Preservation by Freezing
Freezing can work as a good method for preserving mushrooms, but it's important to understand how it can affect their quality and determine the best method for your intended use.
Proper preparation before freezing mushrooms can help maintain their freshness, texture, and nutrients.
Over time, all frozen produce tends to lose some of its nutritional value. Mushrooms are a good source of nutrients like B vitamins, copper, potassium, and vitamin D (1, 2, 3).
While freezing doesn’t affect the calorie, fiber, or mineral content of foods, it can reduce the content of water-soluble vitamins like riboflavin, niacin, and folate. Keep in mind that fresh produce also loses nutrients over time. So you might choose a method based on what you most want to preserve.
Since raw mushrooms have an exceptionally high water content, they will become mushy if frozen raw and should always be cooked before freezing. Washing mushrooms can also make them soggy and lead to freezer burn. If you wish to clean them, simply brush or wipe them off.
Frozen mushrooms will last in the freezer for 10 to 12 months. These can be added directly to recipes that will be heated completely though, such as a soup or casserole. For others, best to thaw them in the fridge overnight before using.
Roasting and Blending
Our go-to method for preserving the harvest is to lightly toss our mushrooms with olive oil, garlic, and onions and roast on pans in the oven at 400F for 20 - 30 minutes, stirring a few times until lightly browned. We then blend this mixture in a food processor and pack into small plastic containers. This “base” can be used for many fillings, soups, spreads etc and is especially great to avoid any cosmetic blemishes or variability from “B” grade mushrooms.
Steam Blanching
Steam blanching is a quick cooking process that works by destroying enzymes that can increase how quickly foods spoil (4). An added benefit of steam blanching is that it inactivates Listeria and Salmonella, two common foodborne bacteria, improving the safety of the mushrooms prior to freezing them (5). Furthermore, blanching produce may help preserve nutrients (6, 7).
Blanching times vary depending on the size of the mushroom, so it’s a good idea to either sort them by size or cut them into similar-sized chunks before steaming. To prevent discoloration during the blanching process, first soak mushrooms in 2 cups (480 mL) of water and 1 teaspoon (5 mL) of lemon juice for 5 to 10 minutes.
To steam blanch your mushrooms, bring a pot of water to a boil and place a steamer basket inside. Add the mushrooms to the basket and let them steam for 3–5 minutes.
Then, remove the mushrooms and place them immediately into a bath of ice water for the same amount of time that you steamed them. Pat the mushrooms dry with a clean towel.
Once thoroughly cooled, place them in an airtight, freezer-safe bag and store them in the freezer.
Dry Sautéing
Sautéing is a method of dry heat cooking that uses a small amount of fat and relatively high temperature to soften and brown food quickly. Cooking this way without water may prevent the loss of B vitamins. Additionally, cooking with fat may improve the absorption of antioxidants and other plant compounds (8, 9, 10, 11).
Quick Steps
In a large skillet over medium-high heat, warm 1 tablespoon of oil. Add the mushrooms in a single layer and sauté until brown, about 3 minutes. Work in batches, adding more oil if needed. It's key to not add too much oil as the mushrooms will “drop” their water and you want to keep the pan as dry as possible, without being bone dry.
Cook them for approximately 5 minutes, until almost fully cooked. The mushrooms should become tender but not squishy.
Remove your mushrooms from the skillet and place them on a paper towel or plate to cool. Once thoroughly cooled, place them in an airtight, freezer-safe bag and store them in the freezer.
For more information on dry sautéing, check out our Basic Storage and Cooking page.
Flash Freeze for Best Taste
The best way to preserve mushroom flavor and texture is to flash freeze them after preparing using one of the methods above. While technically this is a process where items are exposed to cryogenic temperatures, or through direct contact with liquid nitrogen at −196 °C (−320.8 °F), we can mimic this process at home and still receive some of the benefits.
Ensure mushrooms are fully cool and patted dry, then spread the mushrooms on a rimmed baking sheet in a single layer. Place in the freezer for about 2 hours, or until the mushrooms are completely frozen. Use a spatula to transfer the frozen mushrooms into freezer bags or containers, leaving a half-inch of headspace for expansion, and return them to the freezer.
Squeeze out as much air as possible before you seal the containers. It will help to prevent freezer burn. Or vacuum pack if possible.
References
https://www.healthline.com/nutrition/can-you-freeze-mushrooms
https://www.thespruceeats.com/how-to-freeze-mushrooms-1388441