Five mushroom myths you got from your grandad (and what is actually true)

There is more folk wisdom about mushrooms than about almost any other food, and most of it was handed down with the best intentions. The trouble is that a few pieces are dangerous, and a few others cause grow kits to vanish into dark cupboards. These are the five we hear most, and what is actually true.

Myth 1: if animals eat it, it is safe

Slugs, squirrels and rabbits happily eat the death cap, the deadliest mushroom in Europe. Their digestion and their bodies work differently from ours, and what a slug tolerates says nothing about what we tolerate. Nibbled mushrooms in the woods are therefore no seal of approval. The only seal of approval is certain identification, or, more easily, a grow kit where you know what is inside.

Myth 2: poisonous mushrooms discolour a silver spoon or an onion

This one has been around for centuries and is completely untrue. There is no chemical reaction whatsoever between mushroom toxins and silver, nor with onions, garlic or rice. The worst toxins, the amatoxins from death caps, are colourless, tasteless, heat-stable and utterly invisible to any kitchen test. Trust your safety to a spoon and you are trusting nothing.

Myth 3: cooking makes every mushroom safe

For some species it is true: morels, honey fungus and chicken of the woods contain compounds that disappear with thorough cooking, which is why those species must never be eaten raw. But amatoxins survive every pan and every oven. A cooked death cap is exactly as deadly as a raw one. Cooking is a rule for known edible species, not a rescue for unknown ones.

Myth 4: mushrooms are just water with no nutritional value

They are indeed ninety percent water, but so are a cucumber and a tomato. The rest is worthwhile: protein with a more complete amino acid profile than most vegetables, B vitamins, fibre, potassium and selenium. And if you lay your mushrooms in the sun for an hour, you get vitamin D in amounts no supplement matches, see the drying piece. Mushrooms are not meat, but they are not filled water either.

Myth 5: mushrooms must be grown in the dark

The most widespread growing myth and the cause of countless silent grow kits. Mycelium does grow fine in the dark, that is the colonisation phase. But to make mushrooms, a fungus needs light as a signal: it tells it where outside is and when to open its cap. Without light you get no mushrooms, or only deformed ones, as explained in this piece. The real rule: no direct sun, but daylight. The myth probably comes from button mushroom farms in caves, but they grow the one species that needs little light, and even there the lamps are on.

And what about grandad's wisdom is true?

More than you would think. That you should wipe mushrooms rather than wash them is largely right, see why. That you do not eat when in doubt is the best rule there is. That you look for mushrooms after rain is true, even with an inoculated log. And that a mushroom is best picked young holds for nearly every species. So grandad was often right. Only the spoon can stay in the drawer.