If you find yourself with an unripe avocado, the best way to ripen the avocado is to place it in a brown paper bag at room temperature. The avocado will ripen in three to six days. In order to speed up the ripening process place an apple or banana in the brown paper bag to produce more ethylene gas. The avocado will ripen in one to three days.|If you have cut the avocado in half then realize that the avocado is not quite ripe, sprinkle the avocado with lime or lemon juice and put the two halves back together. Wrap the avocado in plastic wrap or place in an air tight container until the skin has darkened and the avocado is ripe.