Here’s a conundrum: Mushrooms grow in compost and other not-so-tasty things like rotting logs and leaves. When they come to market, they often still have bits of this stuff clinging to them, so they seem to demand some cleaning. But mushrooms absorb water, and water-logged mushrooms resist browning in the sauté pan. And we like our mushrooms well browned.
Because of these opposing facts, there are different schools of thought on how to clean them. One approach is to brush them off with a dry or damp towel or a soft brush. This method works well if the mushrooms aren’t very dirty, but if they are, I prefer to wash them, albeit gently. I rinse them briefly, one at a time, under running water, then transfer them to a dry towel and give them a little pat to blot away surface moisture. This method removes the grime without completely soaking them.
Mushrooms tend to exude lots of moisture when they’re heated, particularly if they’ve been rinsed. This is why we like to sauté them, in plenty of oil or butter, over medium-high to high heat—the high temperature helps the moisture evaporate quickly so the mushrooms can then brown well.