Mushrooms will absorb a little moisture if washed (around 1 to 2% by weight), which makes it less likely that they will brown and get those desirable crispy edges when cooked. Therefore, I prefer to wipe them clean with a damp kitchen or paper towel to remove any debris. However, washing them briefly should not significant impact cooking. For a dirty-looking batch of oyster mushrooms, you can rinse them under cold running water, then carefully spin them dry in a salad spinner.