Place the unwashed, unripe nectarines in a brown paper bag.
Roll the top of the bag loosely to close it. Ensure the bag doesn't get wet on the counter. As the fruit ripens, it releases ethylene in the bag, which hastens the process.
Place the paper bag on a counter or table -- somewhere it will remain at room temperature for one to two days.
Check the fruit every day until it is soft and yields to gentle palm pressure.
Store softened, ripe fruit in the refrigerator for a few days if necessary.