Clean the mushrooms first: See the above tips for cleaning dry mushrooms or cleaning them quickly with tepid water.

Slice or chop (optional): If desired, you can slice or chop the mushrooms before freezing, but you can also freeze them whole. Slicing or chopping can be convenient for later use, as you can portion them according to your needs.

Pre-freeze: To prevent the mushrooms from clumping together, line a baking sheet with parchment and add mushrooms in a single layer. 

Place the baking sheet in the freezer for 1-2 hours or until the mushrooms are frozen.

Transfer the whole, sliced, or chopped mushrooms into airtight containers or heavy-duty freezer bags, removing as much air as possible. 

Label the bags with the date and type of mushrooms, then place them in the freezer for up to 12 months.