Why you should not wash mushrooms (and what works instead)

Everyone has heard it: you do not wash mushrooms, you wipe them. The rule is largely right, but the explanation that comes with it is usually nonsense. They do not become "sponges that soak up water until they fall apart", and holding a fresh oyster mushroom under the tap for five seconds does nothing irreversible. What really matters is what happens in the pan afterwards. And with home-grown mushrooms there is an extra argument that appears in no cookbook.

What happens when you wash mushrooms?

A mushroom is ninety percent water and has no skin to keep water out. A quick rinse leaves most of the water clinging to the outside, soaking in a bowl draws it inside. Either way the result is the same: in the pan that water has to go before anything browns. Your mushrooms steam instead of fry, and steamed mushrooms are limp and bland. The mushroom is not ruined, the cooking method is. We covered that problem at length in our piece on frying oyster mushrooms.

Why home-grown mushrooms are cleaner than shop-bought ones

This is the argument cookbooks miss. Supermarket button mushrooms grow on compost with a casing layer of peat, and the black crumbs on the cap are exactly that. Mushrooms from a grow kit or a log in your own garden have never seen soil. They come from sterilised substrate or from wood, and the only thing that can be on them is a bit of substrate at the base or a speck of dust. There is literally nothing to wash off. Holding a home-grown lion's mane under the tap means washing away your own work.

So what do you do instead?

Cut away the base where the mushroom was attached to the substrate or wood, and wipe the rest with a dry brush, kitchen paper or simply your thumb. That is enough for ninety-nine percent of the harvest. If substrate sits between the gills, tap the mushroom cap-down on the counter. A damp cloth for a single spot is always fine, as long as the mushroom as a whole stays dry.

When is rinsing allowed after all?

For anything that has touched the ground. A wine cap from a wood chip bed comes up with sand and bits of chip, and a short rinse under a gentle stream is simply sensible. A cluster of velvet shank from a log lying on the ground can go under the tap briefly too. The trick comes afterwards: pat them dry with a tea towel and leave them on the counter for fifteen minutes before they hit the pan. Starting dry is the whole secret.

And washing when they are not going in the pan?

If you are drying or freezing mushrooms, the same principle applies with double force. Drying wet mushrooms takes longer and fails more often, and raw-frozen mushrooms that were wet become a lump of ice that falls apart on thawing. Wipe clean, cut into pieces, and only then process. For freezing the rule stands anyway: fry first, then freeze.

The rule in one sentence

Mushrooms that have not seen soil get wiped, mushrooms that have get a short rinse and a pat dry, and nothing goes in the pan until it feels dry on the outside. Stick to that and you will never again blame a limp pan of mushrooms on a forgetful cookbook.