In short: Mushrooms are mostly water, and raw ones turn mushy when ice crystals form during freezing. Cooked or sautéed mushrooms stay firm and last 8 to 12 months at 0°F or below. Steaming is the top choice, but sautéing works too.
Why Cook Mushrooms Before Freezing?
Mushrooms contain a large amount of water. When you freeze a raw mushroom, something surprising happens: that water turns into ice crystals. As the crystals grow, they punch tiny holes in the mushroom's cell walls, pushing water out into the spaces around them. When you thaw the mushroom later, it collapses into a soggy, rubbery mess.
Cooked mushrooms are different. Heat breaks down the cell walls gently, so there is less water trapped inside to freeze. Ice crystals cannot damage what is already soft. This is why cooked mushrooms stay firm and tasty in the freezer for 8 to 12 months — but raw ones will not.
The Top Choice: Steam Your Mushrooms
Steaming is the top choice because it keeps mushrooms especially firm and fresh.
Here is how a grown-up does it:
- Wash the mushrooms gently and trim the stem ends.
- Dip them in a lemon juice solution (1 teaspoon lemon juice per pint of water) — this stops them from turning dark.
- Steam them: whole mushrooms for 5 minutes; button mushrooms or quartered pieces for 3½ minutes; thin slices for 3 minutes.
- Cool them quickly in ice water, then drain well on paper towels.
- Pack into freezer containers, leaving ½ inch of space at the top, seal, and freeze.
Steamed mushrooms will keep for 8 to 12 months at 0°F (–18°C) or colder.
An Easier Option: Sauté in Butter
If steaming feels like too many steps, try this simpler method:
- Wash and trim your mushrooms.
- Heat a little butter or oil in a frying pan over medium heat.
- Cook small amounts of mushrooms until they are almost done — they should look soft but not shrivelled.
- Cool them in the pan or put the pan in cold water to speed things up.
- Pack into containers, leaving ½ inch headspace, seal, and freeze.
This method is quicker and tastes delicious, though sautéed mushrooms will not stay quite as firm as steamed ones over long storage.
Storage and Thawing
Store frozen mushrooms at 0°F or below. The colder your freezer, the longer they last — aim for –18°C (0°F) or even lower if your freezer goes there.
When you are ready to use them, add them straight to a soup, stew, sauce, or pasta while still frozen. They will thaw as the dish cooks and give up all their flavour. Or thaw them overnight in the fridge and use them the same way you would fresh mushrooms.
Safety first: Never pick or eat wild mushrooms without an expert adult — look-alikes are impossible for non-experts to tell apart, and some wild mushrooms are very poisonous. The safe path is a grow kit or shop-bought mushrooms from a trusted store, always handled and cooked by a grown-up.
The Short Version
Cook or sauté mushrooms first, then freeze them. Raw mushrooms turn mushy because their water forms ice crystals; cooked ones stay firm and keep for 8 to 12 months at 0°F or below. Steaming is the top choice, but sautéing works too. Always let a grown-up handle the heat.
Curious questions
Why do raw mushrooms get mushy when frozen?
Mushrooms contain a lot of water. When water freezes, it forms ice crystals that poke holes in the mushroom's cells and push water out. When thawed, the mushroom collapses. Cooking first prevents this.
How long can you keep frozen mushrooms?
Cooked or sautéed mushrooms will stay good for 8 to 12 months when stored at 0°F (–18°C) or colder. Raw mushrooms should not be frozen at all.
Is steaming or sautéing better for freezing mushrooms?
Steaming is the top choice because it keeps mushrooms especially firm. But sautéing in butter is easier and still works well — the mushrooms will just be a tiny bit softer after thawing.
Can you cook frozen mushrooms straight from the freezer?
Yes! Add them straight to soups, stews, sauces, or pasta while frozen. They will thaw as the dish cooks and release their flavour. You can also thaw them overnight in the fridge first.
Why is it safer to buy shop mushrooms than pick wild ones?
Wild mushrooms have dangerous look-alikes that are poisonous. It is almost impossible to tell them apart. Shop mushrooms and grow kits are safe and do not need expert knowledge.
Sources & further reading
- National Center for Home Food Preservation — Freezing Mushrooms
- PMC/NIH — Ice Crystal Formation in Frozen Mushrooms
A note for growers: only grow and eat mushrooms from our kits or from species you know are safe, and always check with an adult. Never eat a wild mushroom unless an expert adult says it’s safe.
