When crimini mushrooms mature and their tops extend, they take on the name portobello mushrooms. Around 6 inches in diameter, these large mature mushrooms boast an earthy flavor that gives them a whole new usefulness in cooking. In particular, they are ideal for sandwiches, especially since they can be grilled as vegetarian 'burgers' with ample room for toppings. If you don’t plan on using your bounty of portobello mushrooms in one single meal, the rest can be saved for the next time they’re needed.
Place fresh portobello mushrooms in paper bags or wrap them in paper towels for storage in the refrigerator. Plastic wrapping can trap in moisture and should be avoided. Portobello mushrooms kept in the refrigerator should be used within a week.
Wash portobello mushrooms that you intend to freeze under lukewarm running water to remove dirt and other debris.
Sauté the mushrooms in small batches with butter for five to six minutes each. The mushrooms can be sliced or left whole. For healthier mushrooms, sauté them in a non-stick pan without butter or steam-blanch them. Consider dipping the mushrooms into a solution of 1 tsp. lemon juice per pint of water before steam-blanching them. Set a steamer basket in a pot of boiling water to thoroughly steam the mushrooms on your stove for six minutes if they are whole and four minutes if they are in slices.
Transfer the cooked mushrooms into a container and set it into an ice bath to rapidly reduce their temperatures. Leave them to cool for at least 10 minutes.
Place the mushrooms into an airtight plastic container and mark it with the current date. If you don’t want to mark on the container itself, stick a piece of tape on it and write the date on the tape.
Place the mushrooms into the freezer right side up.