Although they're related to bananas, plantains are quite different -- larger, firmer, with a mild savory taste, although the ripest ones are slightly sweet. Unlike bananas, plantains must be cooked before eating, because they are too bitter and starchy when raw. When plantains turn dark brown or completely black, they're fully ripe and you need to cook them within a few days or store them properly to prolong their freshness.
Store the plantains at room temperature, uncovered and out of direct sunlight. Partially brown plantains continue to ripen when left out at room temperature. Keep them at room temperature until they have turned completely brown or fully black.
Store plantains that are completely brown or black in the refrigerator. They are fully ripened, but should be consumed within three to five days.
Freeze the brown or black plantains whole. Wrap them individually in plastic wrap and place them in the freezer. Use the frozen plantains within two to three weeks for the best flavor. However, you can keep them in the freezer for up to year.
Freeze peeled and mashed plantains. Peel the plantains and mash the flesh in a freezer-safe plastic container. Stir in a spoonful of lemon juice to prevent the plantain flesh from browning, and then cover and place in the freezer. Use the plantains as soon as possible, although you can keep them for up to a year.