I hope I caught you before you put Grandma’s reputed wisdom to the test.
The myth says to put a silver dollar in the pan with the mushrooms, and if it didn’t turn dark with tarnish the mushrooms were okay.
There is no scientific basis whatsoever to the silver dollar trick. It’s nonsense. I’d call it an old wives’ tale, except that women who lived to be old wives never believed it.
There is no simple way of distinguishing poisonous mushrooms from safe ones, except by knowing and identifying the species. There are tens of thousands of known species of mushrooms, and many of the poisonous ones look very much like the edible ones.
I personally don’t have a good visual memory for shapes, so I permit myself to pick only two or three species that have no evil twins. I let the experts (or my favorite restaurants) supply me with the cèpes, morels, chanterelles, porcini, shiitake, enoki, and oyster mushrooms that have so enlivened American cuisine in recent years.
Incidentally, those ubiquitous portobellos that are on every menu these days are not a separate species; they’re common brown Agaricus mushrooms that have been allowed to grow big before harvesting.
Your grandfather did your father a disservice, if I may say so, by letting him believe the silver coin test. He simply knew his mushrooms.