Avocados don't ripen until after they're picked, so they often show up at the grocery store green and hard. It can take an avocado a week or longer to fully ripen at room temperature, and refrigerated storage just lengthens that amount of time. With a little planning, you can speed up the process so your avocados soften and develop their full flavor and creamy texture in less than week.
Place one to three avocados in a brown paper bag. The bag traps ethylene gas, which helps speed avocado ripening.
Place a ripe banana or apple in the bag with the avocados. The ripe fruit emits more ethylene gas to further speed the ripening of the avocado.
Fold the paper bag opening down to seal it closed and trap the gas. Leave the bag on the counter at room temperature for two to five days.
Check the avocados daily for ripeness. A ripe avocado yields slightly under gentle pressure and the skin usually changes from green to nearly black.