You can, but raw mushrooms come out of the freezer spongy and waterlogged, so cook them first. A mushroom is mostly water held in a soft structure, and ice crystals wreck that structure. Sauteing or steaming drives off the water before freezing, and the thawed result is close to fresh.
Why raw mushrooms turn spongy
Mushroom flesh has no rigid cell wall to speak of, unlike a carrot or a green bean. It is a loose network holding a very large volume of water. Freeze that water and it expands into crystals that push the network apart from the inside. There is nothing sturdy left to hold the shape once the ice melts.
Heat solves the problem by removing the water before it can freeze. A mushroom that has been cooked down has already collapsed on your terms, in a pan, with the flavor concentrating instead of running away. Freezing a cooked mushroom only has to preserve what is left, and what is left is mostly flavor and fiber.
This is also why washing matters. A mushroom held under a tap takes on water it did not have, and every extra gram becomes more ice. Brush or wipe them, and if something is genuinely dirty, rinse it quickly and dry it immediately.
The dry saute method, and why it beats butter
- Slice or quarter the mushrooms. Uniform pieces cook down at the same rate.
- Heat a wide pan over medium high with no fat at all and add the mushrooms in a single layer.
- Wait. They will squeak, then release a pool of liquid. Do not stir much during this stage.
- Keep the heat up until that pool boils away completely and the pieces start to squeak again and brown.
- Spread them on a tray to cool fully, then bag them flat, press out the air and label them.
Skipping the butter is deliberate. Fat carries odors through a freezer far more readily than water does, and cooking them dry means you get to choose the fat later. It also keeps the pieces loose rather than frozen into a greasy clump.
If a lot of liquid comes out, pour it into an ice cube tray and freeze it separately. That is concentrated mushroom stock and it belongs in gravy.
Steam blanching times by cut
Steaming is the alternative if you want the mushrooms pale rather than browned, for creamy dishes or soups. Soak them first for five minutes in water with a teaspoon of lemon juice stirred in per pint, which keeps them from darkening, then steam over boiling water for the times below and cool them in ice water immediately.
| Cut | Steam time |
|---|---|
| Whole button mushrooms | 5 minutes |
| Halved | 4 minutes |
| Quartered | 3 and a half minutes |
| Sliced | 3 minutes |
Storage window and cooking from frozen
Sauteed mushrooms taste best within about nine months, and steam blanched ones hold closer to twelve. Neither figure is a use by date. Freezing suspends bacterial growth for as long as the food stays frozen, and only flavor and texture decline over time.
Cook them from frozen. Tip a handful into a hot pan with butter and they behave almost like fresh ones, steaming for a moment and then catching color. They fold into risotto, pasta sauce, pie filling, omelets, gravy and stroganoff without any thawing step at all. The only time thawing helps is when they are headed into a blended soup, where texture is irrelevant anyway.
