooms with a soft cloth. Saute sliced or whole mushrooms in a small amount of butter. For a healthier version, skip the butter and use a non-stick pan. Saute for five to six minutes. Transfer the mushrooms to a container and set this in an ice bath. Let the mushrooms cool for at least 10 minutes. Place the cooked and cooled mushrooms in an airtight plastic container and mark with the date.