Ripe plantains are best for frying; they are black with bits of yellow, and they should be firm to the touch and not mush. Ripe plantains can be hard to find in major grocery stores, but you can easily ripen them at home. If you have the time, leave them to sit at room temperature for one to two weeks, or speed up the process by placing them in a brown paper bag; they will ripen in about 4-5 days using this method. Green or yellow plantains can be cooked, and they make amazing plantain chips.