Ripe bananas release a lot of ethylene, the hormone that triggers ripening in mature fruit, so placing one in a closed paper bag with your under-ripe avocados will speed up the process. I tried it with a couple avocados that were just beginning to soften, and within 24 hours, they were perfectly soft and ready to eat.
Apples are another fruit that release a good amount of ethylene, so this would also work with a ripe apple.
Check it out: How to Deal with Unripened Avocados at Tasting Table
Do you have any tips for ripening an avocado more quickly?
(Image: Emma Christensen)