If you have peaches that are not quite ripe yet place them in a brown paper bag and leave them at room temperature for a few days. The methane release from the peaches will be captured by the bag and help them ripen.
Most fruit will ripen pretty quickly by putting it in a brown paper bag for 1 -2 days. Fruit gives off ethylene, which is the substance they need for ripening. A brown paper bag will allow ripening without ripening.
