Freezing brown sugar can actually preserve its quality. When storing brown sugar, try to keep it in a cool area, which makes the freezer an ideal location.
As well as using the freezer, brown sugar can also be stored in a tight-lidded container. In that case, make sure that the container has no rust as this could negatively influence flavor. Never place brown sugar in the refrigerator.
When ready to use the frozen brown sugar, remove it from the freezer and let it return to room temperature for at least 2 hours. If the brown sugar has ice crystals, simply stir to remove these ice crystals and preserve quality.