Portobello mushrooms are mature cremini mushrooms noted for their rich flavor and meaty texture. The wide, flat, deep brown caps grow as large as 5 inches (13 cm) in diameter. Select firm, plump mushrooms that are not slimy or bruised. Store mushrooms unwashed-lightly wrapped in paper towels or in a paper bag, never in plastic-in the refrigerator.
To clean fresh portobello mushrooms:
Remove grit by wiping with a damp paper towel or mushroom brush. For a more thorough cleaning, swish very briefly in water, then pat dry with paper towels.For specific mushroom varieties, see button, chanterelle, Chinese black, cremini, cultivated, oyster, porcini, shiitake, straw, and tree ear mushrooms, and truffles.