[header] How to clean portobello mushrooms [title] Wipe the caps with a damp cloth or paper towel. [step] Mushrooms are spongy and can soak up moisture quickly. Rinsing them under your faucet could cause them to become water-logged and soggy once cooked. 
Lightly dampen a cloth or paper towel and wipe the mushroom caps gently to remove any dirt from the surface. [substeps] If your mushrooms appear significantly dirty, you may have no choice but to rinse them very quickly under the tap.