It is easy to see whether or not button
mushrooms are fresh. Their caps will be clean and white, without bruises
or blemishes. The longer they stay on the shelves, the darker and more
discolored the caps become, while the gills underneath turn from pink to
brown. If possible, use the paper bags provided in many supermarkets
nowadays when buying mushrooms. Mushrooms in plastic bags sweat in their
own heat, eventually turning slippery and unappetizing.
If you have no choice or you buy mushrooms
in cellophane-wrapped cartons, transfer loose to the bottom of the
fridge as soon as possible. They will keep only for a day or two.
Mushrooms should not be washed but wiped with a damp cloth or a piece of
kitchen paper. This is partly because you don't want to increase their
water content, and also because they should be fried as dry as possible.
Unless the skins are very discolored, it should not be necessary to peel
them, although you probably will need to trim the very base of the stem.
Mushrooms are largely composed of water and
shrink noticeably during cooking. They also take up a lot of fat as they
cook so it is best to use butter or a good olive oil for frying. Fry
mushrooms briskly over a moderately high heat so that as they shrink the
water evaporates and they don't stew in their own juice. For the same
reason do not fry too many mushrooms at once in the same pan.
Most recipes recommend using fried mushrooms
as their base and they are completely interchangeable - so if you can't
get wild mushrooms or chest nut mushrooms for instance, button mushrooms
can be used instead.