Known as powdered sugar, icing sugar or confectioners sugar, it should be stored properly to prevent it from filling with bugs, lumping or absorbing strong odors and tastes. Powdered sugar combines finely ground cane sugar with cornstarch to prevent lumping from moisture in the air, but you will still need to keep it away from humidity. Like granulated sugar, powdered sugar has no expiration date, but if you store it incorrectly, you will not be able to reverse the damage. Rather than using a single storage system, use more than one to ensure you protect your powdered sugar against odors and moisture.
Things You'll Need
Transfer the powdered sugar from its original packaging into a zip top freezer bag and seal, pushing out excess air.
Place the sealed bag of powdered sugar into an air tight container.
Set the container into a cool, dry portion of the pantry, not the refrigerator, which has too much humidity.
Keep your powdered sugar in the pantry indefinitely as long as it does not pick up odors or develops lumps. Discard if this occurs.
Opt for freezer zip top bags which have a thicker construction to keep freezer odors at bay.
References and ResourcesCHSugar.com: FAQs