Tip 1: Place unripe avocados in a brown paper bag to ripen. This traps the ethylene gas they produce and helps them to ripen. A firm avocado placed in a paper bag will ripen at room temperature in about three to six days. As the fruit ripens, the skin color will darken.
Tip 2: Place avocados in a brown paper bag with a banana, (an apple or tomato works too), then leave the bag on a sunny windowsill for 18 to 24 hours.
Tip 3: Place 2 peeled, pitted avocados in a blender with 1 cup peas (fresh, or frozen and thawed); pulse until smooth. The peas will help soften the consistency of the unripe avocados but won’t affect the flavor.
Chart by CaliforniaAvocado.com blog site on the Five Stages that an avocado goes through as it is ripening.