How do you ripen lemons quickly off the tree?

I don't know about quickly, but you turn a pineApple on its top and leave it on the counter for a day or two. It should smell sweet when ripe. If you leave it in a brown paper bag, I think that makes it ripen faster. It's also really easy to tell when it is ripe. Pull gently on the leaves towards the top or center and if the feel loose or come out it is ripe. Hope this helps some. Pulling on the leaves of a pineApple will not tell you if a pineApple is ripe, its just a urban myth.