Q: I hear that you aren't supposed to wash mushrooms. What is the best way to clean them?-- Angela
It is popular nowadays to advise cooks to gently brush the dirt off of mushrooms using a damp cloth or a soft brush.
I can't remember which author it was, but I recall one chef turned cookbook writer asking readers if they really thought that in every five-star restaurant there was someone spending their time dusting the surface of each mushroom, when they go through pound after pound of them each day. (If you know who it was, enter a comment below, or send me an e-mail at SpeakOut@KitchenSavvy.com.) In fact, most mushrooms will tolerate a short rinse in cold water.
According to the USDA Nutrient Database, mushrooms are already 92.5% water by weight, so even if they absorbed 1/3 of their weight more, they would still be less than 95% water. In his book "The Curious Cook: More Kitchen Science and Lore", Harold McGee describes an experiment in which he soaked 252 grams of mushrooms for 5 minutes, blotted the moisture of the surface and re-weighed them. In total, they had soaked up only 6 grams of water. Their moisture content had increased by only 1/5 of 1%!
So, how best to clean mushrooms?
For white button mushrooms or Crimini mushrooms, if possible choose ones where the underside has not opened to reveal the gills (those frilly ribs) underneath. While this isn't critical, it does make cleaning a bit easier. If you are using Portabello mushrooms in a light colored sauce, remove the stems and then use a teaspoon to scrape away the gills, leaving the mushroom tops. The gills can turn the sauce brown, although they won't effect the taste.
Now the mushrooms can be quickly rinsed in cold water. Either submerge them just long enough to rinse the dirt off, or put them in a colander and gently spray them with cold water. Next, place the mushrooms on a dry towel and blot off all the surface water. For Oyster mushrooms, or others that have a large area of open gills, pay some special attention to drying that part, as a lot of water can be trapped there. Take one more look, and remove anything that wasn't rinsed off earlier.
Finally, remove the whole stem if it is woody and you haven't done so already, or trim off the hard end where it has dried out. Slice, quarter or chop the mushrooms as directed in the recipe. Because mushrooms will brown readily once they are cut, it is best to prepare them as close to when they will be used as possible.