Burying your fruit in uncooked rice is a quick and easy way to shave a few days off the ripening time. Just take something annoyingly slow to ripen, like a mango, and drop it into a bin of rice (the same rice already sitting in the kitchen is fine). Don't worry about ruining the rice, it'll be fine unless you forget the fruit's in the bin.
A container of rice makes it easy for the fruit's ethylene gas to stick around longer, and promote ripening. This works in much the same way that brown paper bags or or newspaper wrappings do. Using a method like this can reduce ripening time by entire days, but it's also a good way to overdo it. Just be sure to check on the fruit once or twice a day!
Mango in the Rice Bin: What's Going on Here? [The Kitchn]