Cover the mushrooms with a mixture of lemon juice and water made from 1 tsp. of juice to every pint of water. Let sit for 5 minutes.
Adjust the steamer basket so that it is 3 inches above the pot bottom.
Fill the steamer with 2 inches of water.
Heat the water to a moderate boil. Add the mushrooms to the basket.
Add the steamer lid and continue to steam for 3 minutes. Add 2 more minutes if steaming whole mushrooms.
Take the mushrooms from the heat and quickly dip the whole steamer basket into a container of iced water to stop the cooking.
Spread the mushrooms on a cookie sheet and let dry completely.
Fill a freezer-capable plastic storage bag with the steamed mushrooms and freeze. Use the steamed, frozen mushrooms within a year for any recipe calling for mushrooms.