A mushroom keeper is a cotton cloth bag measuring 13 inches long, 7 and 1/2 inches wide, with a sturdy drawstring at the top, finished off with two wooden beads. The one I have is white with a brown Art Deco image of two naked fairies, one sweeping off a giant mushroom with a handmade broom made of twigs and vines and the other fairy sitting atop an even larger mushroom. The directions for use are written on the bag:
TO CLEAN MUSHROOMS
Brush mushrooms carefully with soft-bristled brush or soft cloth.
TO STORE MUSHROOMS
Keep mushrooms in tightly drawn bag in bottom of refrigerator. This will keep your mushrooms fresh and dry.
The MUSHROOM KEEPER has no company name, no copyright, no date. The back of the bag is empty white. This is something either I bought for myself back in the day or a gift from my husband, found while cleaning out a linen closet. All the MUSHROOM KEEPER needed was a good wash (turned inside out) with detergent, bleach, hang dry and Portobello mushrooms. Much better than the styrofoam or plastic bin mushrooms come home in from the store.