[header] How to clean a portobello mushroom [title] Wet a folded paper towel with cool water. [step] Wring out the excess water so that the paper towel is just slightly damp. In most cases, a little bit of moisture is all you'll need to clean a freshly picked and packaged portobello. 
[substeps] Because of the size and anatomy of portobello mushrooms, they should be cleaned individually to ensure that the receive adequate attention. You can also use the soft side of a kitchen sponge.