Hardened granulated white sugar can be softened by placing it into an oven, blending it or grating it, if it is a small amount. Sugar hardens when it is exposed to high humidity and moisture.
To soften white sugar in an oven, preheat an oven to 150 to 200 degrees Fahrenheit and place the hardened sugar into an ovenproof container. Bake the sugar for 15 minutes and tap with a spoon; if the sugar falls apart, turn the oven off and allow the sugar to dry for 1 to 2 hours before storing in an airtight container.
Sugar can also be softened by breaking it into smaller, more manageable pieces and placing it into a food processor, blender or grating it.