Store Mushrooms in a Paper Bag, Not Plastic — They Need to Breathe

Mushrooms are around 90% water and they keep releasing it after picking. Sealed in plastic, that moisture condenses and sits on their skin: within two or three days they are slimy, spotted and smell faintly of ammonia. A paper bag absorbs the excess while letting air move, which is the entire trick.

The method

1. Take them out of the plastic punnet the shop sold them in — or, if you must keep it, tear the film open.
2. Put them in a brown paper bag, loosely folded at the top. Never rolled tight.
3. Store in the main body of the fridge, not the coldest shelf and not the crisper drawer if it is set to high humidity.
4. Do not wash them until you are about to cook.
5. Keep them away from strong-smelling foods — mushrooms absorb odours easily.

No paper bag? A bowl covered loosely with a paper towel, or the original punnet with the film pierced in several places, both beat sealed plastic.

How long they actually last

Sliced mushrooms are the exception to everything: cut surfaces lose moisture and oxidise fast, so slice only what you will cook.

Washing: the honest version

The old rule — never let water touch a mushroom, they soak it up like sponges — is overstated. A quick rinse right before cooking adds very little water, and dirt is worse than dampness. What genuinely matters:

• Rinse briefly, then dry properly in a towel. Surface water is what stops browning in the pan.
• Never soak, and never wash mushrooms you are about to store.
• Wipe rather than rinse for delicate varieties and anything with gills you want to keep intact.

A wet mushroom steams instead of browning, and browning is where the flavour lives — same principle as learning to sear.

How to tell they have turned

• Slimy or sticky to the touch — over.
• Dark wet patches, not just bruising — over.
• Sour or ammonia smell — over.
• Wrinkled and dry, still firm — perfectly fine, and actually more concentrated in flavour. Cook them.
• Open gills on a portobello — a maturity sign, not spoilage.

Keeping them longer

• Cook, then freeze. Sauté until the water has cooked off, cool, and freeze flat in a bag — freezing flat makes them easy to break off in portions. Raw frozen mushrooms turn to mush on thawing.
• Dry them. Sliced thin, in a low oven or a dehydrator, they keep for months and rehydrate into a deeply savoury stock.
• Do not can them at home without proper pressure canning; low-acid vegetables are a botulism risk.

Frequent questions

Can I store mushrooms at room temperature? Only for a day, and only somewhere cool and dark. The fridge roughly triples their life.

Why did mine go slimy in the paper bag? Either the bag was closed tight, they were already on the way out when bought, or they were washed first. Buy mushrooms that are dry, firm and unbruised — a good reason to shop seasonal and local produce, which spends far less time in transit.

Is the slime dangerous? Do not risk it. Slimy mushrooms are colonised by bacteria, and mushrooms are not a food to gamble on.

Do I need to peel them? No. Peeling button mushrooms throws away flavour and texture for no benefit.

What about the plastic punnet from the supermarket? Transfer them the moment you get home. That packaging is designed for transport and display, not for the four days it will spend in your fridge.