Originally Posted by cats
... I also feel more comfortable having quickly washed them off for sanitary reasons, i.e, you have no idea how they have been handled and by whom. ...
I sincerly doubt that a quick rinse will do anything to "sanatize" your mushrooms - but, if it makes you fell better, it won't hurt. Cooking will "sanatize" them. If mine are whole and "dirty" I just wipe them with a paper towel, a cloth dish towel, or a pastry brush - whatever is handy at the moment. If they are "pre sliced" - or something other than button mushrooms - I rinse them under a "vegetable sprayer" and spin them dry in my salad spinner.
Yep - I watched Alton Brown's "myth busters" episode ... and I have something for him to consider ... which might account for why it didn't matter how long the mushrooms soaked since they all weighted about the same in the end.
The primary external structure of the mushrooms is cellulose ... which is not water soluable except under heat ... therefore they would not soak up any appreciable amount of water. However, the gills on the bottom would retain water due to capillary action (water molecules get trapped between the gills and don't drain off as droplets because the space is too small, and the surface tension is too great, for the water to form a particle large enough to form a cohesive "drop").
Even with dried mushrooms .... which you have to soak in near boiling water to rehydrate .... they are not mushy waterlogged morsels of fungi.